Littérature scientifique sur le sujet « Alkaline reaction environment »
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Articles de revues sur le sujet "Alkaline reaction environment"
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Nikolaychuk, P. A. « Determination of Partial Reaction Orders of the Reduction of Potassium Permanganate by Ethanol in Various Environments ». Herald of the Bauman Moscow State Technical University. Series Natural Sciences, no 3 (108) (juin 2023) : 118–30. http://dx.doi.org/10.18698/1812-3368-2023-3-118-130.
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A spectrophotometric kinetic study of the reaction of the potassium permanganate reduction by excess ethanol in acidic, neutral and alkaline environments was performed. The reaction mixtures were prepared from the solutions of potassium permanganate of different concentrations (0.0004, 0.001 and 0.002 М) and either the solutions of sulphuric acid (1, 3 and 10 %), water, or the solutions of sodium hydroxide (0.01, 0.04 and 0.1 М). The kinetic curves were recorded with the spectrophotometer at the wavelengths of 525 nm (in acidic environment), 400 nm (in neutral environment) and 605 nm (in alkaline environment). The initial reaction rates were determined from the slopes of the initial linear parts of the kinetic curves. Using the differential van’t Hoff method, the partial reaction orders were determined. It was shown that in the acidic environment the partial reaction order with respect to permanganate is close to 1.5, and that with respect to hydrogen ions is close to 0.6. In the neutral and alkaline environments the reaction obeys the first partial order with respect to permanganate, and the partial order of the reaction in alkaline environments with respect to hydroxyl-ions is close to 0.8. It was also shown that the effective rate constants of the reaction in acidic and alkaline environments are significantly higher than that in neutral environment
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Reddy, K. Chiranjeevi, et Kolluru V. L. Subramaniam. « Quantitative phase analysis of slag hydrating in an alkaline environment ». Journal of Applied Crystallography 53, no 2 (13 mars 2020) : 424–34. http://dx.doi.org/10.1107/s1600576720001399.
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An X-ray diffraction (XRD)-based evaluation of the crystalline and amorphous phases in slag hydrating in an alkaline environment is presented. A method is developed for the quantification of the amorphous phases present in hydrating slag in a sodium hydroxide solution. In hydrating slag, the amorphous reaction product is identified as calcium aluminosilicate hydrate. A water-soluble sodium-based amorphous reaction product is also produced. The XRD-based quantification method relies on the direct decomposition of the XRD intensity pattern of the total amorphous phase present in partially hydrated slag into the intensity patterns of the amorphous unreacted slag, the hydrate and the sodium-based product. The unreacted slag content in partially hydrated slag is also determined from the decomposition of the intensity signature of the total amorphous phase. An independent verification of the amorphous unreacted slag content in hydrating slag is obtained from measurements of blends of unhydrated and partially hydrated slag. The XRD-based phase-quantification procedure developed here provides a basis for evaluating the extent of reaction in hydrating slag.
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Tutolo, Benjamin M., Robert Perrin, Rachel Lauer, Shane Bossaer, Nicholas J. Tosca, Alec Hutchings, Serhat Sevgen et al. « Groundwater-Driven Evolution of Prebiotic Alkaline Lake Environments ». Life 14, no 12 (7 décembre 2024) : 1624. https://doi.org/10.3390/life14121624.
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Alkaline lakes are thought to have facilitated prebiotic synthesis reactions on the early Earth because their modern analogs accumulate vital chemical feedstocks such as phosphate through the evaporation of dilute groundwaters. Yet, the conditions required for some building block synthesis reactions are distinct from others, and these conditions are generally incompatible with those permissible for nascent cellular function. However, because current scenarios for prebiotic synthesis have not taken account of the physical processes that drive the chemical evolution of alkaline lakes, the potential for the co-occurrence of both prebiotic synthesis and the origins and early evolution of life in prebiotic alkaline lake environments remains poorly constrained. Here, we investigate the dynamics of active, prebiotically relevant alkaline lakes using near-surface geophysics, aqueous geochemistry, and hydrogeologic modeling. Due to their small size, representative range of chemistry, and contrasting evaporation behavior, the investigated, neighboring Last Chance and Goodenough Lakes in British Columbia, Canada offer a uniquely tractable environment for investigating the dynamics of alkaline lake behavior. The results show that the required, extreme phosphate enrichments in alkaline lake waters demand geomorphologically-driven vulnerability to evaporation, while the resultant contrast between evaporated brines and inflowing groundwaters yields Rayleigh–Taylor instabilities and vigorous surface–subsurface cycling and mixing of lake and groundwaters. These results provide a quantitative basis to reconcile conflicting prebiotic requirements of UV light, salinity, metal concentration, and pH in alkaline lake environments. The complex physical and chemical processing inherent to prebiotic alkaline lake environments thus may have not only facilitated prebiotic reaction networks, but also provided habitable environments for the earliest evolution of life.
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Wei, Shaohua, Hongpeng Zhang, Haiyan Zhu, Lianyuan Wang, Jing Liang et Zhenxing Cheng. « Study on detoxification property of alkaline-modified MoO42--H2O2 decontaminants against PhSMe under subzero environment ». E3S Web of Conferences 267 (2021) : 02061. http://dx.doi.org/10.1051/e3sconf/202126702061.
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The decontaminant activated by MoO42- (MoO42--H2O2) suitable for subzero environment shows strong oxidizing ability and weak nucleophilicity due to its acid. In this paper, in order to improve nucleophilicity and retain oxidation of MoO42--H2O2 as far as possible, NH3 and NaOH were used as alkaline modifiers, and PhSMe was used as a simulant of HD to study the oxidation rate and products of sulfides by alkaline-modified MoO42--H2O2 below zero. Results showed that the reaction rate constants decreased with the increase of pH in both NH3 and NaOH modified MoO42--H2O2 at -20°C, and the relative ratio of sulfone to sulfoxide increased especially at pH>9. The reaction activation energy Ea of PhSMe oxidation in the alkaline-modified MoO42--H2O2 decontaminants was lower than that in the MoO42--H2O2 decontaminant, which indicated that the sensitivity of the oxidation reaction rate to temperature in MoO42--H2O2 was reduced after modification.
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Koyama, M., Y. Amano, S. Liu et T. Ishimoto. « Reaction Mechanism of Ethanol Oxidation over Gold Catalyst under Alkaline Environment ». ECS Transactions 50, no 2 (15 mars 2013) : 1907–12. http://dx.doi.org/10.1149/05002.1907ecst.
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Zhao, Wan, Hongshuai Cao, Liting Ruan, Shaoying He, Zhiai Xu et Wen Zhang. « High-performance self-supporting AgCoPO4/CFP for hydrogen evolution reaction under alkaline conditions ». RSC Advances 12, no 25 (2022) : 15751–58. http://dx.doi.org/10.1039/d2ra02621j.
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Krnel, Kristoffer, Goran Dražič et Tomaž Kosmač. « Degradation of AlN Powder in Aqueous Environments ». Journal of Materials Research 19, no 4 (avril 2004) : 1157–63. http://dx.doi.org/10.1557/jmr.2004.0150.
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The reactivity of AlN powder in an aqueous environment was studied by measuring the pH and the temperature during the hydrolysis of the powder at room and elevated temperatures. The influences of the powder concentration and the starting pH of the slurry were also investigated. The results of the measurements at room temperature show that there is an incubation time before the start of the AlN hydrolysis reactions. Once this incubation time is over, the pH and the temperature of the slurry start to increase, indicating the onset of the reactions. A higher starting temperature not only speeds up the reaction of the AlN powder with water, but it also shortens the incubation time. In addition, the starting temperature influences the morphology of the reaction product: at temperatures below 60 °C, the final product of the hydrolysis is crystalline Al(OH)3, whereas at higher temperatures (above 60 °C), crystalline AlOOH is formed. At very low pH values (pH = 1), the reaction of AlN powder with water is prevented (i.e., the incubation time is very long), whereas in an alkaline environment, the incubation time is approximately the same as in distilled water, but the reaction is accelerated.
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Mendonça Inocêncio, Carlos Victor Mendonça, Claudia Morais et Boniface Kokoh. « Transition Metal Sulfide-Based Electrocatalysts for Hydrogen Evolution Reaction in Alkaline Environment ». ECS Meeting Abstracts MA2021-01, no 47 (30 mai 2021) : 1922. http://dx.doi.org/10.1149/ma2021-01471922mtgabs.
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Fu, Luhong, Shupeng Wang, Junlin Cai, Hongpu Huang, Fulin Yang et Shuifen Xie. « Recent advances in platinum-group-metal based electrocatalysts for alkaline hydrogen oxidation reaction ». Chemical Synthesis 3, no 4 (2023) : 53. http://dx.doi.org/10.20517/cs.2023.53.
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The reaction kinetics of hydrogen oxidation reactions (HOR) unfavorably decreases by 2~3 orders of magnitude under alkaline conditions, even on the most active platinum-group-metal (PGM) electrocatalysts. This sticky problem severely restricts the efficiency and commercialization of anion-exchange membrane fuel cells (AEMFCs). So far, no other material has HOR electrocatalytic performance comparable to PGM-based electrocatalysts. Forced by the scarce reserves and high prices of PGMs, it is significant to elaborately design and synthesize PGM-based electrocatalysts with ultimately atomic utilization and substantially improved alkaline HOR performance. In this review, we summarize recent advances in the structure engineering approaches to synthesis of advanced PGM-based nanocatalysts toward enhanced alkaline HOR performance. The generally acknowledged catalytic mechanisms with corresponding activity descriptors are reviewed firstly to deeply understand the discrepancies in the HOR kinetics of alkaline and acidic reactions. Then, several representative strategies are emphasized and discussed at length by changing the chemical and coordination environment and size/morphology of nanocatalysts. Meanwhile, the influence factors for the performance of AEMFC devices constructed by PGM-based anode catalysts are briefly highlighted. In conclusion, strategies for boosting the electrocatalytic performance and challenges on the roles of catalytic mechanism insights and practical AEMFC applications are finally outlined. We hope this review will guide the design and catalytic mechanism research of novel PGM-based alkaline HOR catalysts, thereby promoting their further development and application in AEMFC technologies.
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An, Lingyun, Chenggong Chang, Fengyun Yan et Jianhong Peng. « Study on the Deterioration Mechanism of Magnesium Oxychloride Cement under an Alkaline Environment ». Materials 16, no 17 (30 août 2023) : 5924. http://dx.doi.org/10.3390/ma16175924.
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The deterioration process and deterioration mechanism of magnesium oxychloride cement (MOC) in an alkaline environment were studied using a scanning electron microscope (SEM), an X-ray diffractometer (XRD), a Fourier transform infrared spectrometer (FT-IR) and a micro-electro-hydraulic servo pressure testing machine to investigate the effects of soaking time in 10 wt.% NaOH solution on the macro- and micro-morphology, phase composition and compressive strength of MOC samples. The results show that the deterioration of MOC samples under an alkaline environment is mainly caused by the alkaline environment providing more OH− ions, which can react with 5Mg(OH)2·MgCl2·8H2O (P 5) in the sample. The resulting reaction gives rise to a faster decomposition of 5Mg(OH)2·MgCl2·8H2O (P 5) and a substantial reduction in the strength of the sample, and finally leads to a gradual deterioration of MOC samples. Meanwhile, immersion time exhibits a significant effect on MOC samples. The extension of immersion time coincides with more OH− ions entering the sample, and the greater presence of OH ions increases the likelihood that more P 5 will produce a hydrolysis reaction, further resulting in the increased deterioration of the sample. After soaking for 6 h in alkaline media, the main phase composition of the surface layer of an MOC sample changes to MgO and Mg(OH)2, and its microscopic morphology is also dominated by round sheets, giving rise to a sharp decrease in its compressive strength (52.2%). When the immersion time is prolonged to 72 h, OH− ions have already immersed into the inner core of the sample, causing the disappearance of P 5 from the whole sample. At the same time, both the surface and inner core of the sample exhibit a disc-shaped morphology, and chalking phenomena also appear on the surface of the sample. This reduces the compressive strength of the sample to 13.5 MPa, only 20% of its compressive strength in water. The compressive strength of the sample after 120 h of immersion is as low as 8.6 MPa, which is lower than that of the sample dipped in water for 21 days (9.5 MPa). As a result, the MOC samples studied in alkaline environments exhibit a faster deterioration rate, mainly because of a faster hydrolysis reaction by P 5, caused by more OH− ions.
Thèses sur le sujet "Alkaline reaction environment"
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Delugeau, Lou. « Étude de l'action d'une bilirubine oxydase sur la lignine Kraft en milieu alcalin : caractérisations et étude de modèles ». Electronic Thesis or Diss., Bordeaux, 2024. http://www.theses.fr/2024BORD0363.
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La lignine est le biopolymère aromatique le plus abondant sur Terre, mais son hétérogénéité et sa faible solubilité dans les solvants usuels en limitent la valorisation. Cependant, de nombreux efforts de recherche se concentrent sur la valorisation enzymatique de la lignine. Dans ce travail, une fraction de lignine Kraft soluble dans l'eau à pH neutre a été obtenue après traitement enzymatique par la bilirubine oxydase (BOD). La BOD est une enzyme oxydase multicuivre active à pH 10, où la lignine Kraft est soluble. Cette fraction soluble obtenue est utilisée par un partenaire du projet pour filer des fibres de carbone. Dans ce projet de thèse, les modifications structurelles induites sur la lignine Kraft Indulin AT, ainsi que sur des modèles de type monomères, oligomères et polymères, ont été analysées. L’effet du tampon borate à pH 10 sur des structures biphényles a été mis en évidence. La capacité de couplage oxydant de la BOD en milieu alcalin a été démontré, menant à la dimérisation des modèles phénoliques et à la polymérisation de la lignine KraftLignin is the most abundant aromatic biopolymer on Earth, but its heterogeneity and poor solubility in common solvents limit its valorization. However, significant research efforts are focused on enzymatic lignin valorization. In this study, a water-soluble fraction of Kraft lignin was obtained after enzymatic treatment with bilirubin oxidase (BOD), a multicopper oxidase active at pH 10, where Kraft lignin is soluble. This fraction is used by a project partner to spin carbon fibers. Structural modifications in Kraft Indulin AT lignin, along with monomeric, oligomeric, and polymeric models, were analyzed, demonstrating oxidative coupling, phenolic dimerization, and lignin polymerization
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Zhang, Yuntao. « Effect of calcium-silicon ratio on the expansion of mortar bars due to alkali-silica reaction ». Scholarly Commons, 2014. https://scholarlycommons.pacific.edu/uop_etds/222.
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In this experiment, mortar bars were prepared with three kinds of industrial solid waste and two kind of aggregates. Positive correlation between expansion induced by ASR and C/S ratio was obtained from the experiment result. Expansion of specimens prepared with standard sand and three cementitious materials increased with curing going on, and had expansion at the 14th day less than 0.1%. Expansion of mortar bars prepared with standard sand and cement increased in a linear way and the expansion at the 14th day was 0.195%. Expansion induced by ASR doesn't exhibit a positive correlation with C/S ratio. Expansion of mortar bars prepared with coarse sand and three cementitious materials at the 14th day had a broad range from 0.087% to 0.161%. In each group, expansion increases with curing going on and in latter ages expansion values of different set tend to spread out. Specimens with the C/S ratio smaller than 1 showed innocuous expansion behavior. Specimens with higher C/S ratios got higher expansion at the 14th day. Clear positive correlation between expansion and C/S was observed in each group. Expansion of mortar bars prepared with coarse sand and cement increased in a linear way and reached 0.5% at the 14th day as a deleterious expansion. Clear positive correlation between expansion and C/S ratio were observed from the experiment result. To characterize the positive correlation between expansion induces by ASR and C/S ratio, an approximate classification could be carried out as follows: C/S less than 1(1.034 from regression formula) as innocuous expansion range, C/S from 1to 2.6 (2.576 from regression formula) as both innocuous and deleterious range, and C/S bigger than 2.6 as deleterious range.
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Creazzo, Fabrizio. « Oxygen evolution reaction at cobalt oxides/water interfaces : heterogeneous electrocatalysis by DFT-MD simulations & ; metadynamics Ab initio molecular dynamics study of an aqueous NaCl solution under an electric field Ionic diffusion and proton transfer in aqueous solutions of alkali metal salts Ionic Diffusion and Proton Transfer in Aqueous Solutions under an Electric Field : State-of-The-Art Ionic diffusion and proton transfer of MgCl2 and CaCl2 aqueous solutions : an ab initio study under electric field DFT-MD of the (110)-Co 3 O 4 cobalt oxide semiconductor in contact with liquid water, preliminary chemical and physical insights into the electrochemical environment Enhanced conductivity of water at the electrified air–water interface : a DFT-MD characterization Ions tune interfacial water structure and modulate hydrophobic interactions at silica surfaces ». Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASE012.
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Dans cette thèse, des simulations DFT-MD couplées à des techniques inno-vantes de métadynamique, sont appliquées pour acquérir une compréhensionglobale des interfaces aqueuses d'oxyde de cobalt Co3O4 et CoO(OH) dansla catalyse de la réaction d'évolution de l'oxygène (OER), et ainsi éventuellement aider à la conception de nouveaux catalyseurs basés sur des matériaux non précieux, un domaine clé de la recherche scientifique et technologique, particulièrement important pour l'économie de l'hydrogène, pour les technologies vertes dans une période de temps avec une demande toujours plus croissanteen énergie verte. Dans cette thèse, nous révélons étape par étape les mécanismes de l'OER sur les électrocatalyseurs aqueux d'oxyde de cobalt Co3O4 etCoO(OH) via de nouvelles techniques de métadynamique.Jusqu'à présent, la littérature n'a jamais pris en compte les modificationsau niveau atomique de la structure des électrodes ainsi que de l'eau interfaciale dans leur modélisation des processus OER. Ce manque de connaissances représente clairement un obstacle important au développement de catalyseurs améliorés, qui pourrait être surmonté en utilisant des méthodes capables de suivre les caractéristiques catalytiques de l'OER à l'échelle atomique. Pour la première fois, nous montrons combien il est important de prendre en considération la présence de l'environnement aqueux dans la caractérisation structurale des surfaces du catalyseur, c'est-à-dire (110)-Co3O4 et (0001)-CoO(OH) dans ce travail. Une caractérisation détaillée des propriétés chimiques et physiques des interfaces aqueuses est fournie (la structure, la dynamique, la spectroscopie, le champ électrique), pour les surfaces (110)-Co3O4 et (0001)-CoO(OH) en contact avec l'eau liquide.Une étude détaillée de l'OER est présentée non seulement du point de vue descatalyseurs, mais aussi en abordant le rôle de l'environnement de l'eau dans leprocessus catalytique, ce qui n'a pas été fait auparavant dans la littérature. En conséquence, l'OER en phase gazeuse et en phase liquide sont étudiés ici auxinterfaces aqueuses (110)-Co3O4 et (0001)-CoO(OH) en adoptant une nouvelleapproche de métadynamique d'échantillonnage amélioré, capable d'identifieret caractériser les mécanismes de réaction chimique et d'intégrer pleinement lerôle des degrés de liberté du solvant, permettant ainsi de dévoiler des réactivités chimiques d'une complexité remarquable. L'énergétique, la cinétique et la thermodynamique derrière l'OER sont donc trouvées à ces surfaces d'oxyde de cobalt à l'interface avec l'eauIn this thesis, DFT-MD simulations, coupled with state-of-the-art metadynamics techniques, are applied to gain a global understanding of Co3O4 and CoO(OH) cobalt oxide aqueous interfaces in catalyzing the oxygen evolution reaction (OER), and hence possibly help in the design of novel catalysts basedon non-precious materials, a current key field of research in science and technology, especially of importance for the hydrogen economy, for green technology in a period of time with an ever more growing demand in green-energy. In this thesis, we step-by-step reveal the OER mechanisms on spinel Co3O4 andCoO(OH) cobalt aqueous electrocatalysts carefully and rationally via novelmetadynamics techniques.Up to now, the literature has never taken into account the atomistic modifications on the electrode structure as well as on the interfacial water into their modeling of OER processes. Such lack of knowledge clearly represents a significant hurdle toward the development of improved catalysts, which couldbe overcome by employing methods able to track the catalytic features of theOER at the atomistic scale. For the first time, we show how important itis to take into consideration the presence of the liquid water environment inthe structural characterization of catalyst surfaces, i.e. for (110)-Co3O4 and(0001)-CoO(OH) in this work. A detailed characterization of chemical andphysical properties of the aqueous interfaces is provided (i.e. structure, dynamics, spectroscopy, electric field), for the (110)-Co3O4 and (0001)-CoO(OH)aqueous surfaces.A study of the OER is presented not only by looking at the catalysts, butalso by addressing the role of the water environment in the catalytic process,not done before in literature. Accordingly, both gas-phase and liquid-phaseOER are here investigated at the (110)-Co3O4 and (0001)-CoO(OH) adoptinga novel enhanced sampling metadynamics approach able to address a widerange of chemical reaction mechanisms and to fully include the role of thesolvent degrees of freedom, allowing to unveil reaction networks of remarkablecomplexity. The energetics, kinetics and thermodynamics behind the OER aretherefore found at these cobalt oxide surfaces
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Jye, Luo I., et 羅一傑. « Study of Environmental Effects on Using Pozzolan to Inhibit Alkali-Aggregate Reaction in Concrete ». Thesis, 1999. http://ndltd.ncl.edu.tw/handle/74774754159073438864.
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碩士國立中央大學
土木工程研究所
87
This study is to evaluate the environmental effects on inhibition of alkali-aggregate reaction (AAR) by using fly ash and slag to replace a portion of cement and lithium hydroxide. Reactive aggregate, cement adjusted to have different alkali content, and replacement of different portion of cement by fly ash and slag were mixed to make 2.5×2.5×28.5cm concrete prisms. After 28 days initial curing, the prisms were cured in five different environments including containers with 100% relative humidity, soaked in 2.1%, 3.5%, and 4.9% NaCl solutions, as well as in 1N NaOH solution at 38℃. Test results showed that the use of non-reactive aggregate was effective to inhibit AAR even in high alkali content concrete. The use of fly ash to replace more than 20% cement and slag to replace more than 50% cement could inhibit AAR expansion in any environments studied. The effectiveness of AAR inhibition was improved with increasing fly ash and slag replacement. In extremely high alkali content concrete, the use of fly ash and slag might not be sufficient to inhibit AAR expansion. If the concrete was not properly treated to inhibit AAR, the amount of expansion was increased with increasing the alkali concentration in the environment. The strategy of using fly ash and slag to inhibit AAR should consider the alkali content both in the concrete and in the environments.
Chapitres de livres sur le sujet "Alkaline reaction environment"
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Bi, Songhu, Zhen Geng, Liming Jin, Mingzhe Xue et Cunman Zhang. « Porous Heterogeneous Sulfide Nickel/Nickel Iron Alloy Catalysts for Oxygen Evolution Reaction of Alkaline Water Electrolysis at High Current Density ». Dans Proceedings of the 10th Hydrogen Technology Convention, Volume 1, 116–21. Singapore : Springer Nature Singapore, 2024. http://dx.doi.org/10.1007/978-981-99-8631-6_13.
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AbstractAlkaline water electrolysis is the important pathway for the green hydrogen production, where oxygen evolution reaction (OER) is the rate-limiting step due to the sluggish reaction kinetics. Transition metal heterogeneous catalyst is the kind of important OER catalyst for alkaline water electrolysis due to its good performance, low price and environmental friendliness. In this work, the porous sulfide nickel@nickel iron alloy catalyst (i.e. NM/NS@Ni3Fe) is prepared by the designed high-temperature vulcanization and multi-step electrodeposition method. The NM/NS@Ni3Fe catalyst exhibits an outstanding OER performance in an alkaline environment, with a low potential of 1.53 V at high current density of 1000 mA cm−2 and a low Tafel slope of 89 mV dec−1. The excellent OER performance is attributed to the unique electronic structure of Ni3S2/Ni3Fe heterogeneous interface and the catalyst layer with porous structure. The results indicate that Ni3S2 provides good electronic conductivity and the low electronegativity S atoms increase the formation of oxygen vacancies, which effectively improves the OER performance. In addition, the hydrophilic and porous structure of the electrode facilitates bubbles release and electrolyte flow at high current density. It provides the guidance for the design of porous heterogeneous OER catalysts with good-performance.
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Provis, John L., Syet Li Yong et Jannie S. J. van Deventer. « Characterising the Reaction of Metakaolin in an Alkaline Environment by XPS, and Time- and Spatially-Resolved FTIR Spectroscopy ». Dans RILEM Bookseries, 299–304. Dordrecht : Springer Netherlands, 2015. http://dx.doi.org/10.1007/978-94-017-9939-3_37.
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Martin, L., P. Thomas, P. De Silva et V. Sirivivatnanon. « Role of Aggregate Reactivity, Binder Composition, and Curing Temperature on the Delayed Ettringite Formation and Associated Durability Loss in Concrete ». Dans Lecture Notes in Civil Engineering, 83–91. Singapore : Springer Nature Singapore, 2023. http://dx.doi.org/10.1007/978-981-99-3330-3_11.
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AbstractThe durability of concrete is critical to its worldwide use as a structural material for buildings and infrastructure, with the lifetime service of concrete greatly affecting its economic, environmental, and social costs. Causes of durability loss in some concrete structures can be attributed to the alkali–silica reaction (ASR) and delayed ettringite formation (DEF). Both are chemical reactions that have the potential to cause expansion and strength loss in affected elements. Significant overlap exists in the factors contributing to ASR and DEF in concrete structures, with widely reported evidence of deleterious DEF frequently occurring in conjunction with mild or moderate ASR. For precast concrete, experiments in mortars have provided limits in the alkali and sulfate content of the binder and maximum curing temperatures used to minimize DEF risk. The role of other constituents in concrete specimens, notably the aggregate, has been overlooked. We investigated the role of reactive aggregates and ASR in the susceptibility of concrete to deleterious DEF.
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Schaaf, W., M. Weisdorfer et R. F. Huettl. « Forest Soil Reaction to Drastic Changes in Sulphur and Alkaline Dust Deposition in Three Scots Pine Ecosystems in Northeast Germany ». Dans Atmospheric Environmental Research, 51–77. Berlin, Heidelberg : Springer Berlin Heidelberg, 1999. http://dx.doi.org/10.1007/978-3-642-58382-7_4.
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Feng, Xiao Xin, et Nai Qian Feng. « Mechanism of Using Mineral Admixtures in Concrete to Suppress Alkali-Silica Reaction ». Dans Environmental Ecology and Technology of Concrete, 111–19. Stafa : Trans Tech Publications Ltd., 2006. http://dx.doi.org/10.4028/0-87849-983-0.111.
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Hao, Ting Yu. « Inspection and Analysis of Prestressed Concrete Girders Deteriorated by Alkali-Silica Reaction ». Dans Environmental Ecology and Technology of Concrete, 131–37. Stafa : Trans Tech Publications Ltd., 2006. http://dx.doi.org/10.4028/0-87849-983-0.131.
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Peña, Rosaura, Lourdes Hurtado, Rubi Romero et Reyna Natividad. « Absorption and reaction of CO2 in capillaries ». Dans CIERMMI Women in Science Engineering and Technology TXV, 51–74. ECORFAN, 2021. http://dx.doi.org/10.35429/h.2021.6.51.74.
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The process of carbon dioxide (CO2) reduction to value-added chemicals is being extensively studied worldwide. The main purpose is to decrease emissions to the environment that are associated with global warming, as well as the creation of renewable and sustainable energy sources. In the aforementioned process, the absorption of CO2 is of paramount importance as well as the reactor where the CO2 conversion takes place. In this context, the objective of this chapter is to present and analyze the results of the CO2 absorption in alkaline solutions in capillary reactors. A hydrodynamic study is included in order to establish the operational window of liquid and gas velocities in order to achieve the Taylor flow regime. All experiments were conducted in a capillary reactor (dc = 3 mm). The studied variables were temperature, NaOH concentration (0-0.75 M) and capillary length (300 and 100 mm). It was found that the volumetric mass transfer coefficient of the absorption of CO2 in water increases when the temperature decreases, while the CO2 absorption in NaOH solutions increases directly with temperature. By means of the Ha number, it was concluded that the mass transfer controlled the absorption process when using alkaline solutions.
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Atkins, Peter. « Fasteners : Acid Catalysis ». Dans Reactions. Oxford University Press, 2011. http://dx.doi.org/10.1093/oso/9780199695126.003.0022.
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I explained the general basis of catalysis in Reaction 11, where I showed that it accelerated a reaction by opening a new, faster route from reactants to products. One of the ways to achieve catalysis in organic chemistry is to carry out a reaction in an acidic or basic (alkaline) environment, and that is what I explore here. In Reaction 27 you will see the enormous importance of processes like this, not just for keeping organic chemists productive but also for keeping us all alive; I give a first glimpse of that later in this section too. Various kinds of acid and base catalysis, sometimes both simultaneously, are going on throughout the cells of our body and ensuring that all the processes of life are maintained; in fact they are the very processes of life. I deal with acid catalysis in this section and base catalysis in the next. The point to remember throughout this section is that an acid is a proton donor (Reaction 2) and a proton is an aggressive, nutty little centre of positive charge. If a proton gets itself attached to a molecule, it can draw electrons towards itself and so expose the nuclei that they formerly surrounded. That is, a proton can cause the appearance of positive charge elsewhere in the molecule where the nuclei shine through the depleted fog of electrons. Because positive charge is attracted to negative charge, one outcome is that a molecule may be converted into a powerful electron-sniffing electrophile (Reaction 16). Another way of looking at the outcome of adding a proton is to note that a C atom with a positive charge is a target for nucleophilic missile attack (Reaction 15). Therefore, if a proton draws the electron cloud away from a nearby atom, then its presence is like a fifth-column agent preparing a target for later attack. Let’s shrink and watch as some acid is added to a molecule that contains a –CO– group, such as acetic acid. The protons provided by the added acid are riding on water molecules, as H3O+ ions, and arrive in the vicinity of the acetic acid molecule.
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Bethke, Craig M. « Evaporation ». Dans Geochemical Reaction Modeling. Oxford University Press, 1996. http://dx.doi.org/10.1093/oso/9780195094756.003.0022.
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The process of evaporation, including transpiration (evaporation from plants), returns to the atmosphere more than half of the water reaching the Earth’s land surface; thus, it plays an important role in controlling the chemistry of surface water and groundwater, especially in relatively arid climates. Geochemists study the evaporation process to understand the evolution of water in desert playas and lakes as well as the origins of evaporite deposits. They also investigate environmental aspects of evaporation (e.g., Appelo and Postma, 1993), such as its effects on the chemistry of rainfall and, in areas where crops are irrigated, the quality of groundwater and runoff. To model the chemical effects of evaporation, we construct a reaction path in which H2O is removed from a solution, thereby progressively concentrating the solutes. We also must account in the model for the exchange of gases such as CO2 and O2 between fluid and atmosphere. In this chapter we construct simulations of this sort, modeling the chemical evolution of water from saline alkaline lakes and the reactions that occur as seawater evaporates to desiccation. We choose as a first example the evaporation of spring water from the Sierra Nevada mountains of California and Nevada, USA, as modeled by Garrels and Mackenzie (1967). Their hand calculation, the first reaction path traced in geochemistry (see Chapter 1), provided the inspiration for Helgeson’s (1968 and later) development of computerized methods for reaction modeling. Garrels and Mackenzie wanted to test whether simple evaporation of groundwater discharging from the mountains, which is the product of the reaction of rainwater and CO2 with igneous rocks, could produce the water compositions found in the saline alkaline lakes of the adjacent California desert. They began with the mean of analyses of perennial springs from the Sierra Nevada (Table 18.1). The springs are Na-Ca-HCO3 waters, rich in dissolved silica.
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Ebrahimi, Eisa, et Mohammad Reza Ojani. « Phosphorus Dynamics in Soil-Water-Sediment Environment ». Dans Phosphorus in Soils and Plants. IntechOpen, 2024. http://dx.doi.org/10.5772/intechopen.113225.
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Phosphorus, a crucial element for plant growth, is relatively scarce in the Earth’s crust. Its availability in surface soils ranges from 100 to 50 mg/kg. Plants can only absorb phosphorus in the form of orthophosphates, with H2PO4- being most absorbable at low pH levels. The average phosphorus concentration in soil solution is about 0.05 mg/L, but plant-satisfying levels range from 0.003 to 0.3 mg/L, underscoring the need for judicious phosphorus fertilization. Storage and stabilization reactions in soil, mainly facilitated by iron and aluminum oxides, play a key role. Compounds in most soils use hydroxyl exchange mechanisms for H2PO4- adsorption. Under alkaline conditions, minerals like calcium carbonate can absorb H2PO4-/ HPO42−, leading to precipitation. To ensure plant health, phosphorus fertilizers, especially calcium orthophosphates like triple superphosphate, are commonly used. These fertilizers offer essential phosphorus for plant growth and development, supporting vital processes like respiration and photosynthesis. Excess phosphorus in aquatic ecosystems, known as eutrophication, poses environmental risks, often originating from concentrated agricultural and livestock operations. Proper management of phosphorus inputs is crucial for balancing plant growth support with environmental preservation. Understanding phosphorus dynamics in soil, water, and sediments is vital for sustainable agriculture and conservation efforts. Adsorption isotherms provide insights into phosphorus absorption mechanisms in sediments, impacting water quality in surface and subsurface systems.
Actes de conférences sur le sujet "Alkaline reaction environment"
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Maheswari, S., P. Sridhar et S. Pitchumani. « Palladium supported on partially unzipped carbon nanotube as a methanol tolerant catalyst for oxygen reduction reaction in alkaline medium ». Dans CARBON MATERIALS 2012 (CCM12) : Carbon Materials for Energy Harvesting, Environment, Nanoscience and Technology. AIP, 2013. http://dx.doi.org/10.1063/1.4810059.
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Dong, Fang, Enguang Zhang, Qiaowei Tang, Qinping Guo et Jinli Qiao. « Doped Mesoporous Carbons Derived from Transition Metal Iron and Chitosan as Efficient Non-Precious Cathode Catalysts for Oxygen Reduction Reaction in Alkaline Electrolyte ». Dans 2017 6th International Conference on Energy, Environment and Sustainable Development (ICEESD 2017). Paris, France : Atlantis Press, 2017. http://dx.doi.org/10.2991/iceesd-17.2017.169.
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Albqmi, Mha, Amani Belaiba et Gassan Hodaifa. « VALORIZATION OF RED MUD AS A CATALYST IN THE TREATMENT OF OLIVE MILL WASTEWATER BY FENTON REACTION ». Dans 22nd SGEM International Multidisciplinary Scientific GeoConference 2022. STEF92 Technology, 2022. http://dx.doi.org/10.5593/sgem2022v/4.2/s18.19.
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The worldwide olive oil sector is a strategic sector for olive oil producing countries due to olive oil nutrition and health benefits. With what is being produced of olive oil, it continues to produce wastewater with a significant environmental impact due to the high organic load and the biochemical composition of this wastewater, particularly, the presence of microbial growth inhibiting compounds such as phenolic compounds, which makes its biological treatment difficult. On other way, red mud, the main leaching residue resulting from the alkaline treatment of bauxite (Bayer process), can be used as catalyst in chemical processing. Bayer red mud reveals high alkalinity, strong water absorption, and a large content of iron. The presence of metals in the composition of the red mud, such as iron dioxide (hematite), titanium dioxide, etc. allows its use as a catalyst in advanced oxidation processes. In this work, red mud has been revalued as a catalyst in the treatment of olive mill wastewater (OMW) by Fenton reaction. All experiments were carried out at laboratory scale in reactor with capacity of 500 cm3. Experiments have been carried out at different concentrations of red mud 0.05, 0.10, 0.5, 1.0, 2.0, 4.0, 5.0, 20, and 30 g/L. In parallel, three control experiments were carried out using only hydrogen peroxide or hydrochloric acid or red mud without pH adjustment (adsorption experiment). Experimental results have determined that the introduction of red mud as a catalyst in the like Fenton reaction (H2O2/red mud) with concentrations higher than 0.05 g/L has allowed the increase of the degradation percentages until reaching stable values at red mud concentrations higher than 5 g/L. The removal percentages at 0.5 g/L of red mud were COD = 47.1 %, total organic carbon (TOC) = 58.1 %, total carbon (TC) = 66.8 %, total nitrogen = 44.1 %, and total phenolic compounds (TPCs) = 63.5 % versus 57.2 % for COD, 74.4 % for TOC, 79.9 % for TC, 70.7 % for TN, and 66.0 % for TPCs in Fenton like reaction with 5 g/L of red mud. The common operating conditions were initial COD of OMW = 6171.9 mg O2/L, initial TOC of OMW = 3253.7 mg/L, pH = 3, magnetic agitation speed = 460 rpm, environment temperature, and the H2O2 at 10 % (w/v) added to the OMW according to the stoichiometry of the reaction. Given these results, it can be concluded that red mud can be a promising catalyst in oxidation systems based on the Fenton reaction allowing the incorporation of wastes into new green processes leading to the achievement of circular economy in industrial processes.
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Moschetti, Ilaria, Lola Sarrasin, Guillaume Blain, Eros Mossini, Mario Mariani et Abdesselam Abdelouas. « Effect of Curing Time and Water to Binder Ratio on Magnesium Potassium Phosphate Cement Exposed to Gamma Irradiation ». Dans ASME 2023 International Conference on Environmental Remediation and Radioactive Waste Management. American Society of Mechanical Engineers, 2023. http://dx.doi.org/10.1115/icem2023-109457.
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Abstract Metallic Waste (MW) is one type of low and intermediate radioactive waste. It is estimated that the current fleet of civil nuclear power reactors throughout the world would produce about 500 000 tons of this kind of waste in the near future due to their advancing age. MW comes mainly from spent fuel reprocessing facility, storage ponds and reactor primary circuit systems. MW typically consists of stainless steels or nickel alloys, which are the primary components of nuclear installations. Aluminum and beryllium belong to this waste category and are also called Reactive Metallic Waste (RMW). The major risk involved in trying to encapsulate RMW is corrosion, resulting in hydrogen release. In a specific pH range, MW forms a stable protective oxide coating. It is therefore important to employ matrices that provide a favorable environment, reducing the reactivity of MW and thus the production of hydrogen gas. Ordinary Portland Cement (OPC) is not recommended for RMW encapsulation due to its extremely alkaline pore solution which favors corrosion. Moreover, the high content of free water may further contribute to H2 production due to water radiolysis. One of the potential matrices being considered for the encapsulation of RMW is Magnesium Potassium Phosphate Cement (MKPC), produced from the acid-base reaction between magnesium oxide (MgO) and dihydrogen potassium phosphate salt (KH2PO4). The lower pH ensures RMW remains inside the passivation range, while maintaining high performance characteristics, such as compressive strength and stability towards leaching. To assess the applicability of MKPC as a containment matrix for radioactive RMW, it is important to evaluate its resistance to radiation, thus ascertaining the radiolytic production of H2, as well as its durability. In this study, a Cs-137 gamma source has been used to irradiate: i. at 200 kGy samples with different curing ages, ranging from few days to 28 days, to shed light on the effects of irradiation during the curing period, ii. at different doses samples with the same 28 days curing time (reference) to better understand the effect of the total absorbed dose, iii. at 200 kGy samples with slightly different water to binder ratio to investigate the impact on radiolytic production of H2. To evaluate possible radiation-induced modification of the structure and morphology of the MKPC, XRD and SEM-EDX have been used. Micro-gas chromatography analyses have been performed to determine the amount of radiolytic H2 released. The water immersion resistance of irradiated MKPC is also evaluated by a standard leaching protocol. Non irradiated MKPC samples have been tested as reference. The encouraging results obtained in this work further promote the use of MKPC for the encapsulation of RMW.
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Chida, Tsutomu, Aritomo Yamaguchi, Atsushi Takahashi, Kousuke Hiromori, Naoki Mimura et Naomi Shibasaki-Kitakawa. « Process design for efficient production from glycerol into high-value chemicals ». Dans 2022 AOCS Annual Meeting & Expo. American Oil Chemists' Society (AOCS), 2022. http://dx.doi.org/10.21748/wimj4199.
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There is an urgent need to develop effective methods to use glycerol, a by-product of biodiesel production, by converting it into high-value chemicals. The by-product glycerol is contaminated with strong alkaline as a catalyst, and the environmental loads of the purification process to remove the contaminants has been a bottleneck to its utilization. As one way to solve this problem, it has been reported that glycerol can be converted to glyceric acid (GA), which is used as a pharmaceutical raw material, by partial oxidation of glycerol using an Au catalyst under alkaline condition. However, the GA yield is low because many side reactions proceed simultaneously. To construct a practical process for efficient GA production, it is necessary to both experimentally analyze the reaction mechanism and to develop a kinetic model that can quantitatively predict the reaction behavior under a wide range of conditions.The purpose of this study is to establish a methodology for process design of efficient production of GA from the by-product glycerol. In our previous study, the reaction mechanism including alkaline and the reactive oxygen species OOH, which is formed from O2 and H2O on Au catalyst, in GA formation was clarified and a kinetic model taken it into account was constructed. In present study, the model was additionally taken temperature dependency into account and enabled to predict GA yield in wide range of operating conditions. In order to design the catalysts, the relationship between GA yield and coverages of adsorbed species on active sites was investigated by the model simulation and it was revealed that the affinity between support and H2O greatly affects GA yield, suggesting that the support, which has strong interaction with H2O, increases the GA yield.
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MALINAUSKAITĖ, Regina, et Edvardas KAZLAUSKAS. « INVESTIGATION OF SOW LENTIL REACTION TO IONIZED ALKALINE WATER DURING EARLY STAGES OF ONTOGENESIS ». Dans Rural Development 2015. Aleksandras Stulginskis University, 2015. http://dx.doi.org/10.15544/rd.2015.020.
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Plant physiological processes related to plant growth and development strongly depends on the environmental stress factors. Response to stress appears as a complex of different reactions with a particular feedback on plants. Influence of ionized alkaline water to sow lentil physiological reactions was investigated by analyzing changes in biomass accumulation, assimilates partitioning and pigment content. Ionized alkaline water at (8.4 pH) was applied during 6–7 and 8–9 leaves development stage. According to experiment results, at the latest stage of investigation, ionized alkaline water increased lens dry matter content more than 1.44 times. During experimental time increase in dry matter content was 13.96 %, when control plants gained only 3.47 %. Ionized alkaline water application resulted in 8.58 % significantly higher root dry matter content compare to control variant. Results of our experiment revealed the significant effect of ionized alkaline water to chlorophyll content. Chlorophyll a and chlorophyll b in control plants had a tendency to decline, whereas in experimental variant with ionized water, increase in pigment concentration was observed.
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Amamoto, Ippei, Hirohide Kofuji, Munetaka Myochin, Tatsuya Tsuzuki, Yasushi Takasaki, Tetsuji Yano et Takayuki Terai. « Separation of Lanthanoid Phosphates From the Spent Electrolyte of Pyroprocessing ». Dans ASME 2009 12th International Conference on Environmental Remediation and Radioactive Waste Management. ASMEDC, 2009. http://dx.doi.org/10.1115/icem2009-16265.
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This study is carried out to make the pyroprocessing hold a competitive advantage from the viewpoint of environmental load reduction and economical improvement. As one of the measures is to reduce the volume of the high-level radioactive waste, the phosphate conversion method is applied for removal of fission products from the melt as spent electrolyte in this paper. Though the removing target elements in the medium are alkali metals, alkaline earth metals and lanthanoid elements, only lanthanoid elements and lithium form the insoluble phosphates by reaction with Li3PO4 or K3PO4. Therefore, as the first step, the precipitation experiment was carried out to observe the behaviours of elements which form the insoluble precipitates as double salts other than simple salts. Then the filtration was experimented to remove lanthanoid precipitates in the spent electrolyte using Fe2O3-P2O5 glass system as a filtlation medium which is compatible material with the glassification. The result of separation of lanthanoid precipitates by filtration was effective and attained almost 100%.
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Gyde, Hartmut, Schmidt-Döhl Frank et Püstow Anna. « Reaction Kinetic Studies of the Electrical Conductivity in Dissolution Experiments for the Identification of Alkali-Reactive Aggregate ». Dans The 8th World Congress on Civil, Structural, and Environmental Engineering. Avestia Publishing, 2023. http://dx.doi.org/10.11159/icsect23.147.
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Sneha, S. S., et K. P. Ramaswamy. « A Comprehensive Review on the Mechanism of Concrete Deterioration in Accelerated Aggressive Environment ». Dans International Web Conference in Civil Engineering for a Sustainable Planet. AIJR Publisher, 2021. http://dx.doi.org/10.21467/proceedings.112.40.
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Concrete is being extensively utilized for the constructional and other allied works on account of its versatility and mechanical properties. However, it exists to be in a state of disequilibrium with its ambient environment owing to its universal alkaline nature and hence is susceptible to deterioration when exposed to aggressive environments. The reactive species emanating from chemical plants, fertiliser industries, marine water, agro-food industries etc., produce detrimental effects on the concrete structures through the dissolution of calcium bearing phases from the hydrated matrix. This degradation culminates in decalcification, volumetric expansion, salt crystallisation, micro-cracking, surface scaling, delamination, spalling and corrosion. Diffusivity, capillary porosity, permeability, chemical nature of hydrated matrix and pore network are the parameters that influence the chemical mechanism of concrete degradation. The mechanism of concrete degradation is distinct for various aggressive species and its fair comprehension remains as one of the challenges in accomplishing the durability based concrete design. This paper critically reviews the basic mechanism of the concrete deterioration in accelerated aggressive environment of mineral acids, organic acids and inorganic salts. In addition to this, a glimpse of the effect of degradation on different binder systems viz., Ordinary Portland Cement system, blended cement system, special cement system and alkali activated system is provided.
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Cho, Yung-Zun, In-Tae Kim, Hee-Chul Yang, Hee-Chul Eun, Hwan-Seo Park et Eung-Ho Kim. « Removal of Alkaline-Earth Elements by a Carbonate Precipitation in a Chloride Molten Salt ». Dans The 11th International Conference on Environmental Remediation and Radioactive Waste Management. ASMEDC, 2007. http://dx.doi.org/10.1115/icem2007-7288.
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Separation of some alkaline-earth chlorides (Sr, Ba) was investigated by using carbonate injection method in LiCl-KCl eutectic and LiCl molten salts. The effects of the injected molar ratio of carbonate ([K2 (or Li2)CO3/Sr (or Ba)Cl2]) and the temperature (450–750 °C) on the conversion ratio of the Sr or Ba carbonate were determined. In addition, the form of the Sr and Ba carbonate resulting from the carbonation reaction with carbonates was identified via XRD and SEM-EDS analysis. In these experiments, the carbonate injection method can remove Sr and Ba chlorides effectively over 99% in both LiCl-KCl eutectic and LiCl molten salt conditions. When Sr and Ba were co-presented in the eutectic molten salt, they were carbonated in a form of Ba0.5Sr0.3CO3. And when Sr was present in LiCl molten salt, it was carbonated in the form of SrCO3. Carbonation ratio increased with a decreasing temperature and it was more favorable in the case of a K2CO3 injection than that of Li2CO3. Based on this experiment, it is postulated that carbonate precipitation method has the potential for removing alkali-earth chlorides from LiCl-KCl eutectic and LiCl molten salts.
Rapports d'organisations sur le sujet "Alkaline reaction environment"
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Desbarats, A. J., et J. B. Percival. Hydrogeochemistry of mine tailings from a carbonatite-hosted Nb-REE deposit, Oka, Quebec, Canada. Natural Resources Canada/CMSS/Information Management, 2023. http://dx.doi.org/10.4095/331256.
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Environmental impacts associated with the mining of carbonatite deposits are an emerging concern due to the demand for critical metals. This study investigates the chemistry of tailings seepage at the former Saint Lawrence Columbium mine near Oka, Québec, Canada, which produced pyrochlore concentrate and ferroniobium from a carbonatite-hosted Nb-REE deposit. Its objectives are to characterize the mineralogy of the tailings and their pore water and effluent chemistries. Geochemical mass balance modeling, constrained by aqueous speciation modeling and mineralogy, is then used to identify reactions controlling the chemical evolution of pore water along its flow path through the tailings impoundment. The tailings are composed mainly of REE-enriched calcite (82 wt. %), biotite (12 wt. %) and fluorapatite (4 wt. %). Minor minerals include chlorite, pyrite, sphalerite, molybdenite and unrecovered pyrochlore. Secondary minerals include gypsum, barite and strontianite. Within the unsaturated zone, pore water chemistry is controlled by sulfide oxidation and calcite dissolution with acid neutralization. With increasing depth below the water table, pore water composition reflects gypsum dissolution followed by sulfate reduction and FeS precipitation driven by the oxidation of organic carbon in the tailings. Concomitantly, incongruent dissolution of biotite and chlorite releases K, Mg, Fe, Mn, Ba and F, forming kaolinite and Ca-smectite. Cation exchange reactions further remove Ca from solution, increasing concentrations of Na and K. Fluoride concentrations reach 23 mg/L and 8 mg/L in tailings pore water and effluent, respectively. At a pH of 8.3, Mo is highly mobile and reaches an average concentration of 83 µg/L in tailings effluent. Although U also forms mobile complexes, concentrations do not exceed 16 µg/L due to the low solubility of its pyrochlore host. Adsorption and the low solubility of pyrochlore limit concentrations of Nb to less than 49 µg/L. Cerium, from calcite dissolution, is strongly adsorbed although it reaches concentrations (unfiltered) in excess of 1 mg/L and 100 µg/L in pore water and effluent, respectively. Mine tailings from carbonatite deposits are enriched in a variety of incompatible elements with mineral hosts of varying reactivity. Some of these elements, such as F and Mo, may represent contaminants of concern because of their mobility in alkaline tailings waters.
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Prusky, Dov, Lisa Vaillancourt et Robert Fluhr. Host Ammonification by Postharvest Pathogens and its Contribution to Fungal Colonization and Symptom Development. United States Department of Agriculture, décembre 2006. http://dx.doi.org/10.32747/2006.7592640.bard.
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Postharvest decay of fruits and vegetables caused by pathogenic and saprophytic fungi significantly impairs the quality and quantity of fresh produce brought to market. Consequently, there is considerable interest in identifying factors that determine the susceptibility of these commodities to pathogen infection. Insidious postharvest decays remain quiescent during fruit growth and harvest, but activate during the postharvest period. A key response to the physiological changes occurring during fruit ripening is the initiation of ammonium secretion by the pathogen. Ammonium ions at the infection site (ammonification) have subsequent effects on both the pathogen and the host. An accompanying alkalinization process resulting from ammonia accumulation contributes to pathogenicity, since some important fungal virulence factors, (such as pectate lyase in Colletotrichum sp.), are significantly expressed only under alkaline conditions. In this proposal, investigated the mechanisms by which ammonification and alkalinization of infected tissues by the pathogen affect the host’s defense response to fungal attack, and instead increase compatibility during postharvest pathogen-host interactions. Our hypotheses were:1) that host signals, including ripening-related changes, induce secretion of ammonia by the pathogen; 2) that ammonia accumulation, and the resultant environmental alkalinization regulate the expression of fungal virulence genes that are essential for postharvest rot development; 3) that ammonification enhanced fungal colonization, by “suppression of host responses”, including production of reactive oxygen species, activation of superoxide, and polyphenol oxidase production. Our objectives were: to analyze: 1) factor(s) which activate the production and secretion of ammonia by the fungus; 2) fungal gene(s) that play role(s) in the ammonification process; 3) the relationship between ammonification and the activation of host defense response(s) during pathogen colonization; and 4) analyze hostgene expression in alkalinized regions of fruits attacked by hemibiotrophic fungi.