Zeitschriftenartikel: „Chromium Oxidation“

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Ledoux, Xiaver, Michel Vilasi, Stéphane Mathieu, Pierre Jean Pantiex, Pascal Del-Gallo und Marc Wanger. „Development of Chromium and Aluminum Coatings on Superalloys by Pack-Cementation Technique“. Advanced Materials Research 278 (Juli 2011): 491–96. http://dx.doi.org/10.4028/www.scientific.net/amr.278.491.

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Austenitic nickel-iron-chromium based superalloys are materials of choice for high temperature applications as they provide high temperature creep resistance associated with a suitable oxidation behavior in the temperature range of 600-1100°C. However, these properties are not sufficient for applications as Steam Methane Reformer (SMR). As a consequence, aluminum and chromium coatings are developed by the pack-cementation technique to improve their corrosion resistance. The oxidation behavior of the coated samples has been carried out in air at 1050°C. Chromium deposition leads to a layer of bcc chromium-iron solid solution. Oxidation tests indicated that a too high chromium concentration induces a too rapid growth of the chromia layer. In the case of aluminum coatings, a layer of -NiAl is formed at the surface of the alloy. It permits a significant decrease of the oxidation rate.

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Dulińska, D., W. Pawlak und Z. Grzesik. „The Prospects In Designing New Generation Of High Temperature Coatings In Automobile Engines“. Archives of Metallurgy and Materials 60, Nr. 2 (01.06.2015): 903–7. http://dx.doi.org/10.1515/amm-2015-0227.

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AbstractThe influence of the chromium layer with the thickness of 1 micrometer sputter-deposited on the X33CrNiMn23-8 and X50CrMnNiNbN21-9 steel surfaces on the oxidation behavior of these steels has been studied at 1173 K in air, using the microthermogravimetric technique. It has been found that coated materials show very good oxidation resistance under isothermal conditions, comparable with that of chromia formers, due to the formation of Cr2O3scales on their surfaces. It has been also demonstrated that the positive effect of chromium addition on the oxidation resistance of investigated steels is observed during a much longer period of time than the life-time of the chromium coating.

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Galerie, Alain, Jean Pierre Petit, Yves Wouters, Julie Mougin, Anusara Srisrual und Peggy Y. Hou. „Water Vapour Effects on the Oxidation of Chromia-Forming Alloys“. Materials Science Forum 696 (September 2011): 200–205. http://dx.doi.org/10.4028/www.scientific.net/msf.696.200.

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The electronic properties of chromia scales grown between 800°C and 900°C on chromium metal and chromia-forming ferritic stainless steels were determined using room temperature PhotoElectroChemistry (PEC) experiments and the relative importance of the n- and p-character of the scales could be assessed. According to the thermodynamic previsions of defects structures, the external part of all the scales grown in oxygen exhibits band gap energy around 3.5 eV, with a marked p-type character on chromium and a possibly n-type behaviour on stainless steels. On the contrary, the internal part of the scales is always n-type, with predominant interstitial chromium defects. A major change appears when chromium or stainless steels are oxidised in water vapour-argon mixtures, where the absence of a p‑type semiconductor in the scales could be evidenced. Hydrogen defects are thought to be responsible of this particular behaviour which leads to a strong reduction of residual stresses due to increased high temperature relaxation. Moreover, the inversion of the growth direction resulting from high mobility of the OH defects makes the chromia scales grown in water vapour more adherent than when grown in oxygen.

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Berthod, Patrice, und Lionel Aranda. „Determination of Diffusion Coefficients Using Thermogravimetric Measurements during High Temperature Oxidation“. Defect and Diffusion Forum 323-325 (April 2012): 289–94. http://dx.doi.org/10.4028/www.scientific.net/ddf.323-325.289.

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Thermogravimetry measurements associated to concentration profiles allow determining a diffusion coefficient at high temperature of the most oxidable one among the metallic elements belonging to the chemical composition of an alloy. In this work the employed method is described and applied to chromia-forming alloys essentially based on nickel but also to selected cobalt-based and iron-based alloys. More precisely DCrvalues were estimated for chromium diffusing through the carbide-free zones developed during high temperature oxidation. The effects of the base element, of the chromium carbides density and of the dendritic orientations on the chromium diffusion were evidenced.

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Ozdilek, Zehra. „Teaching the properties of chromium's oxidation states with a case study method“. Chemistry Education Research and Practice 16, Nr. 1 (2015): 39–52. http://dx.doi.org/10.1039/c4rp00176a.

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The purpose of this study was to investigate how a mixed-method case study affects pre-service science teachers' awareness of hexavalent chromium pollution and content knowledge about the properties of chromium's different oxidation states. The study was conducted in Turkey with 55 sophomores during the fall semester of 2013–2014. The students were taught using a case study about chromium's properties, the qualitative and quantitative analysis methods used with chromium compounds, the effects of chromium compounds on human health, and the chemical techniques that can be used to remove hexavalent chromium from wastewater. Open-ended questions were applied to determine the students' pre- and post-knowledge before and after instruction. An open-ended questionnaire and semi-structured interviews showed that the case study had a positive effect on all participants in terms of increasing their awareness of the hazardous effects of hexavalent chromium. Pair sample and independent samplet-test results revealed that the presenting and the audience groups significantly increased their content knowledge after instruction. On the other hand, while there was no statistically significant difference between the groups on verbal questions, there was a difference between the presenting and the audience groups on calculative questions. This finding shows that the mixed-method case instruction might not have affected all subjects in the same way.

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Escudero-Castejon, Lidia, Sergio Sanchez-Segado, Stephen Parirenyatwa und Animesh Jha. „Formation of Chromium-Containing Molten Salt Phase during Roasting of Chromite Ore with Sodium and Potassium Hydroxides“. Journal for Manufacturing Science and Production 16, Nr. 4 (01.12.2016): 215–25. http://dx.doi.org/10.1515/jmsp-2016-0023.

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AbstractChromium has a wide range of applications including metals and alloys manufacturing, pigments, corrosion resistance coatings and leather tanning. The production of chromium chemicals is based on the oxidative alkali roasting of chromite ores, which leads to the formation of water-soluble alkali chromates. Previous investigations reported that when chromite is roasted with soda-ash, a molten salt containing chromium, which is mainly composed of sodium carbonate and sodium chromate (Na2CO3-Na2CrO4 binary mixture), forms under typical roasting conditions. The physical properties of the liquid phase, which are dependent on the temperature, charge and gangue compositions, play an important role on the oxidation reaction and may limit the chromate recovery by hindering the oxygen transport to the reaction interface. This investigation focuses on the alkali roasting of chromite ore at 1,000 oC using NaOH and KOH, followed by water leaching. The influence of the alkali ratio on the chromium extraction yield is analysed, and the results obtained with both hydroxides are compared. Sample characterisation and thermodynamic analysis, including phase diagrams, equilibrium calculations and computation of liquidus curves, are combined with the purpose of studying the formation of the molten salt phase under different roasting conditions and its effect on the final chromium recovery.

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Oze, Christopher, Norman H. Sleep, Robert G. Coleman und Scott Fendorf. „Anoxic oxidation of chromium“. Geology 44, Nr. 7 (01.06.2016): 543–46. http://dx.doi.org/10.1130/g37844.1.

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Clark, Jeremy N., Douglas R. Glasson und S. Amarasiri A. Jayaweera. „Oxidation of chromium carbide“. Thermochimica Acta 103, Nr. 1 (Juli 1986): 193–99. http://dx.doi.org/10.1016/0040-6031(86)80032-6.

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Chandra-ambhorn, Somrerk, Shigenari Hayashi, Laurence Latu-Romain und Patthranit Wongpromrat. „CHAPTER 4 High Temperature Oxidation of Stainless Steels“. Solid State Phenomena 300 (Februar 2020): 81–106. http://dx.doi.org/10.4028/www.scientific.net/ssp.300.81.

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This chapter is dedicated to the description of high temperature oxidation of both chromia and alumina forming alloys. The defect structures of iron and chromium are firstly reviewed. The effects of elements on stainless steel oxidation behaviour are further addressed. For the chromia-forming stainless steel, the oxidation rate is reduced with the increased silicon content but not in a monotonic manner. Titanium and niobium can reduce breakaway oxidation of Fe–18Cr–10Ni austenitic stainless steel. Titanium can enhance the adhesion of scale to the Fe–18Cr by mechanical keying effect of TiO2 formed at the steel/scale interface. For the alumina-forming stainless steel, the formation of alumina and its transformation during oxidation are reviewed. Chromium can be added to reduce the critical aluminium content in the steels in order to form alumina at high temperatures. The addition of reactive elements with appropriate level can improve scale adhesion and reduce the steel oxidation rate. Refractory element like molybdenum can increase strength of material but also accelerate the oxidation rate of the steels containing reactive elements. The development of new alumina-forming austenitic alloy grades is finally described.

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Dworzański, Wojciech, Ewelina Cholewińska, Bartosz Fotschki, Jerzy Juśkiewicz, Piotr Listos und Katarzyna Ognik. „Assessment of DNA Methylation and Oxidative Changes in the Heart and Brain of Rats Receiving a High-Fat Diet Supplemented with Various Forms of Chromium“. Animals 10, Nr. 9 (21.08.2020): 1470. http://dx.doi.org/10.3390/ani10091470.

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The aim of the study was to determine how feeding rats a high-fat diet supplemented with various forms of chromium affects DNA methylation and oxidation reactions as well as the histology of heart and brain tissue. The rats received standard diet or high-fat diet and chromium at 0.3 mg/kg body weight (BW) in form of chromium (III) picolinate, chromium (III)-methionine, or nano-sized chromium. The content of malondialdehyde (MDA), protein carbonyl (PC), and 8-hydroxydeoxyguanosine (8-OHDG), the level of global DNA methylation and the activity of selected DNA repair enzymes were determined in the blood. In the brain and heart, the content of MDA, PC, 8-OHDG, and levels of global DNA methylation were determined. The brain was subjected to histological examination. The use of a high-fat diet was found to intensify epigenetic changes and oxidation reactions in the heart and brain. It was concluded that epigenetic changes and oxidation of lipids, proteins, and DNA in the heart and brain of rats resulting from the use of a high-fat diet cannot be limited by supplementing the diet with chromium. It was established that the use of chromium to supplement a high-fat diet intensifies the negative epigenetic and oxidative changes in the heart and brain, especially in the case of chromium nanoparticles.

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Berthod, Patrice, Pierric Lemoine und Lionel Aranda. „Study of the Behavior in Oxidation at High Temperature of Ni, Co and Fe-Base Alloys Containing Very High Fractions of Carbides“. Materials Science Forum 595-598 (September 2008): 871–80. http://dx.doi.org/10.4028/www.scientific.net/msf.595-598.871.

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Nine cast alloys reinforced by very high fractions of carbides, Ni-30Cr-xC, Co-30Cr-xC and Fe-30Cr-xC with x varying from 1.2 to 2.0, were tested in oxidation at high temperature between 1,000 and 1,200°C in air for 50 hours. After oxidation, their surfaces and sub-surfaces were characterized. Even for very high carbon contents, the chromia-forming behaviour of the nickel alloys is kept. The oxidation modes of the cobalt alloys and iron alloys are not changed compared to low carbon alloys of these families. The differences of diffusion easiness of chromium in matrix, between nickel alloys, cobalt alloys and iron alloys are the same as for alloys with lower carbon contents, as suggested by the lower chromium gradients in the nickel alloys compared to the two other alloy types. Sub-surface microstructure transformations due to oxidation were observed in some cases (coarsening of carbides due to an inwards diffusion of carbon, change of the sharing between BCC-FCC of iron matrix due to outwards diffusion of chromium). Catastrophic oxidation never occurred for these alloys during the 50 hours of exposition to air at high temperature.

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Şen, Şaduman, Ozkan Ozdemir, A. Sukran Demirkıran und Uğur Şen. „Oxidation Kinetics of Chromium Carbide Coating Produced on AISI 1040 Steel by Thermo-Reactive Deposition Method during High Temperature in Air“. Advanced Materials Research 445 (Januar 2012): 649–54. http://dx.doi.org/10.4028/www.scientific.net/amr.445.649.

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Oxidation of chromium carbide coating formed on AISI 1040 steel deposited by thermo-reactive deposition method (TRD) has been realized by two stepped reactions. In the initial part of the reactions in the oxidation process, carbon atoms combined with chromium on the outer part of the coating layer react with the oxygen in air, effectively up to 120 min. After that, the chromium atoms react with oxygen in the air and produce Cr2O3phase on the coating layer. The higher the temperature and the longer the treatment time, the more the Cr2O3phases became. The kinetic study was realized for the reactions of carbon and chromium with oxygen, individually. The kinetic study of oxidation was calculated by weight changing of the coated samples at the temperatures of 973 K, 1073 K and 1273 K up to 720 min. We established that the chromium carbide coated steel are characterized by an insignificant increase in the mass in the oxidation period up to 3.5 h, after which the degree of oxidation increases somewhat. The nature of oxidation kinetics for chromium carbide coated steel varies from some mass degrease in the initial period ( 2 h) in connection with the formation of CO and CO2to later mass increase with in connection with the formation of Cr2O3layer. The oxidation resistance of chromium carbide coated steel decrease with an increase in oxidation temperature. The growth rate constant of oxidation of chromium carbide coated steel ranged from 5.13x10-13to-9.617x10-11g4.cm-2s-1in the initial period of oxidation (up to 120 min), while it ranged from 3,163x10-13to 2.188 x10-10g4.cm-2s-1in the second period of oxidation test (over 120 min). The activation energies of oxidation of the chromium carbide coated steel are 185 kJ/mol for the initial period and 215 kJ/mol for the second period.

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Schmidt, Diana, und Michael Schütze. „Improved Corrosion Resistance of Superheater Materials in H₂O Containing Environments Using Mn-Diffusion Coatings“. Materials Science Forum 696 (September 2011): 330–35. http://dx.doi.org/10.4028/www.scientific.net/msf.696.330.

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The oxidation resistance of ferritic-martensitic 9% chromium steels in water vapour containing atmospheres is not yet satisfactory. The chromia layer provides little protection because water vapour in the atmosphere is known to promote the formation of the volatile chromium species CrO2(OH)2. If a chromium manganese spinel is formed instead, the vapour pressure of the oxy-hydroxide is greatly reduced and evaporation can largely be avoided. Enrichment of the substrate with manganese was achieved using three different processes: using (i) a sputtering technique, (ii) electrochemical deposition both followed by a diffusion heat treatment, (iii) the pack cementation method. Uniform diffusion of manganese was obtained with all of the investigated processes. The improved oxidation behaviour of the coated samples in synthetic air with 10% water vapour at 650°C was demonstrated.

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Royer, Laurent, Stéphane Mathieu, Christophe Liebaut und Pierre Steinmetz. „Study of the Microstructure and Oxidation Behavior of Chromium Base Alloys Strengthened by NiAl Precipitates“. Materials Science Forum 595-598 (September 2008): 117–25. http://dx.doi.org/10.4028/www.scientific.net/msf.595-598.117.

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In this study, chromium based alloys containing a hardening NiAl phase are investigated from 1100°C to 1300°C in air. The influence of the NiAl content and of the Al/Ni ratio on microstructure modification and on oxidation behaviour are characterized by metallography and thermogravimetry. Increasing the Al/Ni ratio leads to a higher Al content in the chromium solid solution but does not modify the amount of primary NiAl. At high temperature, and for NiAl content exceeding 16 at%, a duplex oxide layer forms at the surface of the alloys exposed in air, alumina in the inner part, and chromia in the outer part. The oxidation behavior is discussed according to oxidation profile and to the thermodynamic predominance diagram of the involved species.

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Uchuskin, Maxim, Igor Trushkov und Anton Makarov. „Furan Oxidation Reactions in the Total Synthesis of Natural Products“. Synthesis 50, Nr. 16 (16.07.2018): 3059–86. http://dx.doi.org/10.1055/s-0037-1610021.

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Recent developments on the transformations of furans under oxidative conditions toward the total synthesis of complex natural compounds are discussed. Reactions and methods are classified according to the type of oxidant used. Comparisons are then made between all the strategies to provide a comprehensive overview. This review covers the most prominent work published from 2011 until 2017.1 Introduction2 Reagents and Methods for Oxidation of the Furan Ring2.1 Singlet Oxygen2.2 Peroxides and Hydroperoxides2.3 Quinones2.4 Halogen-Based Oxidants2.5 Chromium-Based Oxidants3 The Achmatowicz Reaction3.1 Halogen-Based Oxidants3.2 Hydroperoxides3.3 Enzymatic Oxidation4 Conclusion

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Pokhrel, Ganga Raj, und Galaxy Pokhre. „Effect of Chromium on Human-Health: A Review“. BMC Journal of Scientific Research 5, Nr. 1 (31.12.2022): 27–35. http://dx.doi.org/10.3126/bmcjsr.v5i1.50669.

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This review presents the health effects of chromium on the living organism based on previous studies. Chromium (Cr) belongs to the d-block element in the modern periodic table. Chromium has a wide range of oxidation states ranging from -2 to +6. Chromium mostly exists in the environment as trivalent (Cr3+) and hexavalent (Cr6+) states. Both trivalent and hexavalent states of chromiums are derived from the industrial effluents. Ingestion, dermal contact, and inhalation are the most common routes through which chromium enters the human body. Ion chromatography inductively coupled plasmamass spectrometry (IC-ICP-MS) is mostly used for the speciation analysis of metals. Hexavalent chromium is highly soluble and mobile in alkaline and slightly acidic soils, whereas trivalent chromium is less soluble, adheres to the coarse material on the soil, and precipitates as Cr(III) hydroxide. Hexavalent chromium is more detrimental as compared to trivalent chromium. The detrimental effects of chromium are bronchial asthma, lung cancer, nasal ulcers, skin allergies, carcinogenicity, and genotoxicity. To protect from these adverse effects, WHO has suggested a provisional guideline value of chromium as 0.05 mg/L until further information is available and revalued.

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Malati, M. A., und A. Sear. „Oxidations by manganese(III)—II. Oxidation of chromium(III)“. Polyhedron 8, Nr. 13-14 (Januar 1989): 1874–75. http://dx.doi.org/10.1016/s0277-5387(00)80680-4.

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Peng, Hao, Jing Guo, Gang Li, Qinzhe Cheng, Yuju Zhou, Zuohua Liu und Changyuan Tao. „Highly efficient oxidation of chromium (III) with hydrogen peroxide in alkaline medium“. Water Science and Technology 79, Nr. 2 (15.01.2019): 366–74. http://dx.doi.org/10.2166/wst.2019.056.

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Abstract Many technologies have been proposed to oxidize chromium, such as roasting-water leaching technology and hydrometallurgical methods such as pressure oxidative leaching coupled with oxygen, ozone, permanganate and ferrate, but the problems associated with the high temperature, low overall resource utilization efficiency, high energy consumption, and the environmental pollution, still remain unsolved. This paper focuses on the oxidation process of chromium (III) with hydrogen peroxide (H2O2) in an alkaline medium. The effect of parameters including dosage of H2O2, dosage of NaOH, reaction time, reaction temperature and stirring rate on the oxidation efficiency of chromium were investigated. The oxidation efficiency was significantly affected by the dosage of H2O2 and NaOH, reaction time and reaction temperature took second place; last was the stirring rate. Oxidation efficiency was nearly 100% under the optimal conditions: volume ratio of H2O2 to mass of Cr2(SO4)3 of 2.4 mL/g, mass ratio of NaOH to Cr2(SO4)3 0.6 g/g, reaction time of 90 min, reaction temperature of 90 °C and stirring rate of 500 rpm.

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Hasure, Appasaheb M., und Gavisiddappa S. Gokavi. „Chromium(VI), chromium(V) and chromium(IV) oxidation of 12-tungstocobaltate(II)“. Transition Metal Chemistry 29, Nr. 3 (April 2004): 231–37. http://dx.doi.org/10.1023/b:tmch.0000020348.76720.17.

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Kuhn, Anselm T., und Robert Clarke. „Electrolytic oxidation of chromium salts“. Journal of Applied Chemistry and Biotechnology 26, Nr. 1 (29.05.2007): 407–18. http://dx.doi.org/10.1002/jctb.5020260161.

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Berthod, Patrice, Dame Assane Kane und Lionel Aranda. „Oxidation of a 2wt.%Hf–doped (Ta,C)-rich nickel–based alloy between 1100 and 1250°C“. Bulletin of Scientific Research 4, Nr. 2 (30.11.2022): 24–34. http://dx.doi.org/10.54392/bsr2224.

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In this work, an alloy based on nickel, rich in chromium and designed to be reinforced by MC carbides thanks to the presence of 4wt.% Ta and 2wt.% Hf, was elaborated by conventional casting and exposed to air at three temperatures ranging from 1100 to 1250°C, with follow up of the mass changes due to oxidation. The as–cast microstructure is composed of a dendritic matrix and of eutectic carbides of two types. The major type is (Ta,Hf)C carbide and a minor type is chromium carbide. The isothermal mass gains are slow and their kinetics are of a parabolic type at all temperatures. The alloy demonstrated a chromia–forming behavior in all cases, with the development of an external continuous chromia scale and an internal layer of complex oxide Cr(Ta,Hf)O4. The stability of the external scale during cooling was dependent on the quantity of oxides isothermally formed, i.e. on the oxidation temperature for a given duration. The behavior of the alloy in isothermal oxidation at the considered temperatures is satisfactory but solutions must be found for improving the resistance against cyclic oxidation for the highest temperatures.

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Dillon, Carolyn T., Peter A. Lay, Antonio M. Bonin, Nicholas E. Dixon und Yousif Sulfab. „DNA Interactions and Bacterial Mutagenicity of Some Chromium(III) Imine Complexes and their Chromium(V) Analogues. Evidence for Chromium(V) Intermediates in the Genotoxicity of Chromium(III)“. Australian Journal of Chemistry 53, Nr. 5 (2000): 411. http://dx.doi.org/10.1071/ch00006.

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The in vitro DNA interactions and bacterial mutagenicities of cis-[CrIII(phen)2(OH2)2]3+ and trans-[CrIII(salen)(OH2)2]+ and their CrV analogues are reported. At pH 3.3, cis-[Cr(phen)2(OH2)2]3+ (0.02–2.0 mM) causes negatively supercoiled pUC9 DNA to smear on agarose gels, with substantial precipitation in the well at ≥1.0 mM. Much weaker interactions between CrIII and DNA were apparent at pH 7.4. The interactions between DNA and CrV phen complexes (0.5 mM total Cr, pH 3.3) generated by oxidation of cis-[Cr(phen)2(OH2)2]3+ (for 10–30 min) resulted in almost complete nicking of form I DNA to forms II and III DNA. Nicking of form I DNA (≥80%) was also apparent at pH 7.4 following reaction of DNA with PbO2-oxidized [Cr(phen)2(OH2)2]3+ (2 mM Cr). Interactions between trans-[CrIII(salen)(OH2)2]+ and DNA were weaker than those of the CrIII phen complex at both pH 3.3 and 7.4. The CrV salen derivative (0.5 mM total Cr) caused the disappearance of form I DNA at oxidation times of ≥10 min and at pH 3.3 with substantial cleavage. While oxidation of [Cr(salen)(OH2)2]+ by PbO2 was not observed at pH 7.4, the complex was oxidized by iodosobenzene to produce short-lived [CrO(salen)]+ that caused DNA smearing on the agarose gel. In bacterial mutagenicity assays, the CrIII imine complexes and their CrV analogues produced similar mutagenic responses, which were believed to be due to the instabilities of the CrV species in the bacterial growth medium. While the spectrum of the mutagenic activities differed between the chromium phen and salen complexes, both exhibited greatest mutagenicity in Salmonella typhimurium TA102. These data suggest that CrV species, generated in vivo by cellular oxidative enzymes, may be responsible for CrIII-induced mutagenesis.

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Sumner, Edward R., Anupama Shanmuganathan, Theodora C. Sideri, Sylvia A. Willetts, John E. Houghton und Simon V. Avery. „Oxidative protein damage causes chromium toxicity in yeast“. Microbiology 151, Nr. 6 (01.06.2005): 1939–48. http://dx.doi.org/10.1099/mic.0.27945-0.

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Oxidative damage in microbial cells occurs during exposure to the toxic metal chromium, but it is not certain whether such oxidation accounts for the toxicity of Cr. Here, a Saccharomyces cerevisiae sod1Δ mutant (defective for the Cu,Zn-superoxide dismutase) was found to be hypersensitive to Cr(VI) toxicity under aerobic conditions, but this phenotype was suppressed under anaerobic conditions. Studies with cells expressing a Sod1p variant (Sod1H46C) showed that the superoxide dismutase activity rather than the metal-binding function of Sod1p was required for Cr resistance. To help identify the macromolecular target(s) of Cr-dependent oxidative damage, cells deficient for the reduction of phospholipid hydroperoxides (gpx3Δ and gpx1Δ/gpx2Δ/gpx3Δ) and for the repair of DNA oxidation (ogg1Δ and rad30Δ/ogg1Δ) were tested, but were found not to be Cr-sensitive. In contrast, S. cerevisiae msraΔ (mxr1Δ) and msrbΔ (ycl033cΔ) mutants defective for peptide methionine sulfoxide reductase (MSR) activity exhibited a Cr sensitivity phenotype, and cells overexpressing these enzymes were Cr-resistant. Overexpression of MSRs also suppressed the Cr sensitivity of sod1Δ cells. The inference that protein oxidation is a primary mechanism of Cr toxicity was corroborated by an observed ∼20-fold increase in the cellular levels of protein carbonyls within 30 min of Cr exposure. Carbonylation was not distributed evenly among the expressed proteins of the cells; certain glycolytic enzymes and heat-shock proteins were specifically targeted by Cr-dependent oxidative damage. This study establishes an oxidative mode of Cr toxicity in S. cerevisiae, which primarily involves oxidative damage to cellular proteins.

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Cummings, Charles Y., Gary A. Attard, John M. Mitchels und Frank Marken. „Surface State Trapping and Mobility Revealed by Junction Electrochemistry of Nano-Cr2O3“. Australian Journal of Chemistry 65, Nr. 1 (2012): 65. http://dx.doi.org/10.1071/ch11382.

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Hydrous chromium oxide nanoparticles (~15 nm diameter) are assembled from a colloidal solution onto tin-doped indium oxide (ITO) substrates by layer-by-layer electrostatic deposition with aqueous carboxymethyl-cellulose sodium salt binder. Calcination produces purely inorganic mesoporous films (average thickness increase per layer of 1 nm) of chromia Cr2O3. When immersed in aqueous carbonate buffer at pH 10 and investigated by cyclic voltammetry, a chemically reversible oxidation is observed because of a conductive layer at the chromia surface (formed during initial potential cycling). This is attributed to a surface CrIII/IV process. At more positive potentials higher oxidation states are accessible before film dissolution. The effects of film thickness and pH on voltammetric responses are studied. X-Ray photoelectron spectroscopy (XPS) evidence for higher chromium oxidation states is obtained. ITO junction experiments are employed to reveal surface conduction by CrIII/IV and CrIV/V ‘mobile surface states’ and an estimate is obtained for the apparent CrIII/IV charge surface diffusion coefficient Dapp = 10–13 m2 s–1. The junction experiment distinguishes mobile surface redox sites from energetically distinct deeper-sitting ‘trapped states’.

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Singh, Veer, Nidhi Singh, Manisha Verma, Rashmi Kamal, Ritesh Tiwari, Mahesh Sanjay Chivate, Sachchida Nand Rai et al. „Hexavalent-Chromium-Induced Oxidative Stress and the Protective Role of Antioxidants against Cellular Toxicity“. Antioxidants 11, Nr. 12 (30.11.2022): 2375. http://dx.doi.org/10.3390/antiox11122375.

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Hexavalent chromium is a highly soluble environmental contaminant. It is a widespread anthropogenic chromium species that is 100 times more toxic than trivalent chromium. Leather, chrome plating, coal mining and paint industries are the major sources of hexavalent chromium in water. Hexavalent chromium is widely recognised as a carcinogen and mutagen in humans and other animals. It is also responsible for multiorgan damage, such as kidney damage, liver failure, heart failure, skin disease and lung dysfunction. The fate of the toxicity of hexavalent chromium depends on its oxidation state. The reduction of Cr (VI) to Cr (III) is responsible for the generation of reactive oxygen species (ROS) and chromium intermediate species, such as Cr (V) and Cr (IV). Reactive oxygen species (ROS) are responsible for oxidative tissue damage and the disruption of cell organelles, such as mitochondria, DNA, RNA and protein molecules. Cr (VI)-induced oxidative stress can be neutralised by the antioxidant system in human and animal cells. In this review, the authors summarise the Cr (VI) source, toxicity and antioxidant defence mechanism against Cr (VI)-induced reactive oxygen species (ROS).

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Royer, Laurent, Stéphane Mathieu, Christophe Liebaut und Pierre Steinmetz. „Oxidation and Nitridation of Pure Chromium at Elevated Temperature in Synthetic Air – Effect of Silicon Addition“. Materials Science Forum 595-598 (September 2008): 1047–55. http://dx.doi.org/10.4028/www.scientific.net/msf.595-598.1047.

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The oxidation and nitridation of pure chromium and of chromium alloys containing 0.5 to 5at% silicon was investigated at 1300°C in several atmospheres. Global methods like thermogravimetry were associated to thickness measurements and microstructural characterisation to evaluate oxidation mechanisms. The contribution of nitridation to weight gain during high temperature exposure is discussed, examining nitride volume fraction. Experiments demonstrate that the presence of nitrogen in the substrate is always consecutive to a breakdown of the oxide layer and does not result from diffusion through the Cr2O3 layer. Silicon, when present in chromium solid solution, slows down the oxidation kinetics and limits the progression of nitrogen in the chromium lattice and at grain boundaries. The absence of the Cr2N layer beneath the metal/oxide interface does not benefit to the adherence of the oxide scale. Oxidation of silicon in chromium leads to the formation of discontinuous particles of SiO2 at the metal/oxide interface, at the grain boundaries and dispersed in the bulk in the alloy sub-surface.

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Łącz, Agnieszka, und Ewa Drożdż. „Porous Y and Cr–doped SrTiO3 materials—electrical and redox properties“. Journal of Solid State Electrochemistry 23, Nr. 10 (16.09.2019): 2989–97. http://dx.doi.org/10.1007/s10008-019-04386-3.

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Abstract Highly porous materials in the Sr0.96Y0.04Ti1-xCrxO3 system (where x = 0, 2, 4, 8 mol.%) were obtained by wet synthesis method. The structural and electrical properties of these materials were determined together with the ability to participate in oxidation/reduction reactions, since yttrium is responsible for high electrical conductivity in reducing atmosphere and chromium is a factor affecting the catalytic properties. For the material with the highest assumed amount of chromium, the small content of an additional phase (Cr2O3) was observed. SrTiO3 lattice parameters together with the results of temperature-programmed reduction (TPR) and temperature-programmed oxidation (TPOx) tests and Seebeck coefficient measurements allowed to determine the oxidation states of chromium in the received materials. It was shown that introduction of Y into strontium sublattice stabilises the strontium titanate structure and affects the oxidation state of chromium incorporated into the titanium sublattice. The defect structure in Sr0.96Y0.04Ti1-xCrxO3 system is a complex problem, since yttrium is a donor type dopant and chromium due to the possible +3 and +6 oxidation states can be considered both acceptor and donor type one. Thus, a change in the conduction mechanism with the chromium content was observed in both oxidising and reducing atmosphere.

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Signorella, Sandra, Marcela Rizzotto, Ver�nica Daier, Mar�a I. Frascaroli, Claudia Palopoli, D�bora Martino, Azzedine Bousseksou und Luis F. Sala. „Comparative study of oxidation by chromium(V) and chromium(VI)“. Journal of the Chemical Society, Dalton Transactions, Nr. 8 (1996): 1607. http://dx.doi.org/10.1039/dt9960001607.

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29

Botavina, M., C. Barzan, A. Piovano, L. Braglia, G. Agostini, G. Martra und E. Groppo. „Insights into Cr/SiO2 catalysts during dehydrogenation of propane: an operando XAS investigation“. Catalysis Science & Technology 7, Nr. 8 (2017): 1690–700. http://dx.doi.org/10.1039/c7cy00142h.

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In situ and operando XAS spectroscopic methods were applied to monitor the variations in the oxidation state and in the local structure of the chromium sites in a 2.0Cr/SiO_2-DHS catalyst during propane dehydrogenation under non-oxidative and different oxidative conditions.

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Tumolo, Marina, Valeria Ancona, Domenico De Paola, Daniela Losacco, Claudia Campanale, Carmine Massarelli und Vito Felice Uricchio. „Chromium Pollution in European Water, Sources, Health Risk, and Remediation Strategies: An Overview“. International Journal of Environmental Research and Public Health 17, Nr. 15 (28.07.2020): 5438. http://dx.doi.org/10.3390/ijerph17155438.

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Chromium is a potentially toxic metal occurring in water and groundwater as a result of natural and anthropogenic sources. Microbial interaction with mafic and ultramafic rocks together with geogenic processes release Cr (VI) in natural environment by chromite oxidation. Moreover, Cr (VI) pollution is largely related to several Cr (VI) industrial applications in the field of energy production, manufacturing of metals and chemicals, and subsequent waste and wastewater management. Chromium discharge in European Union (EU) waters is subjected to nationwide recommendations, which vary depending on the type of industry and receiving water body. Once in water, chromium mainly occurs in two oxidation states Cr (III) and Cr (VI) and related ion forms depending on pH values, redox potential, and presence of natural reducing agents. Public concerns with chromium are primarily related to hexavalent compounds owing to their toxic effects on humans, animals, plants, and microorganisms. Risks for human health range from skin irritation to DNA damages and cancer development, depending on dose, exposure level, and duration. Remediation strategies commonly used for Cr (VI) removal include physico-chemical and biological methods. This work critically presents their advantages and disadvantages, suggesting a site-specific and accurate evaluation for choosing the best available recovering technology.

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Cameron, T. Stanley, Jason AC Clyburne, Pramod K. Dubey, J. Stuart Grossert, K. Ramaiah, J. Ramanatham und Sergei V. Sereda. „Compounds of chromium(VI): The pyridine chromic anhydride complex, benzimidazolinium dichromate, and three 2-alkyl-1H-benzimida -zolinium dichromates“. Canadian Journal of Chemistry 81, Nr. 6 (01.06.2003): 612–19. http://dx.doi.org/10.1139/v03-042.

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Pyridine, when allowed to react with chromic anhydride under strictly anhydrous conditions, gives the known, very air-sensitive, crystalline 2:1 Lewis acidbase complex 1. The crystal structure has now been successfully determined. When benzimidazole and three 2-alkyl-1H-benzimidazoles were treated with chromium trioxide in aqueous acetic acid, crystalline dichromate salts (25) were readily formed. These salts consist of dichromate anions linked to the cations by hydrogen bonds of the type NH···O. The chromium atoms have distorted tetrahedral environments, with the CrO distances being typical for dichromate anions. In the cases of the 2-methyl and 2-ethyl salts, the anions are disordered about a centre of inversion. The hydrogen bonding arrangements are discussed and the structures are compared with other oxygenated chromium(VI) species. The dichromate salts are useful selective oxidants for a range of primary and secondary alcohols; examples of these reactions are reported.Key words: chromium(VI), pyridine chromium trioxide complex, benzimidazolinium dichromate salts, controlled oxidation of alcohols.

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Pujilaksono, Bagas. „THE DEGRADATION OF THE PROTECTIVE SCALE ON BINARY FeCr ALLOYS (Fe-2.25Cr, Fe-10Cr, Fe-18Cr AND Fe-25Cr) IN CO2 AND IN CO2 + H2O ENVIRONMENT AT 600oC“. Scientific Contributions Oil and Gas 39, Nr. 1 (01.05.2016): 15–29. http://dx.doi.org/10.29017/scog.39.1.530.

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The oxidation behaviour of the binary alloys Fe-2.25, Fe-10Cr, Fe-18Cr and Fe-25Cr in dry and wet O2 at 600oC is investigated by isothermal exposures of carefully polished samples for up to 168 hours. The oxidized samples are investigated gravimetrically and the oxides formed are studied by X-ray diffraction. X-ray photoelectron spectroscopy is used for depth pro􀂿 ling of the thin oxides. The scale surface is imaged by SEM. Cross sections through the scale are analyzed by SEM/EDX for imaging and for measuring the chemical composition. The oxidation behavior of the four FeCr alloys is intermediate between those of iron and chromium. Fe-2.25Cr oxidizes in a way similar to iron in both environments, forming a poorly protective scale consisting of FeCr spinel at the bottom, magnetite in the middle and a hematite cap layer. In dry O2, Fe-10Cr, Fe-18Cr and Fe-25Cr form a thin and protective (Fe,Cr)2O3 oxide similar to the chromia 􀂿 lm formed on pure chromium. In wet O2, Fe-10Cr, Fe-18Cr and Fe-25Cr initially form the same kind of protective oxide 􀂿 lm as in dry conditions. After an incubation time that depends on alloy chromium content, all three alloys go into breakaway oxidation and form thick, poorly protective scales similar to those formed on Fe-2.25Cr. Breakaway oxidation in wet O2 is triggered by the evaporation of CrO2(OH)2 from the protective (Fe,Cr)2O3 oxide.

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Sole, Kathryn C., Michael B. Mooiman und Michael E. Brown. „Oxidation kinetics of chromium(III) chloride“. Journal of the Chemical Society, Faraday Transactions 86, Nr. 3 (1990): 525. http://dx.doi.org/10.1039/ft9908600525.

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Meier-Callahan, Alexandre E., Angel J. Di Bilio, Liliya Simkhovich, Atif Mahammed, Israel Goldberg, Harry B. Gray und Zeev Gross. „Chromium Corroles in Four Oxidation States“. Inorganic Chemistry 40, Nr. 26 (Dezember 2001): 6788–93. http://dx.doi.org/10.1021/ic010723z.

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Chen, Hong-Ying, und Fu-Hsing Lu. „Oxidation behavior of chromium nitride films“. Thin Solid Films 515, Nr. 4 (Dezember 2006): 2179–84. http://dx.doi.org/10.1016/j.tsf.2006.06.039.

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Moon, Jae-Jin, Deug-Joong Kim und Dong-Bok Lee. „High temperature oxidation of chromium nitrides“. Metals and Materials International 8, Nr. 2 (April 2002): 211–14. http://dx.doi.org/10.1007/bf03027020.

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Gokavi, G. S., und J. R. Raju. „Chromium(VI) oxidation of thallium(I)“. Polyhedron 6, Nr. 9 (Januar 1987): 1721–25. http://dx.doi.org/10.1016/s0277-5387(00)86542-0.

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Lee, Dong Bok, und G. Simkovich. „Oxidation of molybdenum-chromium-palladium alloys“. Oxidation of Metals 34, Nr. 1-2 (August 1990): 13–22. http://dx.doi.org/10.1007/bf00664337.

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Oryshich, I. V., N. E. Poryadchenko, I. G. Slys’, N. P. Brodnikovskii und A. V. Golovash. „Air oxidation of chromium-based composites“. Powder Metallurgy and Metal Ceramics 46, Nr. 3-4 (März 2007): 189–93. http://dx.doi.org/10.1007/s11106-007-0030-8.

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Bondar', E. R. „Kinetics of oxidation of chromium steel“. Soviet Materials Science 23, Nr. 3 (1987): 306–8. http://dx.doi.org/10.1007/bf00720897.

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Shinata, Y., und Y. Nishi. „NaCl-induced accelerated oxidation of chromium“. Oxidation of Metals 26, Nr. 3-4 (Oktober 1986): 201–12. http://dx.doi.org/10.1007/bf00659184.

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Zheng, Tao, und Jing Tao Han. „High Temperature Oxidation Behavior of SUS310S Austenitic Stainless Steel“. Advanced Materials Research 941-944 (Juni 2014): 212–15. http://dx.doi.org/10.4028/www.scientific.net/amr.941-944.212.

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The oxidation behavior of SUS310S austenitic stainless steels was studied in isothermal conditions at different temperatures between 800oC and 1100oC for 96h in air. The oxidation kinetics was analyzed, the surface and cross-section of the oxide scale grown by oxidation were characterized by using scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray diffusion (XRD) and X-ray photoelectron spectroscopy (XPS). The SUS310S steel has high oxidation resistance at 800oC and with the increase of the temperature, the parabolic rate constants is constantly increasing. Examination of the morphology and composition of oxide layers reveals a double-layer structure, The inner layer is mainly chromium oxide (Cr2O3) and is covered by an uneven thinness outer layer of manganese-chromium or iron-chromium spinel oxide.

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Riffard, F., Henri Buscail, F. Rabaste, Christophe Issartel und Sébastien Perrier. „Effect of Phosphoric Acid Treatment on Isothermal High Temperature Oxidation Behaviour of AISI 304 Stainless Steel at 800°C“. Defect and Diffusion Forum 323-325 (April 2012): 359–64. http://dx.doi.org/10.4028/www.scientific.net/ddf.323-325.359.

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Phosphoric acid treatment is used as a way to improve the high temperature oxidation resistance of a chromia-forming AISI 304 steel. Chromia-forming steels are excellent candidates to resist to high temperature oxidizing atmospheres because of the formation of protective oxide scales. The oxide scale growth mechanisms are studied by exposing phosphoric acid-treated and untreated 304 steel samples to high temperature conditions in air. The analyses were carried out by means of thermogravimetry, andin situX-ray diffraction (XRD). The experimental results show that the phosphoric acid treatment does not have a beneficial effect on cyclic high temperature oxidation (up to 70h of the oxidation test) of AISI 304 steel because of growth of a layer mainly formed by external cation diffusion which grows very quickly. The isothermal high temperature oxidation of this steel at 800°C in air shows a very fast initial iron oxidation towards the external interface, allowing to chromium element to be more available to the internal interface to form a continuous chromia layer, thus causing the establishment of a parabolic oxidation regime and leading to a beneficial reduction of the oxidation rate (after 70h of the oxidation test).

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Signorella, Sandra R., Mabel I. Santoro, Mirta N. Mulero und Luis F. Sala. „Oxidation of D-gluconic acid by chromium(VI) in perchloric acid“. Canadian Journal of Chemistry 72, Nr. 2 (01.02.1994): 398–402. http://dx.doi.org/10.1139/v94-061.

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The oxidation of gluconic acid by chromium(VI) in perchloric acid has been found to follow the rate law: −d[CrVI]/dt = (k′1 + k′2[GA])[H+]2[CrVI], where k′1 = (7.1 ± 0.2) × 10−4 M−2 s−1 and k′2 = (9.4 ± 0.2) × 10−2 M−3 s−1. This rate law corresponds to the reaction leading to the formation of 2-ketogluconic acid by C—H cleavage when a 20-fold or higher excess of acid over chromium(VI) is employed. Buildup and decay of chromium(V) intermediates accompany the decay of chromium(VI). Chromium(V) rates of decay are similar or slower than those of chromium(VI), as observed by electron paramagnetic resonance (epr) and visible spectrophotometry.

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KANG, M. „Methylene chloride oxidation on oxidative carbon-supported chromium oxide catalyst“. Applied Catalysis A: General 266, Nr. 2 (Juli 2004): 163–72. http://dx.doi.org/10.1016/j.apcata.2004.02.041.

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Mardwita, Mardwita, Eka Sri Yusmartini und Nidya Wisudawati. „Effects of Cobalt and Chromium Loadings to The Catalytic Activities of Supported Metal Catalysts in Methane Oxidation“. Bulletin of Chemical Reaction Engineering & Catalysis 15, Nr. 1 (15.01.2020): 213–20. http://dx.doi.org/10.9767/bcrec.15.1.6320.213-220.

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A series of alumina supported cobalt and chromium catalysts with different metal loadings were prepared by impregnation method. Six types of alumina supported cobalt and chromium catalysts contained 5 wt%, 10 wt%, and 15 wt% loadings were produced and tested in methane oxidation. The catalysts were characterized by using x-ray diffraction (XRD) and carbon monoxide chemisorption (CO chemisorption). The XRD results do not confirmed any features of cobalt and chromium metal. The metal sizes for both catalysts were larger in high loading as shown by CO chemisorption results. Methane conversion results showed that the conversion increases with increasing the metal loading, however supported chromium catalysts were higher in activities compared to supported cobalt catalysts. Thermal stability tests on 15 wt% Co/Al and 15 wt% Cr/Al catalyst showed that supported chromium catalyst is more stable and maintain the particle size due to its strong interaction with support, while supported cobalt catalyst decrease in methane conversion due to deactivation of the catalyst. Copyright © 2020 BCREC Group. All rights reserved

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Brylewski, Tomasz, und Kazimierz Przybylski. „Perovskite and Spinel Functional Coatings for SOFC Metallic Interconnects“. Materials Science Forum 595-598 (September 2008): 813–22. http://dx.doi.org/10.4028/www.scientific.net/msf.595-598.813.

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The oxidation kinetics, electrical properties, microstructure and chromium vaporization effects of the oxide products formed on Fe-25 wt.-%Cr steel uncoated and coated with films of (La,Sr)CrO3, (La,Sr)CoO3, (La,Sr)(Co,Fe)O3, Mn1.5Cr1.5O4 and MnCo2O4 in air and the Ar-H2-H2O gas mixture at 1023−1173 K for up to 840 h with regard to their application as SOFC metallic interconnect were investigated. To improve poor electrical conductivity of chromia scales and to suppress chromium vaporization from this scale grown on uncoated steel during oxidation, the perovskite and spinel thick films composed of paste prepared via co-precipitation-calcination and ultrasonic spray pyrolysis methods were applied. Perovskite and spinel coatings decreased the volatilization rate of chromia species in comparison with the value of this parameter corresponding to oxide scales built mainly of chromia formed on uncoated steel. Microstructure investigations by the SEM-EDS method and electrical resistance measurements revealed the significant influence of the formation of multilayer reaction products at the steel/coating interface on the electrical properties of the composite materials used for the construction of the SOFC metallic interconnect.

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Mamedova, M. T. „EFFECT OF CARBON DIOXIDE ON OXIDATIVE ETHYLBENZENE DEHYDROGENATION IN THE PRESENCE OF ALUMINUM-CHROMIUM CATALYSTS“. Azerbaijan Chemical Journal, Nr. 2 (29.06.2021): 69–79. http://dx.doi.org/10.32737/0005-2531-2021-2-69-79.

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In order to create a more efficient process for the production of styrene from ethylbenzene by selective oxidation of the resulting hydrogen, model aluminum-chromium catalysts with different modifier (Cu) contents were prepared, and O2, CO2 and a mixture of CO2:air were used as an oxidant. It has been es-tablished that the process of obtaining of styrene from ethylbenzene on alumochromic catalysts is characterized by a high intensity. Alumochromic catalysts modified by Cu and promoted by 15 mass.% K2CO3 in the presence of carbon dioxide increase the conversion of ethylbenzene by 14%, and the selectivity of the formation of styrene by 10% as a result of the transferring dehydrogenation of compaction products to the products of oxidative compaction. The presence of oxygen in the oxidizing mixture CO2:air blocks the participation of carbon dioxide in the selective oxidation of hydrogen isolating at the dehydrogenation of ethylbenzene. It has been established that the most selective alumochromic catalysts in the oxidative dehydrogenation of ethylbenzene to styrene contain 1.5–2.5 mass.% of the modifying component (Cu)

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Brodnikovskii, N. P., I. V. Oryshich, N. E. Poryadchenko, T. L. Kuznetsova, N. D. Khmelyuk und E. A. Rokitskaya. „Resistance of titanium– chromium and zirconium–chromium alloys to air oxidation“. Powder Metallurgy and Metal Ceramics 49, Nr. 7-8 (Dezember 2010): 454–59. http://dx.doi.org/10.1007/s11106-010-9257-x.

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Komratov, G. N. „Oxidation kinetics of binary chromium-titanium carbide and chromium carbide powders“. Powder Metallurgy and Metal Ceramics 38, Nr. 9-10 (September 1999): 472–76. http://dx.doi.org/10.1007/bf02676063.

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