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1
Canevari, Thiago da Cruz 1980. "Ftalocianina de cobalto preparada in situ sobre o oxido misto SiO2/SnO2 obtido pelo processo sol-gel. Aplicação na oxidação eletrocatalitica do acido oxalico e do nitrito." [s.n.], 2008. http://repositorio.unicamp.br/jspui/handle/REPOSIP/249670.
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Orientador: Yoshitaka GushikemDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica
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Resumo: Este trabalho descreve a síntese do óxido misto SiO2/SnO2 nas composições 3%, 8,6% e 12% (% em massa de SnO2) obtido pelo processo sol-gel. As informações sobre a formação do SiO2/SnO2, foram obtidas utilizando as técnicas disponíveis para tal finalidade como área superficial pela técnica de BET, espectroscopia de fluorescência de raios X e difração em pó de raios X. O óxido misto SiO2/SnO2 foi utilizado como substrato para síntese in situ da ftalocianina de cobalto devido ser mecanicamente resistente, possuir alta área superficial e apresentar uma condutividade elétrica alta. A formação da ftalocianina de cobalto no material, SiO2/SnO2/CoPc, foi confirmada utilizando as técnicas de espectroscopia UV-VIS, espectroscopia IV e espectroscopia de fotoelétrons excitados por de raios X (XPS). Sendo assim, o material SiO2/SnO2/CoPc, foi utilizado na construção de eletrodos quimicamente modificados, no qual um eletrodo de pasta de carbono foi preparado para estudar a eletrooxidação do ácido oxálico e um eletrodo de disco rígido prensado foi preparado para estudar a eletrooxidação dos íons nitrito. Os estudos eletroquímicos foram realizados em solução aquosa de KCl 1 mol L utilizando as técnicas de voltametria cíclica, voltametria de pulso diferencial e cronoamperometria
Abstract: This work describes the synthesis on SiO2/SnO2 mixed oxide at compositions 3%, 8,6% and 12% (% in weight of SnO2) obtained sol-gel process. The information above the formation of SiO2/SnO2 were obtained use the available techniques for such objective like area superficial BET technique, ray X fluorescence spectroscopic and ray X diffraction. The SiO2/SnO2 mixed oxide was use like matrix for in situ synthesis cobalt phthalocyanine due be resistant mechanically, hold high superficial area and present high electric conductive. The formation of cobalt phthalocyanine on matrix, SiO2/SnO2/CoPc, was confirm used the techniques UV-Vis spectroscopic, IV spectroscopic and ray X spectroscopic photoelectron excited (XPS). Like this, the material SiO2/SnO2/CoPc was use for construction modified chemically electrodes, be the carbon paste electrode prepared for study the oxalic acid electooxidation and the rigid disc press electrode prepared for study the nitrite ions electooxidation. The electrochemical study were carry out in 1mol L KCl solution use the techniques cyclic voltammetric, differential pulse voltammetric and chronoamperometric
Mestrado
Quimica Inorganica
Mestre em Química
2
Jaussaud, Quentin. "Génération in situ d’isocyanates par décarboxylation d’acides oxamiques pour l’élaboration de matériaux polyuréthanes." Electronic Thesis or Diss., Bordeaux, 2024. http://www.theses.fr/2024BORD0139.
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Ces travaux de thèse portent sur la synthèse de polyuréthanes par génération in situ d’isocyanates, à travers différentes voies de moindre toxicité que la voie classique faisant appel à l’utilisation directe d’isocyanates. Dans un premier temps, la décarboxylation oxydante des acides oxamiques conduisant à la formation d’isocyanates a été réalisée par activation thermique grâce à l’utilisation d’un iodure hypervalent, jouant le rôle d’oxydant. Une étude cinétique sur des réactions modèles en présence d’alcool, associé à une modélisation numérique, ont notamment mis en évidence un effet catalytique de l’acide acétique, sous-produit de la réaction, sur la formation de liaisons uréthane. La formation de CO2 généré par cette réaction menant à la formation d’isocyanates, a ensuite été exploitée, pour la synthèse de mousses polyuréthanes réticulées. Les effets de différents paramètres, tels la nature des monomères ou la température de réaction, sur la morphologie et les propriétés des mousses obtenues ont ensuite été étudiés. Cette réaction d’activation des acides oxamiques a ensuite été réalisée par irradiation lumineuse en présence d’un photocatalyseur, permettant d’élaborer des films polyuréthanes. La modification des composés du mélange réactionnel a permis de développer des formulations homogènes, notamment en changeant la nature de l’iodure hypervalent utilisé. Enfin, la synthèse d’uréthanes et de polyuréthanes à partir de 1,4,2-dioxazol-5-ones a été explorée. Après une optimisation des conditions catalytiques permettant la génération d’isocyanates par ouverture de ces hétérocycles, le CO2 aussi formé a été exploité pour la production de mousses polyuréthanesThis PhD work focus on the synthesis of polyurethanes through the in situ generation of isocyanates, using pathways with lower toxicity compared to the classical approach involving the direct use of isocyanates. The oxidative decarboxylation of oxamic acids leading to the formation of isocyanates was, first, carried out by thermal activation using a hypervalent iodine as an oxidant. A kinetic study on model reactions in the presence of alcohol, combined with computational modeling, notably revealed a catalytic effect of acetic acid, a by-product of the reaction, on the formation of urethane bonds. The CO2 generated by this reaction, leading to the formation of isocyanates, was then exploited for the synthesis of cross-linked polyurethane foams. The effects of various parameters, such as the nature of the monomers or the reaction temperature, on the morphology and properties of the obtained foams were thereafter studied. This activation reaction of oxamic acids was then carried out by light irradiation in the presence of a photocatalyst, allowing the production of polyurethane films. Modifying the components of the reaction mixture enabled the development of homogeneous formulations, particularly by changing the nature of the hypervalent iodine used. Finally, the synthesis of urethanes and polyurethanes from 1,4,2-dioxazol-5-ones was explored. After optimizing the catalytic conditions for generating isocyanates through the opening of these heterocycles, the generated CO2 was exploited for the production of polyurethane foams
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Lee, Sung Oh School of Chemical Engineering & Industrial Chemistry UNSW. "Dissolution of iron oxides by oxalic acid." Awarded by:University of New South Wales. School of Chemical Engineering & Industrial Chemistry, 2005. http://handle.unsw.edu.au/1959.4/23924.
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The iron content of industrial minerals can be reduced by physical and chemical processing. Chemical processing is very efficient to achieve a high degree of iron removal at minimum operating cost. Both inorganic acids and organic acids have been used for clay refining. However, due to environmental pollution and contamination of products with the SO42- and Cl-, inorganic acids should be avoided as much as possible. This research investigated the use of oxalic acid to dissolve iron oxides and the dissolution characteristics of natural iron oxides. The dissolution of iron oxides in oxalic acid was found to be very slow at temperatures ranging from 25??? to 60???, but increased rapidly at a temperature above 90oC with increasing oxalic acid concentration, whereas the pH caused the reaction rate to decrease at pH>2.5 and improved the rate from pH 1 to pH 2.5. The iron oxides such as goethite (??-FeOOH), lepidocrocite (??-FeOOH) and iron hydroxide (Fe(OH)3) can be dissolved faster at the presence of magnetite which exhibits an induction period at the initial stage and showed the bell-shaped curves for the dissolution. In titration tests, however, the increase of temperature causes an increase in solubility of the oxalate complexes, resulting in an increased stability of ionized species in solution. During the addition of NaOH, NaHC2O4???H2O was precipitated without forming Na2C2O4???H2O, but it was re-dissolved at pH>4.0. On the other hand with NH4OH, NH4HC2O4???H2O and (NH4) 2C2O4???H2O co-precipitated at pH 0.93, but also re-dissolved at over pH 2.03. The reaction temperature was found not to affect the removal of iron from the ferric oxalate complex solution using lime. Iron is removed as iron hydroxide and calcium oxalate is then precipitated during the iron removal step. The formation of Fe(OH)3 in the solution was affected by the dissociation of Ca(OH)2. The thermodynamics of sodium, ammonium and iron oxalate complexes were investigated and the standard free energy, ??Go was calculated using thermodynamic data and solubility products. The dissolution of pure hematite by oxalate was found to follow a shrinking core model of which the kinetic step of the reaction is the controlled mechanism.
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Bottrill, Stephen. "Comparative studies of oxalyl-CoA decarboxylase produced by soil and ruminal bacteria." Title page, contents and abstract only, 1999. http://web4.library.adelaide.edu.au/theses/09ANM/09anmb751.pdf.
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Bibliography: leaves 139-167 The aim of this project was to identify an enzyme responsible for the metabolism of oxalate which would be suitable for degrading oxalate in the rumen, and clone and characterise that gene.
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McMullan, E. A. "The electrochemical reduction of carbon dioxide, glyoxylic acid and oxalic acid." Thesis, University of Ulster, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.356452.
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Tokimatsu, Toshiaki. "Biochemical Roles of Oxalic Acid in Wood Decay Model Systems and Characteristics of a New Oxalic Acid Producing Enzyme Glyoxylate Dehydrogenase." Kyoto University, 1999. http://hdl.handle.net/2433/182430.
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Kyoto University (京都大学)0048
新制・課程博士
博士(農学)
甲第7591号
農博第1030号
新制||農||773(附属図書館)
学位論文||H11||N3226(農学部図書室)
UT51-99-D208
京都大学大学院農学研究科林産工学専攻
(主査)教授 島田 幹夫, 教授 桒原 正章, 教授 中坪 文明
学位規則第4条第1項該当
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Ketusky, Edward. "Remediation of spent oxalic acid nuclear decontamination solutions using ozone." Thesis, Lancaster University, 2018. http://eprints.lancs.ac.uk/123625/.
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The Savannah River Site (SRS) has forty-three remaining very large underground tanks containing significant quantities of nuclear waste generated primarily from cold-war radiochemical separations. All of the tanks eventually must be closed. As part of decommissioning/closing the nuclear waste tanks, even residual quantities of the waste must be removed. Although most sludge can be removed mechanically, chemically cleaning (i.e. decontamination) with oxalic acid is used to aid in the removal of residual quantities. Although oxalic acid works for cleaning the tanks, its downstream impacts are considered detrimental. To better understand and quantify the impacts, detailed models were developed to account for different potential processing strategies for handling the spent oxalic acid nuclear decontamination slurries. Although the results vary, the models show that regardless of the oxalate handling strategies: 1) significant washing to decrease sodium concentration/solids concentration in vitrification feed will be required, and 2) the creation of copious future additions of feed for salt processing will be unavoidable. Using a Theory of Inventive Problem Solving (TRIZ) approach, a modified form of the Chemical Oxidation Reduction Decontamination (CORD) ultraviolet (UV) light was identified as being used with an analogous but already resolved problem that could be adapted to SRS HLW tank cleaning. A novel preliminary process called Enhanced Chemical Cleaning (ECC) was envisioned. As part of maturing the technology, the literature review identified three possible oxalate decomposition mechanisms associated with ECC. They are: 1)A heterogeneous non-Advanced Oxidation Process (AOP) mechanism where the target organic adsorbs onto the surface of a solid, often particulate, metal oxide at a so-called active site, followed by ozone attack on the sorbed organic; 2)A homogeneous non-AOP mechanism that operates under low pH acidic conditions and which involves complexation of the catalysing metal ion with the oxalate followed by ozone attack on the complex; and, 3)A homogeneous AOP mechanism that operates at a high basic pH and which involves metal ions catalysing the formation of hydroxyl radicals from ozone, with the said hydroxyl radicals then driving the oxalate decomposition. Process testing was conducted using slurries made from simulants designed to be chemically similar to real High-Level Waste (HLW) sludge types. Testing using slurries made from real HLW sludge was also performed, but because of safety limitations associated with handling HLW, only a much smaller scale test apparatus could be used. With the much smaller scale test apparatus, the purpose of the real HLW based testing was confirmatory. Each of the simulant decomposition test slurry was created using an Fe-rich or an Al/Mn-rich sludge simulant using either 1 wt% or 2.5 wt% oxalic acid. The real HLW based slurries were formed using 2 wt% oxalic acid. As part of the main postulate of this effort, both the simulant decomposition test slurries and real HLW based slurries demonstrate that UV light increased the decomposition rate. Even without UV, by adding only ozone, the oxalate decomposition was completed on an industrially relevant timescale. Also using simulant based testing, the overall oxalate decomposition exhibited four distinct stages related to the metal catalysts: Stage One – At short ozonation times, ozone decomposes Fe oxalates and solubilise Fe from ozone action on the metal oxide constituents of the sludge. Stage Two – At intermediate ozonation times, as a result of the loss of the solution capacity to complex (and so solubilise) Fe, Mn, and Ni ions due to O3 driven oxalate decomposition, as well as the pH increase that accompanies that decomposition, Fe begins to precipitate. Oxalate decomposition is still primarily catalysed by Fe ions during this stage. Stage Three – At intermediate ozonation times, Fe precipitation is near complete, and oxalate decomposition is now driven by ozone and Mn catalysis – Mn playing a major role in determining the final time to process endpoint of 1.1 × 10-3 M oxalate in solution. Stage Four – At long ozonation times, the process endpoint with Mn precipitation now near completion with Ni being the dominant metal ion in solution. Constructed plots compare the pH and remaining oxalate concentration, both as a function of time, suggesting some relationship. Regression analysis of the negative log of the oxalate concentration shows the R2 values are all greater than 0.80, confirming correlation. Thus, pH can be used as a field measure for confirming when oxalate decomposition is complete. As a principal hypothesis of this effort, using simulant based testing, both the scavenging effects of “all-ready present” nitrite (a soluble component of the sludge simulants) and oxalate mineralisation-derived carbonate are advantageously used in lieu of introducing hydroxyl radical probe compounds to the process. Specifically, differing nitrite concentrations between slurries showing no impact on the decomposition rates, and the build-up of carbonate not inhibiting the decomposition process strongly suggest that the decomposition is not the result of radicals. Instead, the oxalate decomposition is likely the result of a direct reaction of ozone with metal complexed oxalate (i.e. mechanism 2 discussed above).
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Watanabe, Tomoki. "Mechanisms for oxalic acid decomposition and transport in wood-rotting fungi." Kyoto University, 2008. http://hdl.handle.net/2433/136618.
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Kyoto University (京都大学)0048
新制・課程博士
博士(農学)
甲第13891号
農博第1706号
新制||農||955(附属図書館)
学位論文||H20||N4358(農学部図書室)
UT51-2008-C807
京都大学大学院農学研究科応用生命科学専攻
(主査)教授 梅澤 俊明, 教授 矢﨑 一史, 教授 江﨑 信芳
学位規則第4条第1項該当
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Lowalekar, Viral Pradeep. "Oxalic Acid Based Chemical Systems for Electrochemical Mechanical Planarization of Copper." Diss., The University of Arizona, 2006. http://hdl.handle.net/10150/193886.
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In an ECMP process, a wafer is anodically baised during polishing. The electrical potential is the driving force to oxidize copper metal to ions. Copper ions then react with chemistry in the electrolyte to go in solution or form a passivation layer on the surface. The passivation layer is removed by a very low downforce (0.5-1 psi), causing copper to electrochemically dissolve in solution. Passive film formation during copper ECMP is key to the success of this process, since passivation reduces dissolution in the recessed areas, while elevations on the copper surface in direct contact with the ECMP pad are electrochemically planarized. If no passive film forms, then copper removal will be conformal from the elevated and recessed areas, and planarity will be lost. Chemical formulations for the electrochemical mechanical planarization (ECMP) of copper must contain constituents that are stable at anodic potentials. A key component of the formulation is a corrosion inhibitor, which is required to protect low lying areas while higher areas are selectively removed. Organic compounds, which adsorb on copper at low overpotentials and form a film by oxidation at higher overpotentials, may be particularly useful for ECMP. The main goal of the research reported in this dissertation is to understand and develop oxalic acid-based chemical systems suitable for ECMP of copper through electrochemical and surface investigations. Special attention was paid to the development of an inhibitor, which can function under applied potential conditions. Physical methods such as profilometry and four point probe were used to obtain copper removal rates. An organic compound, thiosalicylic acid (TSA), was identified and tested as a potential corrosion inhibitor for copper. TSA offers better protection than the conventionally used benzotriazole (BTA) by oxidizing at high anodic potentials to form a passive film on the copper surface. The passive film formed on the copper surface by addition of TSA was characterized by X-ray photoelectron spectroscopy. The oxidation potential of TSA was characterized using cyclic voltammetry. The passivation and repassivation kinetics was investigated in detail and a passivation mechanism of copper in oxalic acid in the presence of TSA is proposed. Copper removal experiments were performed on a specially designed electrochemical abrasion cell (EC-AC) in both the presence and absence of inhibitors. The effect of anodic potentials on the dissolution of copper was studied to identify suitable conditions for the electro-chemical mechanical planarization process.
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Beaulieu, Robert A. "Oxalic acid production by sclerotinia homoeocarpa the causal agent of dollar spot /." Connect to resource, 2008. http://hdl.handle.net/1811/32174.
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Missengue-Na-Moutoula, Roland. "Synthesis of ZSM-5 zeolite from South African fly ash and its application as solid catalyst." University of the Western cape, 2016. http://hdl.handle.net/11394/5431.
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Philosophiae Doctor - PhDZeolites are widely used as environmentally friendly solid catalysts or catalyst supports in the refining and petrochemical industries. ZSM-5 zeolite is composed of a three-dimensional medium pore structure (openings of 5-5.5 Å) with high silica content, high temperature stability and strong acidity making it a well-known and an established catalyst for several petroleum derived chemical processes such as cracking, aromatic alkylation, disproportionation, Methanol-to-Gasoline, isomerisation, etc. Nowadays, the synthesis of ZSM-5 zeolite from silica, alumina sources and structure directing agents (templates) is well known. Its synthesis is possible from fly ash, which is a low cost source of both silica and alumina. Fly ash is an inorganic residue resulting from the combustion of coal in electricity generating plants, consisting mostly of SiO₂ and Al₂O₃. ZSM-5 zeolite has not been synthesised from South African coal fly ash and the literature reports that fly ash-based ZSM-5 zeolite was synthesised only with tetrapropylammonium (TPA+) as structure directing agent and required an excessive amount of additional silica. The final ZSM-5 product was reported to still contain fly ash mineral phases after synthesis. This prevents the use of fly ash as a ZSM-5 zeolite precursor. Moreover, the synthesis of a high purity ZSM-5 zeolite from fly ash without additional silica has not been yet reported. This study aimed to synthesise high purity ZSM-5 zeolite from South African coal fly ash without additional silica, and with tetrapropylammonium bromide (TPABr), 1,6- hexanediamine (HDA) or 1-propylamine (PA) as structure directing agent. This aim was achieved by first optimising the synthesis of ZSM-5 zeolite from South African coal fly ash based on a formulation reported in the literature with fumed silica and TPABr as additional source of silica and structure directing agent respectively. Thereafter, the obtained optimum conditions were used to synthesise other fly ash-based ZSM-5 zeolite products by substituting TPABr with HDA or PA. Two routes of treating the as-received fly ash prior to the hydrothermal synthesis were applied in order to improve the quality of the final products or reduce the amount of the fumed silica that was used. The first route consisted of treating the as-received fly ash with concentrated H₂SO₄ in order to remove a certain amount of aluminium and increase the Si/Al in the acid treated fly ash solid residue but also remove some other elements such as Fe, Ca, Mg, and Ti which might have an undesirable effect on the product quality. The acid treated fly ash solid residue was used as ZSM-5 precursor with fumed silica as additional silica source and TPABr, HDA or PA as structure directing agent. The ZSM-5 zeolite products that were synthesised from the as-received fly ash as well as from the H₂SO₄ treated fly ash were treated with oxalic acid solution in order to reduce the aluminium content in the final products. The second route consisted of fusing the as-received fly ash with NaOH and treating the powder fused fly ash extract with oxalic acid solution. The obtained fused and oxalic acid treated fly ash extracts were used as ZSM-5 precursors without additional fumed silica and with TPABr, HDA or PA as structure directing agent. ZSM-5 zeolite was synthesised from the as-received South African coal fly ash not only with the commonly used structure directing agent TPABr but also with two other, lower cost structure directing agents, HDA and PA. The synthesis process did not generate any solid waste as fly ash was used as bulk, which could be a way of valorising South African coal fly ash. However, the final products contained some fly ash mineral phases such as mullite and quartz, and had poor physical and chemical properties compared to a commercial H-ZSM-5 zeolite. The treatment of the as-received fly ash with H₂SO4 resulted in fly ash-based ZSM-5 zeolite products with better physical and chemical properties than those of ZSM-5 zeolite products that were synthesised from the as-received fly ash. Moreover, the post-synthesis treatment of the fly ash-based ZSM-5 zeolite products with oxalic acid resulted in an increase in the Si/Al ratio, offering a post-synthesis route to adjust the acidity of the catalysts. However, mullite and quartz phases were still present in the synthesised products. Alternatively, high purity ZSM-5 zeolite was synthesised from the fused and oxalic treated fly ash extracts without additional silica and with TPABr, HDA or PA as structure directing agent. Moreover, these synthesised fly ash-based ZSM-5 zeolite products had similar physical and chemical properties to the commercial H-ZSM-5 zeolite. The synthesised fly ash-based ZSM-5 zeolite products were used as solid catalysts in the Methanol-to-Olefins (MTO) and Nazarov reactions. The ZSM-5 zeolite products that were synthesised from the H₂SO4 treated fly ash as well as fused and oxalic treated fly ash were successfully used as solid catalysts in the MTO and Nazarov reactions. The ZSM-5 zeolite products that were synthesised from the H₂SO₄ treated fly ash presented a similar trend in MTO and Nazarov reactions depending on the structure directing agent that was used, and the ZSM-5 zeolite that was synthesised with HDA as structure directing agent had the highest MTO and Nazarov conversion. However these catalysts deactivated more quickly compared to the commercial H-ZSM-5 zeolite. On the other hand, the zeolites that were synthesised from the fused and oxalic acid treated fly ash had a high initial MTO conversion equivalent to the commercial H-ZSM-5 zeolite. However, they deactivated after 5 h of time on stream due to diffusional constraints, because of their large crystal sizes. This study developed novel routes in the synthesis of high value zeolites from fly ash. ZSM-5 zeolite was synthesised from fly ash with structure directing agents other that TPA+ cation and had acceptable Brønsted acidity and high initial conversion in MTO and Nazarov reactions. This has not been yet reported in the literature. Moreover, for the first time a high purity ZSM-5 zeolite was synthesised from fly ash without additional silica and had similar properties to a commercial H-ZSM-5 zeolite. This constituted a breakthrough in the fly ash-based ZSM-5 zeolite synthesis procedure, which will promote the valorisation of fly ash through ZSM-5 synthesis due to avoiding the addition of silica source in the hydrothermal gel and preventing the presence of fly ash mineral phases in the final products. This study can have a significant economic and environmental impact in South Africa if the synthesis process is scaled up as it provides a potentially cheap and innovative way of using waste for making a high value green and acid catalyst, namely ZSM-5 zeolite that has several catalytic applications; and it promotes the valorisation of South African coal fly ash that is considered by many as waste material.
National Research Foundation (NRF)
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Tsai, Suh-Jen Jane. "Equilibrium and kinetic studies of metal ion promoted hydration and enolization reactions of oxaloacetate in various buffers : the cooperativity with base catalysts /." The Ohio State University, 1985. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487258254024045.
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Tranca, Ionut [Verfasser]. "Density functional study of molecular adsorption on the Cu(011) surface : oxalic acid and 2,5 pyrazine di-carboxylic acid / Ionut Tranca." Aachen : Hochschulbibliothek der Rheinisch-Westfälischen Technischen Hochschule Aachen, 2012. http://d-nb.info/1022616684/34.
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Ribeiro, Emerson Schwingel. "Estudos das atividades eletrocataliticas das ftalocianinas de Co (II) e Fe (II) tetrassulfonadas suportadas sobre silica gel quimicamente modificada com ion piridinio." [s.n.], 1999. http://repositorio.unicamp.br/jspui/handle/REPOSIP/249658.
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Orientador: Yoshitaka GushikemDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Quimica
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Mestrado
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Azzu, Youssef Mohamed. "Modulation of fruit ripening, storage time and quality of fruits with emulsion of Chitosan alone and loaded with Salicylic acid or Oxalic acid." Thesis, Curtin University, 2016. http://hdl.handle.net/20.500.11937/576.
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Efficacy of chitosan emulsion, salicylic acid (SA) or oxalic acid (OA) alone and chitosan loaded with SA or OA on ethylene production, extending storage life and maintenance of climacteric (nectarine and plum) and non-climacteric fruit (sweet orange) quality at ambient temperature and cold conditions was investigated. Beneficial effects of these coating treatments in regulating ethylene production, fruit softening, reducing weight loss and diseases and quality parameters varied between climacteric and non-climacteric fruits, cultivars and storage conditions.
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Kerman, Ipek. "Synthesis And Characterization Of Poly(oxalic Acid Dithiophen-3-yl Methyl Ester) And Thiophene Ended Poly-&." Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/2/12605014/index.pdf.
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Synthesis and characterization of thiophene ended poly-ε
-caprolactone (PCL) and oxalic acid dithiophen-3-yl methyl ester (ODME) and their copolymers with both pyrrole and thiophene were achieved. Chemical structure of the precursor polymer and monomer were investigated Redox behavior of polymer and monomers were determined by Cyclic Voltammetry (CV). Structural characterization of samples were carried out by 1H, 13C Nuclear Magnetic Resonance (NMR) and Fourier Transform Infrared Spectroscopy (FTIR). Conductivities of the films were measured by using four probe technique. Thermal analyses of conducting copolymers were investigated via Differential Scanning Calorimetry (DSC) and Thermal Gravimetry Analysis (TGA). The morphologies of the copolymer films were examined by Scanning Electron Microscopy (SEM). Electrochromic and spectroelectrochemical behavior of the copolymers were investigated, and their ability of employment in device construction has been examined.
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Eaton, Gregory K. "Oxalic acid production by the ectomycorrhizal fungus Hebeloma westraliensis and its role in the nutrient acquisition and growth of Eucalyptus diversicolor in calcareous soil." Thesis, Virginia Tech, 1994. http://hdl.handle.net/10919/41292.
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This work includes an introduction and literature review of mycorrhizal enhancement of the mineral nutrition of host plants. Particular attention was paid to the role of mycorrhizae in acquiring P from inorganic phosphates. Two experiments were designed to study a mechanism by which the ectomycorrhizal fungus Hebeloma westraliensis can enhance the availability and absorption of P from Ca phosphate by Eucalyptus diversicolor in calcareous soil. Chapter 2 reports on a study on the growth and oxalic acid production of H. westraliensis in calcareous and noncalcareous liquid media. Oxalic acid is thought to chelate cations from phosphate precipitates allowing the release of phosphate into solution. L-threonine was added as an additional treatment to asses the ability of this amino acid to inhibit oxalic acid production by the fungus. Growth and oxalic acid production of H. westraliensis were increased in the calcareous systems. L-threonine had little effect on dry weight of mycelium but substantially reduced oxalic acid production in the calcareous media. Chapter 3 reports on a study of E. diversicolor X H. westraliensis mycorrhizal synthesis in model calcareous and noncalcareous systems. Oxalic acid production was measured in these systems as well as various measurements of solution and host plant nutrition. Solution P concentration decreased and solution Ca increased in the calcareous systems. Mycorrhization decreased the solution concentrations of both of these nutrient elements, due partly to sequestration of these elements in fungal and plant tissues. Plant tissue P concentration was decreased and tissue Ca concentration increased in the calcareous systems. Mycorrhization increased the concentrations of both of these elements in plant tissues. Mycorrhization also increased the height and dry weight of seedlings at harvest and ameliorated symptoms of nutrient deficiencies seen in nonmycorrhizal plants in the calcareous system. Oxalic acid production by the fungus and by the plant were increased in the calcareous system. Attempts to correlate oxalic acid production with solution and plant nutrition were unsuccessful. The relationships of these results to the mycorrhizal enhancement of plant nutrition in calcareous soil is discussed.Master of Science
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Erman, Munir. "A Novel Mechanism for Oxalic Acid Biosynthesis Coordinating with Energy Generating Systems in the Wood-Rotting Basidiomycete Fomitopsis palustris." Kyoto University, 2002. http://hdl.handle.net/2433/149889.
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Kyoto University (京都大学)0048
新制・課程博士
博士(農学)
甲第9597号
農博第1225号
新制||農||840(附属図書館)
学位論文||H14||N3629(農学部図書室)
UT51-2002-G355
京都大学大学院農学研究科応用生命科学専攻
(主査)教授 島田 幹夫, 教授 加藤 暢夫, 教授 江﨑 信芳
学位規則第4条第1項該当
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Tyler, Simon Nicholas George. "Asymmetric synthesis using enantiopure dihydro-2H-1,4-oxazin-2-one templates." Thesis, University of Reading, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266800.
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Sjöde, Anders. "Chemical characterization in the biorefinery of lignocellulose : formation and management of oxalic acid and analysis of feedstocks for bioethanol production /." Karlstad : Faculty of Technology and Science, Chemistry, Karlstad University, 2008. http://www.diva-portal.org/kau/abstract.xsql?dbid=1362.
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Bajunaid, Mohammad. "Electrodeposition of Hydrogen Molybdenum Tungsten Bronze Films and Electrochemical Reduction of Carbon Dioxide." Digital Commons @ East Tennessee State University, 2021. https://dc.etsu.edu/etd/3857.
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The foremost aim for performing this study was to focus on the electrodeposition of mixed hydrogen molybdenum tungsten bronze films, which have the potential for e– transfer interactions carrying out the reduction of carbon dioxide. A yellow peroxymolybdic tungstate solution was prepared and used for the electrodeposition of hydrogen molybdenum tungsten bronze films on conductive carbon paper. Electrodeposition was carried out at -2.0 V from 20 - 120 minutes to determine the effect of deposition time on film thickness and CO2 reduction. These films were characterized by X-ray photoelectron spectroscopy. The deposited films served as a working electrode for CO2 electrochemical reduction utilizing 0.8 M NaHCO3 as the electrolyte. Carbon dioxide gas was bubbled into the cathode solution for an hour while bulk electrolysis was carried out at different applied potentials. Products were identified and evaluated using ion chromatography.
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Ndlovu, Bongani. "Kimberlite weathering : effects of organic reagents." Diss., University of Pretoria, 2013. http://hdl.handle.net/2263/33354.
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Diamonds are commonly present in an ore called kimberlite. Kimberlites vary extensively in mineralogy and therefore can complicate the processing and the extraction of diamonds. Weathering of kimberlite was investigated in this study and refers to the rapid physical breakdown of the kimberlite material. Kimberlite weathering by organic molecule adsorption was investigated utilising organic solutions; ethanol, formamide, n-hexane, oxalic acid, urea, pentanoic acid and acetic acid, was investigated. The extent of weathering was measured by XRD, TGA and FTIR analysis as well as by evaluating changes in the particle size distribution. The idea to predict the susceptibility of weathering of kimberlite based on TGA analysis was discredited as it was found that there was no correlation between the smectite content and the % weight loss from TGA analysis.
In XRD analysis studies to relate the d-spacing to the extent of weathering, it was found that the technique was not sensitive enough to enable direct prediction of weathering behaviour. Organic solutions at 0.5 M generally did not significantly alter the d-spacing. In the case of utilising pure organic solutions, it was observed that switching from diluted to pure organic solutions did not increase the d-spacings but rather lowers the space. Cation pretreatment prior to organic weathering resulted in d-spacings up to 2 water layers (12.6 Å being equal to 1 water layer, 15.6 Å equal to 2 layers and 18.6 Å equal to 3 layer). The general trend was that the divalent cations Mg2+ and Ca2+ increased the d-spacings whereas monovalent cations Na+ and K+ decreased the spacing. In the case of pre-organic treatment prior to organic weathering, it was observed that the resulting d-spacing increased to 2 and 3 water layers.
TGA analysis confirmed that the kimberlite structure did absorb organic reagents during weathering. It was observed that the amount of organic reagents adsorbed decrease in the following order: oxalic acid > urea > pentanoic acid > formamide > ethanol > n-hexane > acetic acid, with oxalic acid having been adsorbed the greatest. In addition, it was also shown that the extent of inorganic cation adsorption was more than that of organic solutions. The analysis also showed that organic pretreatments yielded promising results and the order followed was dimethyldioctadecylammonium chloride > cetylpyridium chloride > dodecylamine > pyridine in encouraging subsequent organic adsorption. FTIR analysis results indicated the mechanism by which organic molucules attached onto the mineral surface. It was observed that there was a disturbance of the bond between water in the interlayer and the silicate structure by a stronger H-bond gained through organic molecule attachment. Oxalic acid was observed to cause a structural change due to proton attack of the silicate structure.
It was found that kimberlite weathering, in essence, occurred in the first 24 hours of contact with the solution. Oxalic acid was found to be the most effective weathering agent compared to the rest of the tested organic solutions. The effect of the tested solutions, at 0.5 M concentration, on kimberlite weathering followed the series Cu2+ > oxalic acid > ethanol > acetic acid > formamide > n-hexane > distilled water. This study therefore showed that the accelerated weathering of kimberlite utilising organic solutions was not as efficient as the Cu2+ solution. Comparing Cu2+ and oxalic acid treatments, results showed that 67 % of the particles passed 12 mm screen size due to Cu2+ weathering as opposed to 48 % in oxalic acid.
In investigating the effects of variables, it was found that time of exposure had a small effect in the weathering of kimberlite. Increasing the organic concentration from 0.025 M to 0.5 M saw an increase in the amount of particles passing the 12 mm screen size by~20 %. There was however no improved weathering when the solution temperature was increased from approximately 25 °C to 40 °C.
In the study of kinetics involved during organic weathering utilising oxalic acid and comparing with Cu2+ medium, a high mineral dissolution was observed in the first 24 hours of contact with the weathering solution. However, different weathering mechanisms were observed between Cu2+ and oxalic acid. Inorganic solutions foster weathering by interlayer cation exchange which results in the reduction of the surface energy and this encourages further crack propagation. Oxalic acid weathering mechanism was by proton attack of the structural cations which was then limited thereafter by oxalate salts precipitation. Al3+ and Mg2+ were the dominant cations in solution during weathering (reaching 40 mmol/L) at higher oxalic acid concentration. This indicated that the dissolution of the clay‟s octahedral structure occurred, making oxalic acid a more effective agent than the rest of the tested organic solutions.
An alternative method to transform non-swelling clay minerals to swelling in kimberlites was highlighted. It was observed that cation exchange treatment in conjunction with acid and oxidation treatments on kimberlites containing non-swelling minerals: mica or forsterite that are at least 30 % in quantity may result in the presence of swelling clays after these treatments. Kimberlite that contained serpentine minerals was more resistant to alteration under these conditions.Dissertation (MEng)--University of Pretoria, 2013.
gm2014
Materials Science and Metallurgical Engineering
UPonly
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Baptista, José Antonio Avelar. "Avaliação do poder de inibição do ácido oxálico frente ao aço carbono em soluções de diferentes pH's." Florianópolis, SC, 1998. http://repositorio.ufsc.br/xmlui/handle/123456789/77884.
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Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências Físicas e Matemáticas. Programa de Pós-graduação em Química.Made available in DSpace on 2012-10-17T08:23:00Z (GMT). No. of bitstreams: 0
Estudou-se o comportamento do Ácido Oxálico como inibidor de corrosão para o aço-carbono em soluções de diferentes pH#s (2,5 6,0). Empregou-se como métodos de análise o método gravimétrico (perda de massa por unidade de área de tempo) e o eletroquímico, empregando-se as técnicas Ecorr vs. tempo e curvas de polarização potenciodinâmicas. Os dois métodos mostraram-se concordantes e indicaram que as taxas de corrosão do aço-carbono diminuem com o passar do tempo, independente do pH e da concentração do inibidor empregada. Os ensaios Ecorr vs. tempo indicaram que o Ácido Oxálico é um inibidor catódico, agindo sobre a reação de desprendimento de hidrogênio. Os estudos mostraram que o Ácido Oxálico atua como inibidor de corrosão eficiente quando o pH da solução é ³ 4,0 e quando a concentração de Ácido Oxálico é da ordem de 10-7 10-5 M. Nestas condições atinge-se uma eficiência de proteção da ordem de 50% de acordo com os ensaios gravimétricos e de 75% de acordo com os ensaios eletroquímicos. A atuação do inibidor foi interpretada levando-se em conta a distribuição das espécies de Ácido Oxálico em solução em função do pH, atribuindo-se a atividade inibidora preferencialmente devido à presença de oxalato.
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Bengraine, Karim. "Ozonation de solutions aqueuses : role de l'eau oxygenee." Paris 7, 1988. http://www.theses.fr/1988PA077176.
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Contribution a la meilleure connaissance des phenomenes impliques dans une filiere de traitement de l'eau, avec un interet plus particulier au role de l'eau oxygenee au cours de l'ozonation de solutions aqueuses. Etude de l'ozonation de molecules organiques (acides salicylique, phtalique et oxalique), des mecanismes mis en jeu et comparaison des produits obtenus par ozonation et par reaction de fenton
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Cherrad, Semcheddine. "Étude de la réponse adaptative du champignon filamenteux Botrytis cinerea à différents stress métalliques." Thesis, Lyon 1, 2011. http://www.theses.fr/2011LYO10182.
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De nombreux métaux sont indispensables au métabolisme cellulaire, d’autres sont considérés toxiques même à de faibles concentrations. Différents champignons appartenant à des différents groupes taxonomiques ont été identifiés dans des milieux pollués et ont révélé une capacité à survivre et à croître en présence de concentrations potentiellement toxiques. Pour s'adapter à ce stress, les champignons ont développé plusieurs mécanismes au niveau intracellulaire et extracellulaire. En particulier, ils sont connus pour leur capacité à sécréter un large panel de protéines. Cependant, leur rôle dans l'adaptation des champignons à la toxicité des métaux n'a pas encore été étudié. Pour répondre à cette question, le champignon Botrytis cinerea a été soumis à un stress métallique en présence de cuivre, zinc, nickel ou cadmium, les protéines sécrétées ont été collectées et séparées par 2D-PAGE. Deux métabolites ont également été analysés, l'acide oxalique et la nicotianamine. Enfin, les capacités de biosorption des champignons isolés à partir de sols pollués ont été étudiées. L'analyse du sécrétome a révélé 116 spots dont le volume varie en réponse d'au moins un métal. Cinquante-cinq de ces spots sont associés à des protéines uniques. La classification fonctionnelle de ces protéines a révélé que la production d'oxydoréductases et des enzymes dégradant la paroi cellulaire a été modifié en réponse aux métaux. L’étude de la production d'acide oxalique par Botrytis cinerea en réponse aux métaux montre une induction de la sécrétion d'oxalate en réponse au Zn et une accumulation de la nicotianamine, métabolite intracellulaire capable de fixer les métaux chez les plantes. Le gène de la nicotianamine synthase, est d’ailleurs surexprimé en présence de Cu, Zn et Ni. Plusieurs espèces fongiques ont été isolées à partir de sols pollués par des métaux, parmi ceux-ci Trichoderma asperellum et Zygorrhynchus moelleri montrent les meilleurs capacités de biosorption (10mg de Cu/g de matière sèche) des ions CuMetal ions are essential elements in many cellular processes. However, metal excess becomes toxic and constitutes a global environmental hazard. A range of fungi from all major taxonomic groups were found in metal-polluted habitats and the ability to survive and grow in the presence of potentially toxic concentrations is frequently encountered. To adapt to this stress, fungi have evolved several mechanisms at both intracellular and extracellular levels. In particular, fungi are well known for their ability to secrete a large panel of proteins. However, their role in the adaptation of fungi to metal toxicity has not yet been investigated. To address this question, here, the fungus Botrytis cinerea was challenged to copper, zinc, nickel or cadmium stress and secreted proteins were collected and separated by 2D-PAGE. Two metabolites were also analyzed, oxalic acid and nicotianamine. Finally, biosorption capacities of fungi isolated from polluted soils were investigated. Secretome analysis revealed one hundred and sixteen spots whose volume varied in at least one tested condition were observed on 2D gels. Fifty-five of these spots were associated with unique proteins and functional classification revealed that the production of oxidoreductases and cell-wall degrading enzymes was modified in response to metals. Study of oxalic acid and nicotianamine (NA) production by Botrytis cinerea in response to tested metals reveal that Zn induces oxalate secretion and that NA synthase gene is upregulated in presence of Cu, Zn and Ni. Many fungal species were isolated from metal polluted soils among them Trichoderma asperellum and Zygorrhynchus moelleri which show the maximum biosorption capacities of Cu ions
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Ibrahim, Mohamed Asim Y. "Co-processing of drugs and co-crystal formers and its effect on pharmaceutical dosage-form performance. Co-crystallization of urea/ 2-methoxybenzamide, caffeine/ malonic acid, caffeine/ oxalic acid and theophylline/ malonic acid systems: Solid-state characterization including imaging, thermal, X-ray and Raman spectroscopic techniques with subsequent evaluation of tableting behaviour." Thesis, University of Bradford, 2008. http://hdl.handle.net/10454/12760.
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This dissertation has focused on the solid-state characterization of different co-crystal system as well as the effect of co-crystallization of these systems on pharmaceutical dosage form performance. Urea/ 2-MB, caffeine/ malonic acid, caffeine/ oxalic acid and theophylline/ malonic acid co-crystals were prepared using co-grinding- and co-precipitation techniques. In addition, the synthesis of co-crystals through two novel methods has been demonstrated. This includes compaction and convection mixing. The solid-state characterization of the co-crystals has been carried out using XRPD, Raman spectroscopy, DSC, TGA, hot-stage microscopy and SEM. After preparation of co-crystals, tablets have been produced from co-ground-, co-precipitated-, and physical mixtures using Compaction Studies Press (Kaleva), and the data were recorded to compare between the different mixtures, regarding compactibilty, compressibility and deformational properties. The DSC results showed that the physical mixtures of all systems, formed co-crystals during heating process. For systems of urea/ 2-MB, caffeine/ malonic acid and theophylline/ malonic acid, the co-ground mixture produced tablets with higher tensile strength compared with either co-precipitated or physical mixture. However, for caffeine/ oxalic acid system, the tensile strengths of compacts produced from the physical mixture were greater than those obtained from either co-ground or co-precipitated mixtures. The Heckel data suggested that urea/ 2-MB, caffeine/ malonic acid and theophylline/ malonic acid systems are Type 1 materials, as an extensive linearity during compression was indicative of a plastic deformation mechanism, while the caffeine/ oxalic acid system was Type 2 materials. However, the co-precipitated mixture of urea/ 2-MB system was the least compressible, as it possessed the greatest value of yield pressure (85 MPa) and the highest elastic recovery (7.42%). The co-precipitated mixture of both of caffeine/ malonic acid and theophylline/ malonic acid systems was the most compressible with small yield pressure values of (44 & 80 MPa) and elastic recovery of (7.2% & 6.56%), respectively. The co-ground mixture of caffeine/ oxalic acid possessed the highest value of yield pressure (166 MPa) and thus the lowest compressibility among other mixtures. Furthermore, the addition of microcrystalline cellulose and α-lactose monohydrate has affected the crystallinity as well as the tableting properties of the co-crystals. After the addition of excipients, the tensile strength of compacts was about 2 times higher than any other mixture. Finally, urea/ 2-MB and caffeine/ malonic acid co-crystals were successfully synthesized through convection mixing and compaction.Islamic University of Omdurman and the Ministry of Higher Education in Sudan
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Lima, Darlon Martins [UNESP]. "Avaliação da resistência de união de diferentes sistemas adesivos à dentina bovina: influência de agentes dessensibilizantes." Universidade Estadual Paulista (UNESP), 2005. http://hdl.handle.net/11449/89648.
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lima_dm_me_arafo.pdf: 826526 bytes, checksum: ff1d690d6b0676f46d0b484cb8adef94 (MD5)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)
O objetivo deste trabalho foi o de avaliar comparativamente in vitro, a resistência de união ao cisalhamento de uma resina composta à dentina bovina em função da combinação de três diferentes sistemas adesivos e de dois diferentes agentes dessensibilizantes. Foram utilizados os sistemas adesivos: Single Bond, Master Bond e Prime & Bond 2.1 e os seguintes agentes dessensibilizantes: o Oxagel e o G. H. F. Dessensibilizador. Para a confecção dos corpos de prova, 90 incisivos bovinos (n=10) foram utilizados, os quais tiveram suas superfícies vestibulares desgastadas, até a exposição dentinária, de tal forma que, a área de adesão padronizada, tivesse 4 mm de diâmetro. Após a realização dos tratamentos de superfície, onde os Grupos controle eram indicados apenas pela aplicação do sistema adesivo, e os Grupos experimentais, pela aplicação dos agentes dessensibilizantes testados após o condicionamento ácido, foram confeccionados cilindros de resina composta Z-100, com o auxílio de uma matriz bipartida. Os corpos-de-prova foram então armazenados em água destilada a 37°C por 24 horas, e submetidos em seguida ao ensaio de cisalhamento, a uma velocidade do atuador de 0,5 mm/min. Os resultados obtidos foram submetidos à análise de variância, e ao teste de Tukey, ao nível de 5% de significância. Observou-se que houve influência dos agentes dessensibilizantes, quando estes eram aplicados na dentina bovina e interagiam com os sistemas adesivos, sendo que o G. H. F. Dessensibilizador aumentou estatisticamente os valores de resistência de união do Single Bond, e do Prime & Bond 2.1, e o Oxagel não influenciou nos valores de resistência de união dos sistemas adesivos testados.
The objective of this work was it of evaluating in vitro comparatively , the shear bond strength of a resin composed to the bovine dentin in function of the combination of three different adhesive systems and of two different agents dessensitizers. The adhesive systems were used, to know: Single Bond, Master Bond and Prime & Bond 2.1 and the following agents dessensitizers: Oxagel and G. H. F. Desensitizer. For the making of the test bodies, 90 incisive bovine (n=10) they were used, which had its worn away vestibular surfaces, until the exhibition dentin, in such a way that, the area of standardized adhesion, had 4 diameter mm. After the accomplishment of the surface treatments, where the Groups control was just suitable for the application of the adhesive system, and the experimental Groups, for the application of the agents dessensitizers tested after the acid conditioning, cylinders of composed resin were made Z-100, with the aid of a bipartite matrix. The test bodies, they were stored then in water distilled for 37°C by 24 hours, and submitted soon after to the shear bond strength rehearsal, to a crosshead speed of 0,5 mm/min. The obtained results were submitted to the variance analysis, and to the test of Tukey, at the level of 5% of significance. It was observed that there was influence of the agents dessensitizers, when these were applied in the bovine dentin and interagiam with the adhesive systems, and G. H. F. Dessensitizer increased statistically the values of resistance of union of Single Bond, and of the it Prime & Bond 2.1, and Oxagel didn't influence in the values of resistance of union of the tested adhesive systems.
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Ibrahim, Mohamed Asim Yousif. "Co-processing of drugs and co-crystal formers and its effect on pharmaceutical dosage-form performance : co-crystallization of urea/2-methoxybenzamide, caffeine/malonic acid, caffeine/oxalic acid and theophylline/malonic acid systems : solid-state characterization including imaging, thermal, X-ray and Raman spectroscopic techniques with subsequent evaluation of tableting behaviour." Thesis, University of Bradford, 2008. http://hdl.handle.net/10454/12760.
Full textAbstract:
This dissertation has focused on the solid-state characterization of different co-crystal system as well as the effect of co-crystallization of these systems on pharmaceutical dosage form performance. Urea/ 2-MB, caffeine/ malonic acid, caffeine/ oxalic acid and theophylline/ malonic acid co-crystals were prepared using co-grinding- and co-precipitation techniques. In addition, the synthesis of co-crystals through two novel methods has been demonstrated. This includes compaction and convection mixing. The solid-state characterization of the co-crystals has been carried out using XRPD, Raman spectroscopy, DSC, TGA, hot-stage microscopy and SEM. After preparation of co-crystals, tablets have been produced from co-ground-, co-precipitated-, and physical mixtures using Compaction Studies Press (Kaleva), and the data were recorded to compare between the different mixtures, regarding compactibilty, compressibility and deformational properties. The DSC results showed that the physical mixtures of all systems, formed co-crystals during heating process. For systems of urea/ 2-MB, caffeine/ malonic acid and theophylline/ malonic acid, the co-ground mixture produced tablets with higher tensile strength compared with either co-precipitated or physical mixture. However, for caffeine/ oxalic acid system, the tensile strengths of compacts produced from the physical mixture were greater than those obtained from either co-ground or co-precipitated mixtures. The Heckel data suggested that urea/ 2-MB, caffeine/ malonic acid and theophylline/ malonic acid systems are Type 1 materials, as an extensive linearity during compression was indicative of a plastic deformation mechanism, while the caffeine/ oxalic acid system was Type 2 materials. However, the co-precipitated mixture of urea/ 2-MB system was the least compressible, as it possessed the greatest value of yield pressure (85 MPa) and the highest elastic recovery (7.42%). The co-precipitated mixture of both of caffeine/ malonic acid and theophylline/ malonic acid systems was the most compressible with small yield pressure values of (44 & 80 MPa) and elastic recovery of (7.2% & 6.56%), respectively. The co-ground mixture of caffeine/ oxalic acid possessed the highest value of yield pressure (166 MPa) and thus the lowest compressibility among other mixtures. Furthermore, the addition of microcrystalline cellulose and α-lactose monohydrate has affected the crystallinity as well as the tableting properties of the co-crystals. After the addition of excipients, the tensile strength of compacts was about 2 times higher than any other mixture. Finally, urea/ 2-MB and caffeine/ malonic acid co-crystals were successfully synthesized through convection mixing and compaction.
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Fernandes, João Roberto. "Metodologias analiticas enzimaticas para analise de oxalato em amostras de interesse biologico." [s.n.], 1996. http://repositorio.unicamp.br/jspui/handle/REPOSIP/250393.
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Orientadores: Graciliano de Oliveira Neto, Matthieu TubinoTese (doutorado) - Universidade Estadual de Campinas, Instituto de Quimica
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Doutorado
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Upadhyay, Swapna [Verfasser], Johannes G. [Akademischer Betreuer] Filser, Erich F. [Akademischer Betreuer] Elstner, and Michael [Akademischer Betreuer] Schemann. "Bioavailability of ethylene glycol and its metabolites glycolic acid and oxalic acid in volunteers following inhalation and dermal exposure to ethylene glycol / Swapna Upadhyay. Gutachter: Erich F. Elstner ; Michael Schemann. Betreuer: Johannes G. Filser." München : Universitätsbibliothek der TU München, 2006. http://d-nb.info/1054345775/34.
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Zhang, Shuo. "Physical properties and crystallization of theophylline co-crystals." Licentiate thesis, KTH, Transport Phenomena, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-13255.
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This work focuses on the physical properties and crystallization of theophyline co-crystals. Co-crystals of theophylline with oxalic acid, glutaric acid and maleic acid have been investigated.
The DSC curves of these co-crystals show that their first endothermic peaks are all lower than the melting temperature of theophylline. The decomposition temperature of theophylline – oxalic acid co-crystal is at about 230 °C, determined by DSC together with TGA. After decomposition, the remaining theophylline melts at about 279 °C, which is higher than the known melting temperature of theophylline, suggesting a structure difference, ie. a new polymorph may have been formed. The formation of hydrogen bonds in theophylline – oxalic acid co-crystal was investigated by FTIR. Changes of FTIR peaks around 3120 cm-1 reflects the hydrogen bond of basic N of theophylline and hydroxyl H of oxalic acid. The solubility of theophylline – oxalic acid co-crystal and theophylline – glutaric acid co-crystal was determined in 4:1 chlroform – methanol and in pure chloroform respectively. At equilibrium with the solid theophylline – oxalic acid co-crystal, the theophylline concentration is only 60 % of the corresponding value for the pure solid theophylline. At equilibrium with the solid theophylline – glutaric acid co-crystal, the theophylline concentration is at least 5 times higher than the corresponding value for the pure solid theophylline. Two phases of theophylline were found during the solubility determination. In the chloroform – methanol mixture (4:1 in volume ratio) the solubility of the stable polymorph of theophylline is found to be about 14 % lower than that of the metastable phase. Various aspects of the phase diagram of theophylline – oxalic acid co-crystal was explored.
Theophylline – oxalic acid co-crystal has been successfully prepared via primary nucleation from a stoichiometric solution mixture of the two components in chloroform – methanol mixture. By slurry conversion crystallization, the co-crystal can be prepared in several solvents, and yield and productivity can be significantly increased. Theophylline – glutaric acid can be successfully prepared via both co-grinding of the two components and slow evaporation with seeding.
QC20100608
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Forti, Juliane Cristina. "Aplicação de eletrodos de óxidos ativados em eletrooxidação orgânica: oxidação de formaldeído, acetaldeído e ácido oxálico." Universidade de São Paulo, 2005. http://www.teses.usp.br/teses/disponiveis/59/59138/tde-23012007-151800/.
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Este trabalho apresenta a preparação e caracterização de eletrodos de óxidos do tipo ânodos dimensionalmente estáveis (ADE) de composição nominal Ti/Ru0,3Ti0,7O2, modificados pela adição de metais em sua superfície. A introdução de um metal modulador permitiu alterar de forma significativa o comportamento eletroquímico de todo o recobrimento. A modificação do ADE foi realizada através de eletrodeposição de Pt e PbO2 e de deposição química de catalisadores nanodivididos (Pt e Pt-Ni). O objetivo desta preparação foi modular as propriedades dos ânodos visando melhorar as propriedades eletrocatalíticas e a resistência mecânica e com isto, introduzir uma nova classe de materiais para aplicá-los na eletrooxidação de formaldeído, acetaldeído e ácido oxálico. Para caracterizar os eletrodos foram utilizadas as técnicas de microscopia eletrônica de varredura (MEV), espectroscopia de energia dispersiva de raios X (EDX), voltametria cíclica (VC), eletrólises com acompanhamento por cromatografia líquida de alta eficiência (CLAE), espectrometria de massas eletroquímica diferencial (DEMS). Os experimentos com DEMS foram realizados na Universidade de Poitiers, França. As micrografias e as análises de EDX mostraram que o rutênio concentra-se em pequenas ?ilhas? na camada de óxidos e a modificação com platina, eletrodepositada ou depositada quimicamente, ocorre preferencialmente nas regiões ricas em rutênio. O eletrodepósito de PbO2 apresentou uma distribuição mais uniforme sobre toda a camada de óxido. As eletrólises foram realizadas aplicando um programa de pulsos de potenciais. Os resultados mostraram que a eficiência para formação do produto mais oxidado (CO2) está intimamente ligada à quantidade e distribuição da platina adicionada na superfície do ADE. Os eletrodos mais eficientes foram os de composições nominais: Ti/ADE modificado com eletrodeposição de Pt (100 ?g cm-2) e Ti/ADE modificado com deposição química do catalisador nanodividido de Pt-Ni (1:1) (60 ?g cm-2). Estes resultados foram confirmados pelos experimentos utilizando DEMS. O eletrodo Ti/ADE modificado com eletrodeposição de PbO2 (100 ?g cm-2) apresentou uma melhora na eficiência eletrocatalítica em relação ao ADE, porém inferior aos eletrodos modificados com platina. O desempenho do ADE na oxidação das pequenas moléculas orgânicas foi estudado em comparação com um eletrodo de platina eletrodepositada diretamente na placa de titânio. Os resultados de eletrólise mostraram que o ADE não funciona somente como um substrato inerte e sim auxilia na reação de oxidação, desempenhando um importante papel na eficiência catalítica total destes materiais.This work presents the preparation and characterization of dimensionally stable anodes (DSA) of nominal composition Ti/Ru0.3Ti0.7O2, modified by the addition of metals to their surface. The introduction of the modulator metal allowed us to change the coating of the electrochemical behavior in a significant way. The DSAâ surface was modified by electrodeposition of Pt and PbO2, and chemical deposition of highly nanodispersive supported catalysts (Pt and Pt-Ni). The objective of this preparation was to modulate the anode properties in order to enhance the electrocatalytic properties and mechanical resistance of these materials. This new class of materials was applied in the electrooxidadtion of formaldehyde, acetaldehyde and oxalic acid. The electrode characterization was carried out by Scanning Electron Microscopy (SEM), Energy-dispersive X-ray Spectroscopy (EDS), cyclic voltammetry (CV), long-term electrolysis followed by high performance liquid chromatography (HPLC) and the differential electrochemical mass spectrometry (DEMS) which was performed at the University of Poitiers, France. The micrographs and EDS analyses showed that the ruthenium is concentrated in small ?islands? in the oxide layer, and the modification with platinum, either electrodeposited or chemically deposited, occurs preferable over the ruthenium-rich regions. The PbO2 electrodeposit was more uniformly distributed along the oxide layer. Bulk electrolysis experiments were carried out applying a potentiostatic program. The efficiency toward the formation of the more oxidized compound (CO2) is related with the amount and distribution of the platinum deposited on the DSAâ surface. The most efficient materials were: Ti/ADE modified with electrodeposited Pt (100 ?g cm-2) and Ti/ADE modified with chemically deposited Pt-Ni (1:1) (60 ?g cm-2). Through the DEMS experiments these results were confirmed. The DSAâ modified with PbO2 (100 ?g cm-2) was more efficient than the bare DSAâ. However, the amount of CO2 obtained with the former electrode is still lower than that obtained with the platinum-modified ones. The role of DSAâ on the direct activation of the oxidation of small organic molecules was studied applying an electrode containing the platinum directly electrodeposited over the titanium. The bulk electrolysis results showed that DSAâ is not just an inert substrate since it does play an important role in the overall efficiency of these materials.
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Lima, Darlon Martins. "Avaliação da resistência de união de diferentes sistemas adesivos à dentina bovina : influência de agentes dessensibilizantes /." Araraquara : [s.n.], 2005. http://hdl.handle.net/11449/89648.
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Orientador: Maria Salete Machado CândidoBanca: José Roberto Cury Saad
Banca: Patricia dos Santos Jardim
Resumo: O objetivo deste trabalho foi o de avaliar comparativamente "in vitro", a resistência de união ao cisalhamento de uma resina composta à dentina bovina em função da combinação de três diferentes sistemas adesivos e de dois diferentes agentes dessensibilizantes. Foram utilizados os sistemas adesivos: Single Bond, Master Bond e Prime & Bond 2.1 e os seguintes agentes dessensibilizantes: o Oxagel e o G. H. F. Dessensibilizador. Para a confecção dos corpos de prova, 90 incisivos bovinos (n=10) foram utilizados, os quais tiveram suas superfícies vestibulares desgastadas, até a exposição dentinária, de tal forma que, a área de adesão padronizada, tivesse 4 mm de diâmetro. Após a realização dos tratamentos de superfície, onde os Grupos controle eram indicados apenas pela aplicação do sistema adesivo, e os Grupos experimentais, pela aplicação dos agentes dessensibilizantes testados após o condicionamento ácido, foram confeccionados cilindros de resina composta Z-100, com o auxílio de uma matriz bipartida. Os corpos-de-prova foram então armazenados em água destilada a 37°C por 24 horas, e submetidos em seguida ao ensaio de cisalhamento, a uma velocidade do atuador de 0,5 mm/min. Os resultados obtidos foram submetidos à análise de variância, e ao teste de Tukey, ao nível de 5% de significância. Observou-se que houve influência dos agentes dessensibilizantes, quando estes eram aplicados na dentina bovina e interagiam com os sistemas adesivos, sendo que o G. H. F. Dessensibilizador aumentou estatisticamente os valores de resistência de união do Single Bond, e do Prime & Bond 2.1, e o Oxagel não influenciou nos valores de resistência de união dos sistemas adesivos testados.
Abstract: The objective of this work was it of evaluating "in vitro" comparatively , the shear bond strength of a resin composed to the bovine dentin in function of the combination of three different adhesive systems and of two different agents dessensitizers. The adhesive systems were used, to know: Single Bond, Master Bond and Prime & Bond 2.1 and the following agents dessensitizers: Oxagel and G. H. F. Desensitizer. For the making of the test bodies, 90 incisive bovine (n=10) they were used, which had its worn away vestibular surfaces, until the exhibition dentin, in such a way that, the area of standardized adhesion, had 4 diameter mm. After the accomplishment of the surface treatments, where the Groups control was just suitable for the application of the adhesive system, and the experimental Groups, for the application of the agents dessensitizers tested after the acid conditioning, cylinders of composed resin were made Z-100, with the aid of a bipartite matrix. The test bodies, they were stored then in water distilled for 37°C by 24 hours, and submitted soon after to the shear bond strength rehearsal, to a crosshead speed of 0,5 mm/min. The obtained results were submitted to the variance analysis, and to the test of Tukey, at the level of 5% of significance. It was observed that there was influence of the agents dessensitizers, when these were applied in the bovine dentin and interagiam with the adhesive systems, and G. H. F. Dessensitizer increased statistically the values of resistance of union of Single Bond, and of the it Prime & Bond 2.1, and Oxagel didn't influence in the values of resistance of union of the tested adhesive systems.
Mestre
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Mendes, Andre Aguiar. "Importância dos mediadores de baixa massa molar na biodegradação de madeira por Ceriporiopsis subvermispora." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/97/97131/tde-20092012-122707/.
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O fungo de podridão branca Ceriporiopsis subvermispora é seletivo na degradação de lignina em estágios curtos de colonização de madeira e dessa forma tem sido uma das espécies mais estudadas em biopolpação, que consiste em um tratamento biológico de cavacos de madeira que antecede etapas convencionais de polpação. Para degradar a lignina na parede celular vegetal esse fungo secreta a enzima manganês-peroxidase (MnP), a qual necessita de ácido oxálico para transportar o íon Mn3+ oriundo do seu ciclo catalítico. O complexo quelante-Mn3+ gerado degrada apenas porções fenólicas da lignina. Porém, por meio da peroxidação de lipídeos por Mn3+, radicais livres são gerados e apresentam potencial de oxidação suficiente para degradar estruturas não-fenólicas da lignina. Com base nesses aspectos, o presente trabalho avaliou a importância desses mediadores da MnP, ácido oxálico e lipídeos, no processo degradativo quanto à adição ou à supressão dessas substâncias nos cultivos. Em cultivos com madeira in natura ou extraídas com etanol (provavelmente isento de lipídeos) não ocorreu diferença significativa quanto à produção de metabólitos extracelulares (enzimas, ácido oxálico), à degradação de lignina e à atividade redutora de Fe3+ (envolvida na geração de radicais OH pela reação de Fenton). A formação de TBARS (substâncias que reagem com o ácido tiobarbitúrico), que serve como indício de reações de peroxidação de lipídeos, também foi semelhante, demonstrando que mesmo a partir de madeira livre de extrativos essas reações ocorrem. Com o avanço do biotratamento, a lignina foi despolimerizada por meio da diminuição de ligações ?-O-4, os teores de OH alifáticas e fenólicas foram diminuídos, enquanto o teor de grupos carboxila aumentou. Embora a degradação de celulose em madeira tenha sido baixa, cartões de holocelulose (livres de lignina) adicionados nesses cultivos foram despolimerizados. Nos cultivos em que houve a adição de uma fonte extra de lipídeos (óleo de soja), a produção de enzimas e degradação de lignina foram similares, enquanto a produção de ácido oxálico e TBARS foi estimulada por esse co-substrato. A maior concentração de óleo de soja adicionado (10,4 g/kg de madeira) fez com que a lignina presente na madeira residual apresentasse o mesmo teor de ligações ?-O-4 que o controle, enquanto maior degradação de OH alifáticas e menor formação de grupos carboxila foram observadas nessas ligninas. Em outro ciclo de cultivos, íons Ca2+ foram adicionados para precipitar o ácido oxálico produzido pelo fungo. Nos cultivos com a mais alta carga de cálcio (1400 mg/kg) houve diminuição na formação de ácido oxálico e consequentemente uma inibição na degradação de todos os componentes da madeira. Ao serem realizados cultivos com ácido oxálico exógeno, o fungo atuou de forma a igualar a concentração de ácido oxálico livre em relação a um cultivo sem esse suplemento, tanto por catabolismo quanto por precipitação desse ácido. Para as máximas cargas de cálcio, ácido oxálico e óleo de soja foram realizados outros cultivos sobre madeira em biorreatores para realização de ensaios de polpação. A polpação quimiotermomecânica sulfito alcalino dessas amostras de madeira biodegradada mostrou que os cultivos adicionados de Ca2+ e os não suplementados foram os que proporcionaram os maiores benefícios atribuídos ao biotratamento. Por outro lado, a adição de ácido oxálico anulou o benefício oriundo do biotratamento. A busca de correlações entre os níveis de metabólitos extracelulares com os benefícios do biotratamento para a polpação quimiotermomecânica não apresentaram tendências claras que indiquem a relevância de um metabólito em especial. Pelo contrário, aparentemente deve haver um compromisso entre todas as atividades extracelulares para que um determinado benefício seja obtido.The white-rot fungus Ceriporiopsis subvermispora degrades lignin selectively during the initial stages of wood colonization and in this way it has been one of the most studied species in biopulping. This process consists of a biological treatment of wood chips that precedes conventional pulping stages. To degrade lignin in the plant cell wall this fungus secretes the enzyme manganese-peroxidase (MnP), which needs oxalic acid to transport the Mn3+ ion formed in the catalytic cycle of the enzyme. The oxalate-Mn3+ complex degrades only lignin phenolic portions. However, through lipid peroxidation intiated by Mn3+, free radicals are generated and they present enough oxidation potential to degrade nonphenolic lignin structures. With basis in these aspects, the present work evaluated the importance of these mediators of MnP, oxalic acid and lipids, in the degradative process either by their addition or suppression in wood-containing cultures. In cultivations with in natura wood or ethanol extracted wood (probably free of lipids) thre was no significant difference in the production of extracelular metabolites (enzymes, oxalic acid), or in the lignin degradation and the Fe3+-reducing activity (involved in the OH radicals generation by the Fenton´s reaction). The formation of TBARS (thiobarbituric acid reactive substances), that ii indicative of lipid peroxidation reactions, was also similar in both cultivations systems, demonstrating that even starting from extractives-free wood, these reactions can occur. With the progress of the biotreatment, the lignin was depolymerized through the decrease of ?-O-4 bonds, the contents of aliphatic and phenolic OH decreased, while carboxyl groups content increased. Although the cellulose degradation in wood has been low, holocellulose cards (free from lignin) added in these cultures were depolymerized. In the cultures where lipids were added (soy-bean oil), the enzyme production and lignin degradation were similar, while the oxalic acid and TBARS productions was stimulated by this co-substrate. With the highest concentration of soy-bean oil added (10,4 g/kg wood), the lignin in the residual wood presented the same content of ?-O-4 bonds as compared to the control, while higher degradation of aliphatic OH and lower formation of carboxyl groups were observed in these lignins. In another cycle of cultivations, Ca2+ ions were added to precipitate oxalic acid produced by the fungus. In the cultivations with the highest load of calcium (1400 mg/kg) there was a decrease in the oxalic acid formation and consequently an inhibition in the degradation of all the wood components. To the cultivations accomplished with exogenous oxalic acid, the fungus acted to equalize the concentration of free oxalic acid either by catabolism or by precipitation of this acid. For the highest loads of calcium, oxalic acid andsoy-bean oil, other cultivations were accomplished on 20 L-biorreactors to produce biotreated wood samples suitable for pulping experiments. The alkaline-sulfite chemitermomechanical pulping of these samples showed that the biotreated wood in Ca2+-ammended and nonsupplemented cultures were the ones that provided the highest benefits. On the other hand, the oxalic acid addition annulled the benefit originated from the biotreatment. The search for correlations among the levels of extracelular metabolites with the benefits of the biotreatment for the chemitermomechanical pulping did not present clear tendencies to indicate the relevance of a metabolite in special. On the contrary, probably there is a commitment among all of the extracellular activities, so that a certain benefit would be obtained.
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Sartori, Neimar. "Avaliação clínica do uso de um agente dessensibilizante no controle da sensibilidade pós-operatória e no desempenho clínico de restaurações classe v de resina composta." Florianópolis, SC, 2008. http://repositorio.ufsc.br/xmlui/handle/123456789/91064.
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Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências da Saúde. Programa de Pós-graduação em OdontologiaMade available in DSpace on 2012-10-23T18:25:42Z (GMT). No. of bitstreams: 1 264740.pdf: 1289011 bytes, checksum: 8e3295514ee069e23f657867c7117ab8 (MD5)
Este estudo teve por objetivo avaliar a sensibilidade pós-operatória e o desempenho clínico de restaurações de resina composta em lesões cervicais não-cariosas (LCNC), com ou sem o uso de agente dessensibilizante à base de oxalato de potássio, por 18 meses. Foram restauradas 144 lesões em 42 pacientes selecionados de acordo com os critérios de inclusão e exclusão estabelecidos, sendo divididos aleatoriamente em quatro grupos: no grupo 1 (G1) as lesões foram restauradas utilizando-se o agente dessensibilizante à base de oxalato de potássio (BisBlock, Bisco, EUA) após o condicionamento ácido e previamente à aplicação do sistema adesivo Adper Single Bond 2 (3M ESPE, EUA). O grupo 2 (G2) foi restaurado com o mesmo sistema adesivo do G1, porém sem a aplicação do agente dessensibilizante. O grupo 3 (G3) foi restaurado utilizando-se o agente dessensibilizante (BisBlock, Bisco, EUA) após o condicionamento ácido e previamente à aplicação do sistema adesivo One-Step (Bisco, EUA). O grupo 4 (G4) foi restaurado com o mesmo sistema adesivo do G3, porém sem a aplicação do agente dessensibilizante. As resinas compostas utilizadas foram: Filtek Supreme (3M ESPE, EUA) no G1 e no G2; e Aelite (Bisco, EUA) no G3 e no G4. As 140 restaurações foram avaliadas por dois examinadores em cinco períodos distintos: inicial, 2, 6, 12 e 18 meses, seguindo os critérios USPHS modificados. Os dados foram submetidos ao teste estatístico de McNemar para verificar possíveis alterações do índice Alfa dentro dos grupos ao longo do tempo. Para analisar a associação entre os grupos em cada momento, utilizou-se o teste Qui-quadrado. Para todos os critérios estudados adotou-se o nível de 5% de significância. Os resultados revelam que não há diferença estatística entre os grupos restaurados com o agente dessensibilizante em comparação aos grupos controle nos critérios sensibilidade relatada, sensibilidade estimulada e retenção das restaurações ao longo do tempo.
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Oliveira, Marcelo de. "Investigação do ácido etanodióico na formação de filmes superficiais sobre zinco e avaliação do efeito destes filmes na resistência à corrosão." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-19022018-101642/.
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Um dos métodos mais utilizados para proteção contra a corrosão de aços comuns consiste na proteção catódica com revestimentos metálicos eletroquimicamente mais ativos, que estes. Os revestimentos de zinco são os mais usados para este tipo de proteção. De forma a protegerem o substrato, estes revestimentos devem atuar como anodos de sacrifício, sofrendo corrosão e transformando o substrato de aço em catodo. Todavia, não é de interesse, que o revestimento de zinco apresente altas taxas de corrosão de forma que a proteção contra a corrosão conferida ao aço seja duradoura. Uma das formas mais empregadas para reduzir a velocidade de corrosão do revestimento de zinco é por meio de tratamentos da superfície, por exemplo, por tratamentos de conversão. Os tratamentos de conversão mais eficientes são os que utilizam e geram rejeitos, que contêm íons de cromo hexavalente. Todavia, estes íons são carcinogênicos e tóxicos e, dessa forma, os processos que os utilizam em alguma etapa do tratamento, vêm sofrendo crescentes restrições, já sendo proibidos em países com leis ambientais mais rígidas. Esta é a razão para o crescente interesse e grande investimento em pesquisa tratamentos, que possam resultar em revestimentos com potencialidade para substituir, de forma eficiente e efetiva o uso do cromo hexavalente. Este foi o objetivo do presente trabalho. Neste estudo, foi investigado o efeito de tratamentos, que resultam em camadas de conversão na presença de ácido oxálico e na proteção contra a corrosão da superfície do zinco. Camadas de conversão foram obtidas por imersão de amostras de zinco em soluções de ácido oxálico (ácido etanodióico) com diferentes concentrações. Todas as soluções de tratamento apresentaram elevada acidez e resultaram em ataque da superfície de zinco com formação de revestimento de conversão com diferentes características. Ensaios preliminares de névoa salina foram então realizados para investigar a proteção conferida pelo sistema revestimento de conversão-verniz contra a corrosão do substrato de zinco. Estes ensaios foram decisivos para a escolha da faixa de concentração do banho de conversão com maior potencial para formação de revestimentos de conversão protetores. Os resultados deste ensaio e os de espectroscopia de impedância eletroquímica mostraram que tratamentos em soluções com composição superiores a 10-1 M de ácido oxálico resultaram em camadas muito defeituosas, nas quais o ataque localizado do substrato metálico é favorecido, sendo obtidas impedâncias menores que a superfície do zinco sem qualquer tratamento. Os resultados de XPS mostraram, que os revestimentos de conversão formados em soluções de ácido oxálico na faixa de 10-3 M a 10-1 M são compostos de oxalato de zinco e produtos de corrosão do zinco, especificamente ZnO, Zn (OH)2, e ZnCO3. Já a concentração de 10-1 M de ácido oxálico foi a, que produziu os resultados mais promissores com a formação de um revestimento, que conferiu proteção mais duradoura à superfície do zinco entre os obtidos. As espessuras médias das camadas de conversão de oxalato de zinco formadas em soluções com 10-1 M e 1 M de ácido oxálico, estimadas por FIB, foram respectivamente 600 nm e 300 nm, o que mostra que a concentração de 1 M de ácido causou intenso ataque corrosivo da superfície, enquanto a camada formada em meio com 10-1 M permitiu a deposição de camada mais espessa e mais protetora contra a corrosão do substrato. Os resultados de XPS indicaram a degradação da camada de oxalato de zinco com o tempo de ensaio, porém o ataque desta ao longo do ensaio de corrosão, resulta na formação de simonkolleite, identificada por difração de raios X, para períodos mais longos do ensaio de corrosão, no caso do revestimento formado em solução com 10-1 M em comparação a 1M. A simonkolleite atua por efeito barreira bloqueando os defeitos/porosidade da camada. O crescente acúmulo destes produtos de corrosão com a continuidade do processo corrosivo e a aderência destes ao substrato metálico foi indicada para superfície tratada em solução com 10-1 M de ácido oxálico. Finalmente, foi proposto um modelo para interação entre o revestimento de conversão de oxalato de zinco e os produtos de corrosão em que a retenção dos produtos de corrosão na superfície faz com, que a camada na superfície se torne mais espessa e mais compacta com o tempo de exposição ao ensaio de corrosão. Estas observações explicam o aumento de impedância observado com o tempo de ensaio nesta condição. Os resultados obtidos permitiram concluir, que o revestimento de conversão de oxalato de zinco formado em solução com 10-1 M de ácido oxálico resulta em proteção efetiva do substrato metálico além de apresentar boa aderência com camada de verniz. Estes resultados indicam potencialidade deste tratamento como preparação de superfícies de zinco, que serão recobertas com revestimentos orgânicos (tintas, vernizes ou lacas).One of the most used methods for protection of common steels is the cathodic protection by galvanic coupling with metallic coatings electrochemically more active than these. Zinc coatings are the most commonly used for this type of protection. In order to protect the metallic substrate, these coatings must act as sacrificial anodes, corroding themselves and converting the steel substrate into cathode. However, it is not appropriate that the zinc coating presents high corrosion rates, so that the corrosion protection conferred to the steel is long-lasting. One of the most commonly employed methods of reducing the corrosion rate of zinc coatings is by surface treatments, such as, conversion treatments. The most efficient conversion treatments to date are those that use hexavalent chromium ions or generate residues containing these ions. However, hexavalent chromium is carcinogenic and toxic and, therefore, the processes that involve their use at some stage of the treatment, are under increasing restrictions, and have already been prohibited in developed countries. This is the reason for the growing interest and great investment in research studies in search for treatments that may result in coatings with the potential to efficiently and effectively replace the use of hexavalent chromium. This was the objective of the present study. In this study, the effect of treatments in oxalic acid solutions that resulted in conversion layers on the corrosion protection of zinc surface has been investigated. Conversion layers were obtained by immersion of zinc samples in solutions of oxalic acid (ethanedioic acid) with different concentrations. All the treatment solutions presented high acidity and resulted in attack of zinc surface and formation of conversion coatings of different characteristics. A layer of varnish was applied and preliminary salt spray tests were then carried out to investigate the corrosion protection provided by the system conversion coating -varnish to the zinc substrate. These tests were decisive for the choice of the conversion bath composition range with greater potentialities for the formation of protective conversion coatings. The results of the salt spray test and of electrochemical impedance spectroscopy (EIS) showed that treatments in solutions with compositions greater than 10-1 M of oxalic acid resulted in very defective conversion layers in which the localized attack of the metallic substrate is favored, and lower impedances than the zinc surface without any treatment were obtained for surfaces treated in these solution. The XPS results showed that conversion coatings formed in oxalic acid solutions in the range of 10-3 M to 10-1 M are composed of zinc oxalate and zinc corrosion products, specifically ZnO, Zn (OH)2, and ZnCO3. The concentration related to the most promising results was 10-1 M and in this solution, the coating formed that promoted the longer lasting protection of the zinc surface among those obtained. The average thicknesses of the zinc oxalate conversion layers formed in solutions with 10-1 M and 1 M of oxalic acid, estimated by FIB, were respectively 600 nm and 300 nm. This result showed that in 1 M of oxalic acid an intense corrosive attack of the zinc surface occurred, while the layer formed in 10-1 M was thicker and more protective against substrate corrosion. The XPS results indicated degradation of the zinc oxalate layer formed in 10-1 M solution with time of exposure to the test solution, but for the protection of the coating lasted for longer periods, comparatively to that formed in 1M solution, once the attack of the first film resulted in formation of simonkolleite, which was identified by X-ray diffraction. Simonkolleite acts by barrier effect blocking defects / porosity in the conversion layer. The increasing accumulation of corrosion products with test time and their adhesion to the metallic substrate was indicated for surface treated in solution with 10-1 M of oxalic acid. Finally, a model has been proposed for the interaction between the zinc oxalate conversion coating and the corrosion products in which the retention of these products on the surface is promoted by the conversion coating and the surface layer becomes thicker and more compact with time of exposure. These observations explain the increased impedance observed with the test time associated to this coating. The obtained results allowed concluding that the conversion coating of zinc oxalate formed in solution with 10-1 M of oxalic acid results in effective protection of the metallic substrate besides promoting good adhesion with a layer of varnish. These results indicate the potential of this treatment as preparation of zinc surfaces that will be covered with organic coatings (paints, varnishes or lacquers).
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Ferreira, Murilo de Souza. "Variabilidade espacial e temporal da reaeração superficial em riachos: estimativa por meio dos métodos do traçador gasoso e da sonda solúvel flutuante." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/18/18138/tde-20062018-145344/.
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A reaeração superficial é um importante fenômeno físico responsável pela transferência de massa do oxigênio atmosférico para o curso de água, através da interface ar-água. Esse fenômeno é caracterizado quantitativamente pelo coeficiente de reaeração superficial (K2). O K2 pode ser influenciado por diversos fatores naturais, em especial, a turbulência, que é afetada pelas características físicas, hidrológicas e hidráulicas do escoamento da água. Este coeficiente é comumente utilizado em modelos ambientais de qualidade da água, o que implica na necessidade da sua correta estimativa. A estimativa do K2 pode ser realizada por meio de métodos e modelos de predição, entre os métodos destacam-se o traçador gasoso e a sonda solúvel flutuante. O objetivo principal desta pesquisa foi verificar a variabilidade espacial e temporal do K2 em cinco trechos de quatro riachos tropicais localizados no município de São Carlos-SP, em um ano de amostragem. Nesses trechos foram mensuradas as principais variáveis químicas, físicas, hidrológicas e hidráulicas do escoamento da água, além do K2 e a velocidade de dissolução de uma sonda solúvel flutuante (VS). A estimativa do K2 ocorreu pelo método do traçador gasoso, sendo o SF6 e o NaCl os traçadores utilizados. A estimativa do VS ocorreu pelo método da sonda solúvel flutuante, confeccionada com ácido oxálico dihidratado e no formato esférico. Análises estatísticas de correlação (Spearman, r) e variância (Kruskal-Wallis) foram realizadas, e modelos de regressão linear simples (RLS) e múltipla (RLM) foram desenvolvidos. Os trechos apresentaram profundidades e larguras médias inferiores a 0,42 m e 3,27 m, respectivamente. A vazão e a velocidade (U) média variaram de 0,001 m3.s-1 a 0,110 m3.s-1 e de 0,01 m.s-1 a 0,33 m.s-1, respectivamente. Os números de Reynolds e Froude (Fr) foram inferiores a 34070 e 0,36, respectivamente. Os K2 variaram de 16,90 dia-1 a 373,80 dia-1 e os VS, de 0,08 mm.min-1 a 0,77 mm.min-1. Os resultados demonstraram variação espacial significativa e temporal não significativa para as variáveis físicas, hidrológicas, hidráulicas, e também para o K2 e VS. U e Fr foram as principais variáveis que se correlacionaram com o K2 (r > 0,68). Um adequado modelo RLM de predição do K2 (R² = 0,75), baseado em todas as variáveis físicas, hidrológicas e hidráulicas e no VS, foi obtido. O modelo RLS, baseado apenas na relação entre K2 e VS, não foi adequado (R² = 0,43) para a predição do K2. A razão entre os fenômenos da reaeração superficial e dissolução da sonda solúvel flutuante não foi constante, e foi afetada pela turbulência na interface ar-água, o que indicou que o método da sonda solúvel flutuante ainda precisa ser aprimorado. Espera-se que, além de gerarem dados sobre um método (sonda solúvel flutuante) e tema (reaeração superficial) ainda relativamente pouco estudados em riachos tropicais, as informações apresentadas sobre as principais variáveis intervenientes no fenômeno de reaeração superficial e dissolução em riachos possam oferecer direcionamentos a estudos ambientais, especialmente àqueles que versam sobre a qualidade dos recursos hídricos.Surface reaeration is an important physical phenomenon responsible for the transfer of atmospheric oxygen mass into the water course through the air-water interface. This phenomenon is quantitatively characterized by the surface reaeration coefficient (K2). K2 can be influenced by several natural factors, especially turbulence, which is affected by the physical, hydrologic and hydraulic characteristics of the watercourse. This coefficient is commonly used in environmental models of water quality, which implies the need for its correct estimation. The estimation of K2 can be performed by models of prediction and methods, among the methods the gas tracer and the floating soluble probe stand out. The aim of this research was to verify the spatial and temporal variability of K2 in five stretches of four tropical streams located in the city of São Carlos-SP, in a year of sampling. In these stretches the main chemical, physical, hydrological and hydraulic variables of the watercourse were measured, besides K2 and the dissolution rate of the floating soluble probe (VS). The estimation of K2 occurred by the gas tracer method, with SF6 and NaCl being the tracers used. The VS estimation was carried out by the floating probe method, made with oxalic acid dihydrate and in spherical format. Statistical analyzes of correlation (Spearman, r) and variance (Kruskal-Wallis) were performed, and simple linear regression (SLR) and multiple linear regression models (MLR) were developed. The stretches presented mean depths and widths of less than 0.42 m and 3.27 m, respectively. The flow rate and average velocity (U) ranged from 0.001 m3 s-1 to 0.110 m3s-1 and from 0.01 m.s-1 to 0.33 m.s-1, respectively. The Reynolds and Froude (Fr) numbers were less than 34070 and 0.36, respectively. The K2 ranged from 16.90 day-1 to 373.80 day-1 and the VS, from 0.08 mm.min-1 to 0.77 mm.min-1. The results showed significant spatial variation and a non-significant temporal variation for the physical, hydrological and hydraulic variables, as well as for K2 and VS. U and Fr were the main variables that correlated with K2 (r > 0.68). A suitable MLR prediction model of K2 (R² = 0.75), based on all physical, hydrological and hydraulic variables and VS, was obtained. The SLR model, based only on the relationship between K2 and VS, was not adequate (R² = 0.43) for K2 prediction. The ratio between the phenomena of surface reaeration and dissolution of the floating soluble probe was not constant and was affected by turbulence at the air-water interface, which indicated that the floating soluble probe method still needs to be improved. It is expected that, in addition to generating data on a method (floating soluble probe) and surface (surface reaeration) that are still relatively little studied in tropical streams, the information presented on the main variables involved in the phenomenon of surface reaeration and dissolution in streams may offer environmental studies, especially those dealing with the quality of water resources.
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Hriczo, Filip. "Vliv změny vstupních parametrů na výrobu nanoporézní keramiky." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2010. http://www.nusl.cz/ntk/nusl-218572.
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This thesis examines and tests acids and conditions, which make the production of nanoporous ceramic at the thin aluminium layer the most effective and provide the highest quality. This paper describes the production of nanoporous structures with pore size 15-400 nm, depending on the electrolyte. Creating a regular hexagonal structure by electrochemical oxidation is dependent on many parameters that affect the regularity of structure and parameters of the ceramics produced. They were investigated primarily by changes in temperature and input voltage. All results were examined by SEM analysis.
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Hilgert, Leandro Augusto. "Adesão à dentina." Florianópolis, SC, 2006. http://repositorio.ufsc.br/xmlui/handle/123456789/89167.
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Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Ciências da Saúde. Programa de Pós-Graduação em OdontologiaMade available in DSpace on 2012-10-22T17:33:39Z (GMT). No. of bitstreams: 1 226738.pdf: 7998368 bytes, checksum: 9628cbe288784e31e6db5413f4e49dc0 (MD5)
O objetivo deste estudo in vitro foi avaliar a influência da oclusão tubular e da desproteinização dentinária na adesão entre dentina e resina composta. As metodologias utilizadas foram: análise em microscopia eletrônica de varredura (MEV) das superfícies dentinárias tratadas, antes da aplicação do sistema adesivo; teste de resistência de união à microtração; análise em MEV das interfaces resina-dentina formadas; teste de microinfiltração marginal. Conclui-se que a técnica da oclusão tubular não afeta a resistência de união, nem a microinfiltração quando comparada ao protocolo tradicional. A desproteinização, quando não associada à oclusão tubular, pode aumentar a resistência de união e reduzir a microinfiltração.
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Vilela, Rivelino Cunha. "Estudo de transições de fase em cristais de l-alanina + ácido oxálico." reponame:Repositório Institucional da UFC, 2013. http://www.repositorio.ufc.br/handle/riufc/13883.
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VILELA, Rivelino Cunha. Estudo de transições de fase em cristais de l-alanina + ácido oxálico. 2013. 113 f. Tese (Doutorado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2013.Submitted by Edvander Pires (edvanderpires@gmail.com) on 2015-10-29T21:51:24Z No. of bitstreams: 1 2013_tese_rcvilela.pdf: 12577577 bytes, checksum: 4dc32419c1bbdde79375612c04227181 (MD5)
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In the present word we have studied the effect of temperature on the Raman spectra of crystals of L-alanine + oxalic acid, C3H8NO2+.C2HO4-. Raman spectroscopy measurements were performed on polycrystalline samples at different temperatures varying in the range from room temperature to T = 20 K; a tentative assignment of all normal modes was furnished. In order to help the understanding of the crystal behavior we have also obtained X-ray diffractograms and studied the dependence of lattice parameters through dilatometry as a function of temperature in the 290 K – 93 K range. The three different techniques allowed us to construct a picture of the material under low temperature conditions. As a consequence we have realized that L-alanine + oxalic acid crystal undergoes three phase transitions at low temperatures. The splitting of a band at 90 cm-1 and an anomaly in one of the lattice parameters are the signature for the first phase transition that is observed at 250 K. At 150 K it was observed the appearance of two new bands in the Raman spectrum and, simultaneously, it was observed change in the curves of a and c lattice parameters. Additionally, it was verified the appearance of new peaks in the X-ray diffractogram at the same temperature, characterizing the second phase transition. At a temperature even lower, at about 43 K, it was verified the occurrence of the third phase transition that has as main characteristic the splitting of two bands that are associated to the lattice modes. Changes in the modes associated with CH3 and NH3+ during the cooling is discussed. An important behavior of the crystal with the cooling process was the red shift of the band of lower frequency, similar to the soft-mode vibration of ferroelectric materials, although the frequency of the mode in L-alanine + oxalic acid does not goes to zero. Based on the results on Raman spectroscopy, dilatometry and X-ray diffraction, and on the possible symmetry sites occupied by the molecules through the O=CC group in the various phases, it is suggested the following sequence of phase transitions D24 C2h5 Cs3 C23, which should occur at 250 K, 150 K and 43 K.
Neste trabalho, estudou-se o efeito da temperatura nos espectros Raman de cristais de L-alanina + ácido oxálico, C3H8NO2+.C2HO4-. Foram realizadas medidas de espectroscopia Raman em policristais a diferentes temperaturas no intervalo compreendido entre a temperatura ambiente e a temperatura de 20 K, sendo fornecida uma identificação tentativa para todos os modos normais de vibração observados. Para auxiliar o entendimento do comportamento do cristal também foram obtidos os difratogramas de raios-X bem como estudada a dependência dos parâmetros de rede em função da temperatura através de dilatometria no intervalo entre 290 K e 93 K. As três técnicas utilizadas em conjunto permitiram mostrar o comportamento estrutural do material em baixas temperaturas. Deste quadro foi possível inferir que os cristais de L-alanina + ácido oxálico apresentam três diferentes transições de fase durante o resfriamento. Em 250 K o aparecimento de um dubleto em 90 cm-1 e a anomalia num dos parâmetros de rede apontam para a ocorrência da primeira transição de fase. Em 150 K surgem pelo menos duas novas bandas no espectro Raman, ao mesmo tempo em que ocorrem bruscas mudanças de inclinação nas curvas que representam as dimensões dos eixos a e c do cristal. Também se verifica que, de forma semelhante ao que ocorre com os espectros Raman, aparecem novos picos no difratograma de raios-X em torno desta temperatura, caracterizando assim a segunda transição de fase. A uma temperatura ainda mais baixa, em torno de 43 K, foi verificada a ocorrência da terceira transição de fase, que tem como principal característica a separação de dois modos Raman associados a modos da rede. Mudanças nos ambientes dos grupos CH3 e do NH3+ durante o resfriamento são discutidas. Um importante aspecto apresentado pelos espectros Raman com o resfriamento da amostra foi o deslocamento da banda de mais baixa energia para menores valores de frequências, semelhantemente ao que ocorre com vibrações do tipo soft-mode em materiais ferroelétricos, embora a frequência do modo no cristal de L-alanina + ácido oxálico não tenha ido à zero. Baseado nos resultados acima e nos possíveis sítios de simetria ocupados pelas moléculas através do grupo O=CC nas diversas fases, sugere-se a seguinte sequência de transições de fase D24 para C2h5 para Cs3 para C23, que aconteceriam, respectivamente, nas temperaturas de 250 K, 150 K e 43 K.
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Gostu, Sumedh. "Investigation Of Chemical Processes For The Production Of Commercially Viable High Volume Value-Added Products From Bauxite Residue." Digital WPI, 2018. https://digitalcommons.wpi.edu/etd-dissertations/531.
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Bayer processing of bauxite employed for production of alumina yield a residue red-mud. The worldwide annual-rate of red-mud generation is approximately 120 million tons, and most of this is stockpiled. Red mud is rich in elements like aluminum, titanium and rare earths, in addition to the major iron-bearing constituents. The objective of this research is to explore such a strategy to extract Iron as fine particulate magnetite. Pyrometallurgical reduction experiments using carbon mixtures and a novel hydrometallurgical route are experimented. Reduction experiments performed with petroleum coke as a reductant resulted in incomplete reduction. The ‘optimal conditionsÂ’ for gaseous state reduction are determined to be: a processing temperature of 540oC ± 10oC, partial pressures CO (g) and CO2 (g) each of 0.070atm (bar) ± 0.001atm.(bar)/ inert diluent-gas: N2 (g), for a conversion-time of 30min. A mathematical-model was developed on the basis of unidirectional-diffusion of CO2 (g) within the CO2 (g)–CO (g)–N2 (g) gas-phase of the porous product-layer. Magnetic separation applied to the optimally reduced sample in: obtaining a magnetic portion with high iron and non-magnetic portion containing nonferrous (Al, Ti) is not successful. This finding was subsequently attributed to the nanometer length-scales crystallites of the predominant iron-containing phase, hydrated ferric-oxide(s) as determined by STEM micrographs. In addition, the presence of substitution for Fe3+ by Al3+ and Ti3+/4+ are determined with the help of MÖssbauer spectrograms. A hydrometallurgical route involving selective leaching and precipitation of iron in red-mud is tried. Red-mud is leached in oxalic acid at: 95˚C, 15 % Pulp density, 2.5 h leaching time, 1.5 pH. Kinetic studies yielded the leaching mechanism to be predominantly fluid film control. Ferric oxalate in the leach liquor is reduced to insoluble ferrous oxalate selectively using Iron powder. The ferrous oxalate formed is ~98 % pure. The precipitated ferrous oxalate is magnetically separated and reduced in Nitrogen atmosphere to form fine particulate magnetite. Additionally an economic feasibility study was conducted for the hydro and pyro alternatives to produce magnetite using Monte Carlo Simulations by imparting uncertainties in various input cost components. A traditional process was also compared to the proposed approaches for Total Capital Investment (TCI), Total Product Cost (TPC), Net Present Value (NPV) and sensitivity analysis. ~52 % reduction in Total product cost, 46 % reduction in Total Capital Investment was achieved for the hydrometallurgical process when compared to the traditional approach.
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Cosway, Sarah M. "Desymmetrization of Meso-epoxides and related structures via Oxazin-2-one generation and modification : a general approach to cyclic and acyclic #alpha#-amino acids." Thesis, University of Reading, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266045.
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Berná, Galiano Antonio. "Estudio espectroelectroquímico de los equilibrios ácido-base de especies adsorbidas sobre electrodos metálicos con superficies monocristalinas bien definidas." Doctoral thesis, Universidad de Alicante, 2014. http://hdl.handle.net/10045/45809.
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Glue, Joshua Barnaby. "Engineering Allium White Rot Disease Resistance in Allium Species and Tobacco Model Species." Thesis, University of Canterbury. School of Biological Sciences, 2009. http://hdl.handle.net/10092/3513.
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Allium white rot (AWR) is a soilborne disease that seriously damages commercial cultivation of onion (Allium cepa) and garlic (Allium sativum) crops. The disease has been found everywhere onions are cultivated and at present no system of control has been found that fully prevents the occurrence of the disease. The fungus responsible for the disease, Sclerotium cepivorum, uses oxalic acid to kill Allium bulb and root tissue in growing onion and garlic plants. Research suggests recombinant oxalate oxidase and oxalate decarboxylase enzymes may be able to degrade this acid and confer resistance against pathogens that rely on it, such as Sm. cepivorum or Sclerotinia sclerotiorum. To test the efficacy of these enzymes against white rot pathogens, three transgenes for wheat oxalate oxidase, barley oxalate oxidase and Flammulina oxalate decarboxylase were transformed into onions and garlic by Agrobacterium-mediated transformation. Allium species are highly recalcitrant to transformation, so these three transgenes were also transformed into tobacco to provide fast-recovering, easy to test transformants to assess the efficacy of the transgenes. Transformed garlic and tobacco lines were analysed to assess the integration and expression of the transgenes, then challenged with Sm. cepivorum or Sa. sclerotiorum, respectively, to assess the bioactivity of recombinant wheat oxalate oxidase, barley oxalate oxidase, and Flammulina oxalate decarboxylase against oxalic acid-dependent pathogens. Results show that one line of tobacco expressing the Flammulina oxalate decarboxylase enzyme was found to be consistently resistant to Sclerotinia sclerotiorum. Garlic lines transformed with this transgene failed to display stable transgene expression or disease resistance, possibly due to silencing of the transgene in recovered transformant tissue.
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Vilela, Rivelino Cunha. "ESTUDO DE TRANSIÃÃES DE FASE EM CRISTAIS DE L-ALANINA + ÃCIDO OXÃLICO." Universidade Federal do CearÃ, 2013. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=10397.
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CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel SuperiorNeste trabalho, estudou-se o efeito da temperatura nos espectros Raman de cristais de L-alanina + Ãcido oxÃlico, C3H8NO2+.C2HO4-. Foram realizadas medidas de espectroscopia Raman em policristais a diferentes temperaturas no intervalo compreendido entre a temperatura ambiente e a temperatura de 20 K, sendo fornecida uma identificaÃÃo tentativa para todos os modos normais de vibraÃÃo observados. Para auxiliar o entendimento do comportamento do cristal tambÃm foram obtidos os difratogramas de raios-X bem como estudada a dependÃncia dos parÃmetros de rede em funÃÃo da temperatura atravÃs de dilatometria no intervalo entre 290 K e 93 K. As trÃs tÃcnicas utilizadas em conjunto permitiram mostrar o comportamento estrutural do material em baixas temperaturas. Deste quadro foi possÃvel inferir que os cristais de L-alanina + Ãcido oxÃlico apresentam trÃs diferentes transiÃÃes de fase durante o resfriamento. Em 250 K o aparecimento de um dubleto em 90 cm-1 e a anomalia num dos parÃmetros de rede apontam para a ocorrÃncia da primeira transiÃÃo de fase. Em 150 K surgem pelo menos duas novas bandas no espectro Raman, ao mesmo tempo em que ocorrem bruscas mudanÃas de inclinaÃÃo nas curvas que representam as dimensÃes dos eixos a e c do cristal. TambÃm se verifica que, de forma semelhante ao que ocorre com os espectros Raman, aparecem novos picos no difratograma de raios-X em torno desta temperatura, caracterizando assim a segunda transiÃÃo de fase. A uma temperatura ainda mais baixa, em torno de 43 K, foi verificada a ocorrÃncia da terceira transiÃÃo de fase, que tem como principal caracterÃstica a separaÃÃo de dois modos Raman associados a modos da rede. MudanÃas nos ambientes dos grupos CH3 e do NH3+ durante o resfriamento sÃo discutidas. Um importante aspecto apresentado pelos espectros Raman com o resfriamento da amostra foi o deslocamento da banda de mais baixa energia para menores valores de frequÃncias, semelhantemente ao que ocorre com vibraÃÃes do tipo soft-mode em materiais ferroelÃtricos, embora a frequÃncia do modo no cristal de L-alanina + Ãcido oxÃlico nÃo tenha ido à zero. Baseado nos resultados acima e nos possÃveis sÃtios de simetria ocupados pelas molÃculas atravÃs do grupo O=CC nas diversas fases, sugere-se a seguinte sequÃncia de transiÃÃes de fase D24 para C2h5 para Cs3 para C23, que aconteceriam, respectivamente, nas temperaturas de 250 K, 150 K e 43 K.
In the present word we have studied the effect of temperature on the Raman spectra of crystals of L-alanine + oxalic acid, C3H8NO2+.C2HO4-. Raman spectroscopy measurements were performed on polycrystalline samples at different temperatures varying in the range from room temperature to T = 20 K; a tentative assignment of all normal modes was furnished. In order to help the understanding of the crystal behavior we have also obtained X-ray diffractograms and studied the dependence of lattice parameters through dilatometry as a function of temperature in the 290 K â 93 K range. The three different techniques allowed us to construct a picture of the material under low temperature conditions. As a consequence we have realized that L-alanine + oxalic acid crystal undergoes three phase transitions at low temperatures. The splitting of a band at 90 cm-1 and an anomaly in one of the lattice parameters are the signature for the first phase transition that is observed at 250 K. At 150 K it was observed the appearance of two new bands in the Raman spectrum and, simultaneously, it was observed change in the curves of a and c lattice parameters. Additionally, it was verified the appearance of new peaks in the X-ray diffractogram at the same temperature, characterizing the second phase transition. At a temperature even lower, at about 43 K, it was verified the occurrence of the third phase transition that has as main characteristic the splitting of two bands that are associated to the lattice modes. Changes in the modes associated with CH3 and NH3+ during the cooling is discussed. An important behavior of the crystal with the cooling process was the red shift of the band of lower frequency, similar to the soft-mode vibration of ferroelectric materials, although the frequency of the mode in L-alanine + oxalic acid does not goes to zero. Based on the results on Raman spectroscopy, dilatometry and X-ray diffraction, and on the possible symmetry sites occupied by the molecules through the O=CC group in the various phases, it is suggested the following sequence of phase transitions D24 C2h5 Cs3 C23, which should occur at 250 K, 150 K and 43 K.
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Sartarelli, Natália Cecília. "Estudo do teor de ácido oxálico em hortaliças e frutos, seu potencial de cristalização in vitro e caracterização morfológica de cristais de oxalato de cálcio." Araraquara, 2018. http://hdl.handle.net/11449/155899.
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Orientador: Luis Vitor Silva do SacramentoBanca: Mary Rosa Rodrigues de Marchi
Banca: Amanda Martins Baviera
Resumo: Objetivos: Analisar quali e quantitativamente algumas hortaliças e frutos, quanto ao teor de ácido oxálico e avaliar o comportamento químico do ácido oxálico frente a agentes indutores e inibidores de cristalização in vitro. Métodos: A análise qualitativa morfológica de cristais de oxalato de cálcio foi feita sob microscopia ótica de luz polarizada e, quantitativamente foram determinados por método espectrofotométrico, os teores de ácido oxálico após extração com água e ácido clorídrico. Foram realizados também ensaios de indução de cristalização com cloreto de cálcio e inibição com sulfato de magnésio e citrato de sódio, respectivamente. Resultados: Foram identificados cristais de oxalato de cálcio do tipo drusas na alface; ráfides no cará e kiwi e, na rúcula e laranja não foi possível identificar o tipo morfológico do cristal presente. No estudo quantitativo observou-se diferença significativa entre as médias obtidas nas extrações aquosa e ácida somente para o cará, sendo superior na extração ácida. Observou-se ainda significância somente para a couve no ensaio quantitativo de cristalização; o acréscimo de sulfato de magnésio como agente inibidor da cristalização não foi significativo para todas as amostras avaliadas no estudo, no entanto, com o acréscimo de citrato de sódio houve aumento do conteúdo de ácido oxálico para o cará, inhame, laranja e kiwi. No estudo qualitativo dos ensaios de cristalização com cloreto de cálcio em microscopia ótica de luz polarizada observou-s... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: Objectives: Analyze qualitatively and quantitatively some vegetables and fruits, regarding in the content of oxalic acid and evaluate the chemical behavior of the oxalic acid against inducers and inhibitors agents of the in vitro crystallization. Methods: The qualitative morphological analysis of calcium oxalate crystals was done under optical microscopy of polarized light and, quantitatively, the values of oxalic acid after extraction with water and hydrochloric acid were determined by spectrophotometric method. Tests inducting the crystallization with calcium chloride and inhibitioning with magnesium sulphate and sodium citrate, respectively, were also performed. Results: Druses calcium oxalate crystals were identified in lettuce; raphides in yam and kiwifruit; and in the arugula and orange it was not possible to identify the morphological type of the present crystal. In the quantitative study a significant difference was observed between the averages obtained in the aqueous and acid extractions only for the yam, being superior in the acid extraction. It was also observed a significance only for the wild cabbage in quantitative crystallization test. The addition of magnesium sulphate as a crystallization inhibitor was not significant for all the samples evaluated in the study. However, with the addition of sodium citrate there was an increase in the content of oxalic acid for yam, taro, orange and kiwifruit. Crystalline arrangements were observed in the qualitative study of crystallization tests with calcium chloride under optical microscopy of polarized light; in the test with magnesium sulphate it was noticed the presence of polyhedral crystals in kiwifruit, wild cabbage and orange and, with the addition of sodium citrate, small crystals were present only in lettuce... (Complete abstract click electronic access below)
Mestre
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Мазанка, Вероніка Михайлівна. "Кулонометричний генератор дiоксиду карбону для створення перевiрочних сумiшей." Master's thesis, КПІ ім. Ігоря Сікорського, 2020. https://ela.kpi.ua/handle/123456789/34820.
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Робота апробована на Всеукраїнському студенському контурсі.Дисертація присвячена дослідженню електрохімічної поведінки електродних матеріалів в розчинах оксалатної кислоти для контрольованого генерування діоксиду карбону з високим виходом за струмом в кулонометричному генераторі, який може бути використаний для перевірки роботоспроможності засобів моніторингу концентрації вуглекислого газу в повітряному середовищі. Показано високу стійкість неіржавної сталі в розчинах оксалатної кислоти за умов катодної поляризації та після вимкнення катодного струму. Досліджено електрокаталітичні властивості оксидів нікелю та олова, отриманих при термічному окисленні і нанесених на титанову та алюмінієву основу. Показано перевагу титанової основи перед алюмінієвою, що пов'язано з її більшою схильністю до пасивації та кращою адгезією до електролітичних покриттів. Створена комірка кулонометричного генератора, де в якості катоду виступає неіржавна сталь, а як анод – суміш оксиду нікелю та стануму нанесених термічним шляхом на титанову основу. Дана конструкція дозволяє отримувати вуглекислий газ з виходом за струмом газу 80 % в широкому діапазоні густин струму впродовж значного терміну експлуатації.
The dissertation is devoted to the study of the electrochemical behavior of electrode materials in solutions of oxalic acid for the controlled generation of dioxide by a coulometric generator, which can be used to test the operability of the means of monitoring the concentration of carbon dioxide in the air. High stability of stainless steel in oxalic acid solutions is demonstrated under cathode polarization and after cathode current shutdown. The electrocatalytic properties of nickel oxides obtained by thermal oxidation and deposited on a titanium and aluminum base were investigated. The advantage of titanium base over aluminum is shown, which is due to its greater tendency to passivation and better adhesion to electrolytic coatings. and tin. A cell of a coulometric generator is created, where stainless steel is used as the cathode and thermally applied on the titanium base as the anode. This design allows the production of carbon dioxide gas with a gas output of 80% o over a wide range of current densities over a long life.
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Neves, Nathalia Costa Viana. "Aplica??o da t?cnica eletroanal?tica de pulso diferencial usando o eletrodo de carbono v?treo modificado com ciste?na para monitorar a degrada??o eletroqu?mica de ?cido ox?lico." Universidade Federal do Rio Grande do Norte, 2013. http://repositorio.ufrn.br:8080/jspui/handle/123456789/17732.
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Previous issue date: 2013-07-31In this paper, the technique of differential pulse voltammetry (DPV) has been studied for monitoring the concentration of oxalic acid (OA) during their electrochemical oxidation (EO) in acidic medium using platinum anode supported on titanium (Ti / Pt). The DPV was standardized and optimized using a glassy carbon electrode modified with cysteine. The modification with cysteine was developed electrochemically, forming a polymeric film on the surface of the glassy carbon electrode. The formation of the polymer film was confirmed by analysis of scanning electron microscope and atomic force microscope, confirming the modification of the electrode. The electrochemical degradation was developed using different current densities 10, 20 30 and 40 mA cm -2 electrode with Ti / Pt observing the degradation of oxalic acid, and monitored using the method of KMnO4 titration. However, the analyzes with DPV showed the same behavior elimination of oxalic acid titration. Compared with the titration method classical observed and DPV could be a good fit, confidence limits of detection and confirming the applicability of the technique electroanalytical for monitoring the degradation of oxalic acid
No presente trabalho, a t?cnica de voltametria de pulso diferencial (DPV) foi estudada para o monitoramento da concentra??o de ?cido ox?lico (OA) durante a sua oxida??o eletroqu?mica (EO) em meio ?cido utilizando o ?nodo de platina suportada em tit?nio (Ti/Pt). A t?cnica de DPV foi padronizada e otimizada usando um eletrodo de carbono v?treo modificado com ciste?na. A modifica??o com ciste?na foi desenvolvida eletroquimicamente, formando um filme polim?rico na superf?cie do eletrodo de carbono v?treo. A forma??o do filme polim?rico foi confirmada por an?lise de Microsc?pio Eletr?nico de Varredura e Microsc?pio de For?a At?mica, confirmando a modifica??o na superf?cie do eletrodo. A degrada??o eletroqu?mica foi desenvolvida usando diferentes densidades de corrente, 10, 20 e 30 mA cm-? com eletrodo de Ti/Pt, observando a degrada??o do ?cido ox?lico, sendo monitorado empregando a metodologia de titula??o com KmnO4. No entanto, as an?lises com DPV mostraram o mesmo comportamento de elimina??o do acido ox?lico, observado com a titula??o. Comparado com o m?todo de titula??o cl?ssica e DPV conseguiu-se um bom ajuste, intervalos de confian?a e limites de detec??o confirmando a aplicabilidade da t?cnica eletroanal?tica para o monitoramento da degrada??o de ?cido ox?lico
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Vaudez, Stéphane. "Frittage des combustibles MOX : influence des conditions d’élaboration et de la pression partielle d’oxygène." Thesis, Bordeaux, 2022. http://www.theses.fr/2022BORD0117.
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Les phénomènes de diffusion se produisant lors du frittage des oxydes mixtes d’uranium et de plutonium (MOX) dépendent du potentiel d’oxygène de l’atmosphère du four. L’atmosphère et la température engendrent des écarts à la stœchiométrie oxygène, appelée rapport O/M, dans l’oxyde mixte U1-yPuyO2±x. Ces travaux de thèse ont porté sur une meilleure connaissance de l’évolution du rapport O/M et de la microstructure des céramiques en fonction de la composition du mélange UO2/PuO2/(UPu)O2 et du potentiel d’oxygène au cours du frittage. Leurs effets sur la densification et les microstructures ont été étudiés, ce qui a permis de proposer la mise œuvre d’une poudre de solution solide (UPu)O2 obtenue par coprécipitation oxalique.Un suivi innovant de la PO2 a été conçu par un asservissement et des mesures entrée / sortie des fours par des pompes oxygène et sondes zircone. Ainsi, le rapport O/M a pu être suivi quantitativement tout au long d’un cycle de frittage. Il permet une bien meilleure compréhension des échanges d’oxygène en température entre l’échantillon et l’atmosphère. Un écart important entre les prévisions des calculs thermodynamiques et les données expérimentales est observé, même après plusieurs heures à 1700°C, écart particulièrement sensible à la formation de la solution solide (UPu)O2 ainsi qu’aux échanges locaux solide/gaz. Un schéma réactionnel de variation du rapport O/M au cours du temps, en faisant volontairement varier la PO2 du gaz a permis d’orienter les cycles de frittage pour obtenir la microstructure et le rapport final O/M souhaités.Ces nouvelles connaissances serviront de données d’entrée pour la modélisation de l’étape de frittage et ainsi de nouveaux cycles de frittage en rupture en four batch ou en four continu sont envisagés. Ils permettent d’obtenir de nouveaux produits et/ou des gains procédés. Ces avantages peuvent être couplés par l’apport bénéfique de la présence de solution solide (UPu)O2 en tant que nouvelle matière premièreDiffusion phenomena occurring during the sintering of mixed uranium and plutonium oxides (MOX) depend on the oxygen potential of the furnace atmosphere. The atmosphere and the temperature generate deviations from the oxygen stoichiometry, called O/M ratio, in the mixed oxide U1-yPuyO2±x. The PhD work focused on a better understanding of the evolution of the O/M ratio and the ceramic microstructure as a function of the composition of the UO2 / PuO2 / (UPu)O2 mixture and of the oxygen potential during sintering. Their effects on densification and microstructures have been studied and have led to proposing the implementation of a (UPu)O2 solid solution powder obtained by oxalic coprecipitation.An innovative monitoring of PO2 has been designed by stabilizing and controlling O2 input/output measurements of the ovens by oxygen pumps and zirconia probes. It allows a much better understanding of the oxygen exchanges in temperatures between the sample and the atmosphere. A significant difference between the thermodynamic calculations and experimental data is observed, even after several hours at 1700°C. The kinetic effects are particularly sensitives to the formation of the (UPu)O2 solid solution as well as to local solid/gas exchanges. A reaction scheme for varying the O/M ratio over time, by voluntarily varying the PO2 of the input gas makes it possible to design sintering cycles in order to obtain the desired microstructure and final O/M ratio.This new knowledge will be used as input data for the modelling of the sintering step. New sintering cycles in batch oven or in continuous oven could then be considered. They make possible to obtain new products and / or process gains. These advantages can be coupled with the beneficial contribution of the presence of a solid solution as a new raw material
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Clark, Tad Dee. "An Analysis of Microstructure and Corrosion Resistance in Underwater Friction Stir Welded 304L Stainless Steel." Diss., BYU ScholarsArchive, 2005. http://contentdm.lib.byu.edu/ETD/image/etd872.pdf.
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