Journal articles on the topic 'Chromium'
To see the other types of publications on this topic, follow the link: Chromium.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 journal articles for your research on the topic 'Chromium.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse journal articles on a wide variety of disciplines and organise your bibliography correctly.
1
Liu, Yan, Mao Fa Jiang, and De Yong Wang. "Reduction Feature and Selection Principle of Chromium Ore for Stainless Steelmaking in a Smelting Reduction Converter." Applied Mechanics and Materials 142 (November 2011): 161–64. http://dx.doi.org/10.4028/www.scientific.net/amm.142.161.
Full textAbstract:
This paper starts with the mineral structure, reducing properties of chromium ore and the physical and chemical properties of chromium oxide and discusses the requirements of the chemical composition of chromite and confirms the selection principle of chromium ore and reducing agent of chromium ore smelting reduction. The chemical compositions of the available chromite request the relatively high contents of chromium and iron, the lower contents of Al2O3, MgO and P in gangue and the lower Cr/Fe ratio in keeping with the case of high chromium. Chromoium ore in South Africa is considered to be suitable for smelting stainless steel crude melts in a smelting reduction converter. From the reducing power and economy angle, carbon as a reducing agent is more suited to reducing chromium ore.
2
Martynenko, V. V., P. O. Kushchenko, I. G. Shulyk, Yu Ye Mishnyova, K. I. Kushchenko, and Yu O. Krakhmal. "Properties dependence of chromia and alumina-chromia-zirconia-silica refractories with a mass fraction of 30 % Cr2O3 on the type of chromium oxide." Scientific research on refractories and technical ceramics 121 (December 30, 2021): 23–35. http://dx.doi.org/10.35857/2663-3566.121.03.
Full textAbstract:
In JSC “URIR named after A. S. Berezhnoy” chromia refractories for the lining of pool and feeder of glass-making furnaces for the production of glass fiber from E glass, which are in contact with the glass melt, and alumina-chromia-zirconia-silica refractories with 30 % Cr2O3 for service in the topsides of these furnaces, in areas affected by components of the glass batch and glass melt, have been developed and manufactured. The main raw material for the chromia products manufacturing is metallurgical chromium oxide. In the manufacture of alumina-chromia-zirconia-silica products, metallurgical chromium oxide or a mixture of metallurgical and pigment chromium oxide in a ratio of 2 : 1 is used as the chromium oxide component of the batch. The testing of new materials, such as a new grade of chromium oxide, in the technologies of chromia and alumina-chromia-zirconia-silica refractories is relevant.
The effect of a new grade of chromium oxide on the properties of chromia refractories has been investigated. It was found that samples of a new grade of chromium oxide, pressed at optimal values of moisture content of the mass and specific pressing pressure, are characterized by a low apparent density of the raw material in comparison with samples made of metallurgical chromium oxide. After firing, samples from chromium oxide of the new grade are not inferior to those of metallurgical chromium oxide in terms of properties, but they have large changes in linear dimensions during firing, which can lead to the formation of cracks, therefore, the issue of obtaining chromia products from mixtures with the replacement of metallurgical chromium oxide with chromium oxide of the new grade in order to increase the apparent density of products requires additional research.
A study on the effect of new grade of chromium oxide on the properties of alumina-chromia-zirconia-silica refractories with a content of 30 % Cr2O3 has been carried out. It was established that, in the batch for the manufacture of these refractories, containing metallurgical and pigment chromium oxide, it is possible to completely replace the pigment chromium oxide with chromium oxide of the new grade or to increase the content in the batch of chromium oxide of the new grade instead of a part of metallurgical chromium oxide to the ratio of metallurgical chromium oxide and chromium oxide of the new grade 1 : 2.
3
Tripathy, Sunil, Y. Murthy, Veerendra Singh, Saeed Farrokhpay, and Lev Filippov. "Improving the Quality of Ferruginous Chromite Concentrates Via Physical Separation Methods." Minerals 9, no. 11 (October 29, 2019): 667. http://dx.doi.org/10.3390/min9110667.
Full textAbstract:
The low chromium-to-iron ratio of chromite ores is an important issue in some chromite deposits. The value of the chromite ore is indeed dictated in the market by its iron, as well as its chromium content. In the present study, a chromite concentrate was reprocessed by gravity (spiral concentrator) and magnetic separation to enhance the chromium-to-iron ratio. Also, detailed characterization studies including automated mineralogy were carried out to better understand the nature of the samples. Enhancing the chromium-to-iron ratio was achieved by using advanced spiral separators which will be discussed in this paper.
4
Xiao, Y. Y., L. J. Wang, S. Y. Liu, X. B. He, and K. C. Chou. "Kinetic mechanism of FeCr2O4 reduction in carbon-containing iron melt." Journal of Mining and Metallurgy, Section B: Metallurgy, no. 00 (2023): 10. http://dx.doi.org/10.2298/jmmb230215010x.
Full textAbstract:
Direct alloying of chromium by chromite attracts a lot of interest for its superiority in energy-saving and process simplification. The knowledge of chromium alloying by reduction of FeCr2O4, the main component of chromite, is key to understanding the mechanism of chromium alloying from chromite. The effect of melt composition (carbon and chromium addition) and temperature on the reduction of FeCr2O4 by carbon-containing iron melt was studied. The higher the carbon content is in the melt, the higher chromium recovery is obtained. Similarly, the higher temperature is favourable for the reduction of FeCr2O4. The reduction of FeCr2O4 was impeded by chromium addition due to the lower activity of carbon resulting from the strong attraction between carbon and chromium. The kinetics of FeCr2O4 reduction by carbon dissolving in iron melt were investigated, and the results indicated that the controlling step is the chemical reaction at the FeCr2O4/melt interface at 1823K. And the calculated activation energy for the chemical reaction is 392.82 kJ/mol.
5
Kajitvichyanukul, Puangrat, and Chulaluck Changul. "PHOTOCATALYTIC REMOVAL OF TR I- AND HEXA-VALENT CHROMIUM IONS FROM CHROME-ELECTROPL ATING WASTEWATER." ASEAN Journal on Science and Technology for Development 22, no. 4 (November 11, 2017): 355. http://dx.doi.org/10.29037/ajstd.171.
Full textAbstract:
A novel technique based on photocatalysis was applied to eliminate chromium ions, a toxic hazardous environmental pollutant. The photoreduction of each species of chromium (total, hexavalent, and trivalent chromiums) from chrome-electroplating wastewater was investigated using a titanium dioxide suspension under irradiation by a low-pressure mercury lamp. The initial concentration of total chromium was 300 mg/l. The applied conditions were the direct photocatalytic reduction process at pH 3.65 and the indirect photocatalytic reduction with added hole scavengers at the same solution pH. Results from both processes were comparatively discussed. Result show that chromium was not efficiently removed by direct photoreduction. In contrast, with the adding of hole scavengers, which were formate ions, the photoreduction of chromium was very favorable. Both hexavalent and trivalent chromiums were efficiently removed. The photocatalytic mechanism is purposed in this study.
6
Hu, X., H. Wang, L. Teng, and S. Seetharaman. "Direct chromium alloying by chromite ore with the presence of metallic iron." Journal of Mining and Metallurgy, Section B: Metallurgy 49, no. 2 (2013): 207–15. http://dx.doi.org/10.2298/jmmb120815015h.
Full textAbstract:
Direct chromium alloying by chromite ore in EAF operation is a promising process in stainless steel production, which has the advantage of resource-saving, energy-saving, and environment-friendly. In the present investigation, iron, carbon, and chromite ore mixture (Fe+C+FeCr2O4) were chosen as the precursor for direct chromium alloying. Thermogravimetric Analysis (TGA) experiments were carried out to investigate the effect of iron content on the reduction kinetics, and the results show that the presence of metallic iron in the precursor will increase the reduction rate of chromite. Up-scaling experiments (100 g and 500 g scale) have been carried out in the induction furnace to further test the effectiveness of using industrial chromite ore for direct chromium alloying. The induction furnace tests confirmed the necessity of adjusting composition of the slags to ensure high yield of chromium in the final products; and chromium yield can reach 90%.
7
Kanari, Ndue, Eric Allain, Lev Filippov, Seit Shallari, Frédéric Diot, and Fabrice Patisson. "Reactivity of Low-Grade Chromite Concentrates towards Chlorinating Atmospheres." Materials 13, no. 20 (October 9, 2020): 4470. http://dx.doi.org/10.3390/ma13204470.
Full textAbstract:
The most economically important iron-chromium bearing minerals is chromite. In natural deposits, iron(II) is frequently substituted by magnesium(II) while chromium(III) is replaced by aluminum(III) and/or iron(III) forming a complex chromium bearing material. The majority of mined chromite is intended for the production of ferrochrome which requires a chromite concentrate with high chromium-to-iron ratio. Found mostly in the spinel chromite structure, iron cannot be removed by physical mineral processing methods. In this frame, the present work deals with the reaction of chlorine and chlorine+oxygen with selected samples of chromite concentrates for assessing the reactivity of their components towards chlorinating atmosphere, allowing the preferential removal of iron, hence meeting the chromite metallurgical grade requirements. Isothermal thermogravimetric analysis was used as a reliable approach for the kinetic reactivity investigation. Results indicated a wide difference in the thermal behavior of chromite constituents in a chlorinating atmosphere when considering their respective values of apparent activation energy oscillating from about 60 to 300 kJ/mol as a function of the sample reacted fraction. During the chromite treatment by chlorine in presence of oxygen, chromium was recovered as liquid chromyl chloride by condensation of the reaction gas phase.
8
SHIRYAEV, Pavel Borisovich, and Nadezhda Vladimirovna VAKHRUSHEVA. "Genesis of podiform chromitites – a review of models." NEWS of the Ural State Mining University 1, no. 2 (June 15, 2020): 20–29. http://dx.doi.org/10.21440/2307-2091-2020-2-20-29.
Full textAbstract:
Relevance of the work. Research aimed at identification of genesis of chromium ores in alpine-type hyperbasites has been conducted by scientists (geologists, petrologists and geochemists) around the world for more than a century. Nevertheless, the issue of their origin remains debatable to this day. The purpose of the work is to highlight the main stages of the development of scientific ideas about the genesis of chromian mineralization in alpinotype hyperbasites; to present and summarize the main, most significant and innovative scientific ideas of Russian and foreign experts who have been involved in this issue. Results. The evolution of scientific views on the genesis of chromic mineralization from the second half of the 19th century is traced. In Russia and abroad, its main stages are highlighted. Throughout this period, some ideas dominated that link the formation of concentrations of ore-forming chrome-spinels with its crystallization from magmatic melt. Major discoveries in earth sciences – the emergence of plate tectonics, the discovery of UHP minerals in chromite-bearing ultrabasites, – intensified the scientific search and led to the emergence of alternative models that consider chromitites as products of metasomatism or metamorphism. Particular attention is paid to the results of research by Russian experts, whose scientific contribution to the development of ideas about the genesis of chromium ores is very large and at the same time, from our point of view, underestimated. This work is intended for geologists, petrologists, and experts in the geology of ore deposits dealing with ultramafic, chromic ores, and ophiolite complexes in general.
9
Dong, Guo Ri, and Jian She Liu. "Effects of Trivalent Chromic Ions with Different Concentrations on Settling Volume (SV) of Activated Sludge in the Settling Period of SBR Process." Advanced Materials Research 864-867 (December 2013): 1258–61. http://dx.doi.org/10.4028/www.scientific.net/amr.864-867.1258.
Full textAbstract:
Aiming at the toxicity effect of trivalent chromic ions on activated sludge in SBR process system, by determination of the settling volume SV, the effects of trivalent chromic ions on sludge settling volume SV in the settling period of SBR process was studied. The results show that trivalent chromic ions will make the sludge volume increase under low chromium load. Moreover, the sludge volume will increase with increasing chromium load, but the settling volume of the activated sludge at 30 min begins to increase in waves as chromium load continues to increase. When the chromium load increases to a certain level, the settling volume of the activated sludge at 30 min continues to decline in waves and is finally lower than the sludge settling volume of the contrast system at 30 min. The experiment suggests that trivalent chromic ions have toxicity and flocculation effects to the activated sludge, and the interaction of the two effects leads to the change of the activated sludge in waves as the chromium load increases.
10
Pokhrel, Ganga Raj, and Galaxy Pokhre. "Effect of Chromium on Human-Health: A Review." BMC Journal of Scientific Research 5, no. 1 (December 31, 2022): 27–35. http://dx.doi.org/10.3126/bmcjsr.v5i1.50669.
Full textAbstract:
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.
11
Zhang, Ya Ni, Chang Zheng Xu, Mao Sheng Zheng, and Jie Wu Zhu. "Corrosion Behaviour of Ultra-Fine Grain Chromium Bronze Prepared by Equal-Channel Angular Pressing in Nacl Solution." Advanced Materials Research 194-196 (February 2011): 554–57. http://dx.doi.org/10.4028/www.scientific.net/amr.194-196.554.
Full textAbstract:
The corrosion resistance of Ultra-fine grain (UFG) chromium bronze, prepared by Equal-channel angular pressing (ECAP), was investigated at room temperature and atmospheric pressure by electrochemistry technique and immersion experiment. The electrochemistry experiment showed that ECAP processing don’t change the corrosion nature of chromiun bronze, the corrosion potential of UFG chromium bronze is a little more positive than that of CG chromium bronze, the differences are in the range of 10mV-20mV. Meantime, the immersion experiment showed that the UFG chromium bronze is more resistant to corrosion than its CG counterpart. The difference between UFG chromium bronze and its CG counterpart is also significant in terms of corrosion morphology. Though the structure is uniform corrosion, the microstructure is honeycomb-like morphology for CG chromium bronze and the corrosion pit is deeper. The shallower corrosion pits are displayed for UFG chromium bronze and grain drop off in local region.
12
Eric, R. H. "Chromous capacities of ferrochromium and matte smelting slags." Archives of Materials Science and Engineering 2, no. 93 (October 1, 2018): 49–58. http://dx.doi.org/10.5604/01.3001.0012.7354.
Full textAbstract:
Purpose: of this paper is to extend the slag capacity concept to sparingly soluble cationic species encountered for example in matte smelting and ferrochromium processing in terms of chromous capacities. Design/methodology/approach: In this context in order to develop the chromous capacity the experimental data on slag-metal equilibrium for ferrochromium smelting and on chromium distribution between slag and matte phases encountered in sulphide smelting of PGM (Platinum Group Metals) and chromium containing copper nickel concentrates were used. Findings: The calculated chromous capacities were in the 10-8 range for ferrochrome smelting slags and 10-4 range for matte smelting slags. These values indicate the very low and moderate chromous ion dissolving ability of ferrochromium smelting slags and matte smelting slags respectively. Research limitations/implications: Due to highly reducing conditions in ferrochromium smelting and the imposed low oxygen partial pressures in sulphide smelting of chromium and PGM containing concentrates chromium in the slag was assumed to be in its divalent state. The slag-metal/matte reaction for dissolution of chromium into the slag as a cation under reducing conditions -in contrast to reactions for dissolution of species such as sulphur and phosphorus into the slag as anions under oxidizing conditions – required the release of electrons. Thus to maintain charge neutrality the dissolution of chromium from the metal or the matte phases into the slag as Cr2+ ions was accompanied by consumption of these electrons by reduction of Fe2+ ions in the slag into metallic Fe which dissolved in the metal/ matte phase. This was supported by the experimental equilibrium data. Hence the slagmetal/ matte reaction defining the chromous capacity involved both O2- and Fe2+ ions of the slag phase. Moreover for matte smelting the thermodynamic activities of species in the matte phase were assumed to conform to ideal associated solution model due to lack of data. For future work it is advisable to determine such activities. Practical implications: The calculated chromous capacities were in the 10-8 range for ferrochrome smelting slags and 10-4 range for matte smelting slags. The results clearly indicate that in matte smelting lower basicity slags would be preferable to render chromium more soluble in the slag in contrast to ferrochromium smelting where higher basicity slags would be suitable to minimize chromium losses to the slag. Originality/value: This research and hence the paper is probably the first on dissolution of chromium as chromous ion in slags, thus it is novel and original.
13
Jin, Lan Shu, Xue Feng Chu, Guo Lin Lin, and Bo Ying. "Removal of Trivalent Chromium ION in Wastewater by Zeolite 4a." Advanced Materials Research 383-390 (November 2011): 6091–96. http://dx.doi.org/10.4028/www.scientific.net/amr.383-390.6091.
Full textAbstract:
Under the static condition, researching zeolite 4A to the chromium ion's adsorption characteristic, discussing the influence of different adsorption factors. The results indicated that: When the wastewater temperature was 30°C, at pH 3-4,adsorbed 30min,dosing 3g/L of zeolite 4A adsorption chromic wastewater(100mg/L), the chromium ion elimination rate may reached above 99%. At the same time, the zeolite 4A conforms to Langmuir and the Freundlich isotherm to the chromium ion's adsorption, the correlation coefficient respectively was 0.9997 and 0.9753, obtained the zeolite 4A to the chromium ion saturated adsorptive capacity was 50.25mg/L.Obviously, zeolite 4A as a new inorganic ions exchange material for the treatment of chromic wastewater, has the broad prospects for development.
14
Hu, Shaoyan, Deyong Wang, Xianglong Li, Wei Zhao, Tianpeng Qu, and Yun Wang. "Enrichment Characteristics of Cr in Chromium Slag after Pre-Reduction and Melting/Magnetic Separation Treatment." Materials 14, no. 17 (August 30, 2021): 4937. http://dx.doi.org/10.3390/ma14174937.
Full textAbstract:
Concentrating the chromium in chromium slag and improving the chromium–iron ratio is beneficial for the further utilization of chromium slag. In this paper, chromium slag obtained from a chromite lime-free roasting plant was used as the raw material. Pellets made of the chromium slag and pulverized coal were reduced at different pre-reduction temperatures and then separated by a melting separation process or magnetic separation process, respectively. The mass and composition of the metallized pellets before separation, along with the alloy and tail slag after separation, were comprehensively analyzed. The experimental results showed that the output yield of alloy, iron recovery rate, and chromium content in the alloy were all higher when using melting separation than when using magnetic separation, because of the further reduction during the melting stage. More importantly, a relatively low pre-reduction temperature and selection of magnetic separation process were found to be more beneficial for chromium enrichment in slag; the highest chromium–iron ratio in tail slag can reach 2.88.
15
Fébel, Hedvig, B. Szegedi, and Szilvia Huszár. "Absorption of inorganic, trivalent and hexavalent chromium following oral and intrajejunal doses in rats." Acta Veterinaria Hungarica 49, no. 2 (April 2001): 203–9. http://dx.doi.org/10.1556/004.49.2001.2.10.
Full textAbstract:
The intestinal absorption of trivalent and hexavalent chromium (Cr) given orally (experiment I) or infused in the intestine (experiment II) was investigated in rats. The nonabsorbable form of chromium (51Cr2O3) and water-soluble and more absorbable Na251CrO4 (the hexavalent form of Cr) were compared. Total retention of chromium given orally ranged around 15 percent of the dose, regardless of the chromium compounds applied. The absorption rate of chromic oxide, which is considered a nonabsorbable compound, was 14.4 as a percentage of chromium intake. This result indicates that some loss of chromium has to be taken into account in metabolic trials made by the indicator method. In isolated rat intestine, from the injected Cr 2.5% of chromic oxide and 43.2% of sodium chromate were absorbed during an hour (experiment II). The absorbed chromium was transferred to the liver where the liver tissue retained 10.9% of chromic oxide and 51.1% of sodium chromate. Radioactivity of v. cava caudalis following intestinal injection of Na2CrO4 was thirtyfold greater than after Na2CrO4 dosing. This phenomenon can be explained by the lower blood clearance of chromate. Different absorption rate of chromate depending on the route of administration could be due to the fact that the hexavalent form given orally was reduced to Cr3+ in the acidic environment of the stomach. When Na2CrO4 was infused directly in the intestine of rats, such reduction could not occur. This means that the acidic gastric juice might play a role in inhibiting the intestinal absorption of Na2CrO4 when this compound is given orally.
16
Ge, X., S. Jin, M. Zhang, X. Wang, and S. Seetharaman. "Synthesis of chromium and ferrochromium alloy in molten salts by the electro-reduction method." Journal of Mining and Metallurgy, Section B: Metallurgy 51, no. 2 (2015): 185–91. http://dx.doi.org/10.2298/jmmb141222022g.
Full textAbstract:
In this work, we successfully applied the Fray-Farthing-Chen Cambridge electro-reduction process on the preparation of chromium from chromium oxide, and for the first time, the synthesis of ferrochromium alloy from chromium oxide and iron oxide mixture and the chromite ore in molten calcium chloride. The present work systematically investigated the influences of sintered temperature of the solid precursor, electrochemical potential, electrolysis temperature and time on the products by using a set of advanced characterization techniques, including XRD and SEM/EDS analyses. In particular, our results show that this process is energy-friendly and technically-feasible for the direct extraction of ferrochromium alloy from chromite ore. Our findings thus provide useful insights for designing a novel green process to produce ferrochromium alloy from low-grade chromite ore or stainless steel slag.
17
Dyussenova, S., B. Kenzhaliyev, R. Abdulvaliyev, and S. Gladyshev. "The method of processing technogenic tailings of chromium." Journal of Mining and Metallurgy A: Mining 56, no. 1 (2020): 15–22. http://dx.doi.org/10.5937/jmma2001015d.
Full textAbstract:
Taking into account the existing demand for chromium concentrates, the extraction of chromium from technogenic formations of sludge storages of the tailings of chromium ore beneficiation is an important practical task. The comprehensive utilization of beneficiation sludge will increase the profitability of production and solve the environmental problems of the region. The importance of solving the problem of involving in processing tailings is connected not only with the environment but also with the need to increase the production of chromium. Modern gravity enrichment technologies make it possible to efficiently produce chromium concentrates from large and medium fractions of chromite-containing ores, while finely divided sludge is practically not extracted due to the difficulty of separating complex minerals into concentrates and waste rock. This paper presents the results of studies on the gravity processing of tailings. The technology includes the enrichment of the fine fraction-0.2+0 mm of tailings of the dressing plant of chromite-containing ores by gravity methods using a KNELSON centrifugal separator. In technology, the efficiency of the operation of gravity enrichment is provided by the preliminary activation of the fine fraction in a solution of sodium bicarbonate (NaHCO3). With gravitational enrichment, the total chromite concentrate was obtained containing 51.3% Cr2O3. The output of concentrate was 41.7%. The extraction of Cr2O3 in the concentrate was 68.1%.
18
Turakulov, Bakhriddin, Kurmanbek Zhantasov, Alexandr Kolesnikov, Bakyt Smailov, and Yury Liseitsev. "Research on the Production of Pigments Based on Composite Pellets in the Recycling of Industrial Waste." Journal of Composites Science 7, no. 7 (July 13, 2023): 289. http://dx.doi.org/10.3390/jcs7070289.
Full textAbstract:
This article presents the complex processing of low-grade and substandard chromium ores, as well as sludge tailings, with the production of composite chromium-containing materials and pigments, while improving environmental performance in the Republic of Kazakhstan through the utilization and processing of technogenic raw materials. In this work, to study the physicochemical properties of the starting materials, modern analytical, thermodynamic, chemical, granulometric, as well as computational, mathematical, laboratory, and experimental methods were used. In particular, studies of a method for producing composite pellets for chromite pigments based on industrial technogenic waste of the Republic of Kazakhstan are presented. Based on the results of the experimental studies, composite pellets were obtained, having a compressive strength of 150–220 kg/pellet and containing 49.7% of chromium oxide and 0.5–1.0% of carbon in its composition. The resulting chromite pigment based on the composite pellets is a modification of chromium oxohydroxide with the formula γ-CrOOH. The density of the resulting pigment is 3.4 kg/m3. The chromite pigment based on the composite pellets is recommended for use in various coloring compositions, including using it for printing on cotton and mixed fabrics intended for sewing outerwear.
19
Zhang, Ya Ni, Chang Zheng Xu, Mao Sheng Zheng, and Jie Wu Zhu. "Effect of ECAP on the Electrochemical Behavior of Chromium Bronze." Advanced Materials Research 239-242 (May 2011): 98–101. http://dx.doi.org/10.4028/www.scientific.net/amr.239-242.98.
Full textAbstract:
The effect of equal channel angular pressing (ECAP) process on the electrochemical behavior of chromium bronze in NaCl solution was investigated by three-electrode cell setup. The result shows the difference of electrochemical behavior between X plane and Y plane is still exist, and even in the unodd number passes for “route C” of ECAP process. ECAP process don’t change the corrosion nature of chromiun bronze, but the corrosion potential of 12 passes ultra-fine grain (UFG) chromium bronze is a little more positive than that of 0 pass chromium bronze. For better understanding the effect of ECAP on the electrochemical behavior of chromium bronze, we chose the cold-rolled materials with the same composition as reference materials. The result shows that ECAP process is more benefical to electrochemical behavior of chromium bronze than cold-rolled process. On the other hand, the result of EIS also shows that ECAP process is more benefical to form compacted corrosion layers on the surface of specimens.
20
Galerie, Alain, Jean Pierre Petit, Yves Wouters, Julie Mougin, Anusara Srisrual, and 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.
Full textAbstract:
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.
21
Tastanov, Ye A., N. Kh Serzhanova, N. M. K. Sadykov, Zh A. Yerzhanova, and A. Ye Tastanova. "Physical and chemical studies of finely-dispersed slurry tailings of the Donskoy Ore Mining and Processing Plant (DMPP) for chemical beneficiation to produce chromium concentrate." Engineering Journal of Satbayev University 145, no. 2 (2023): 5–12. http://dx.doi.org/10.51301/ejsu.2023.i2.01.
Full textAbstract:
During the processing of chromium ores, chromite concentrate is obtained for the production of ferrochrome, and waste is also collected - tailings beneficiation. Fragment and sludge tailings depending on the beneficiation technology. Finely dispersed sludge tailings of the Donskoy MPP of Kazchrome JSC are stored at the Dubersay and Akzhar tailings, which are man-made deposits (MMD) or man-made mineral formations (MMF). To develop a technology for processing sludge tailings, which contain up to 30% chromium oxide, their physical and chemical studies were carried out. According to the chemical analysis of sludge tailings, it follows that research should be directed to the removal of magnesium and silicon oxides, thereby increasing the content of chromium oxide to a standard chromium concentrate. A very thin dissemination of chromite with minerals of host rocks necessitates additional grinding of intermediate products, which are intergrowths of chromite with waste rock. According to the results of fractional analysis and IR spectroscopy, the content of a large number of flocculants in the studied sludge tailings and a large number of particles with a particle size of less than 20 μm, which, in heavy liquid solutions, due to its small size, is in suspension and does not stratify, was revealed. According to the granulometric composition, it was determined that the sludge minus 0.071 mm must also be classified into 0.04 and 0.02 mm and enriched each class separately. It has been established that in order to obtain high technological performance, the traditional gravitational beneficiation scheme used at the DMPP is technologically cumbersome, because includes operations of flocculant disintegration, classification, grinding, beneficiation on concentration tables of each size class, regrinding of intermediate products. The results of the physicochemical study of chromium sludge tailings showed the need for a combined beneficiation scheme, including chemical enrichment with finishing of chromium concentrate by gravity beneficiation.
22
Escudero-Castejon, Lidia, Sergio Sanchez-Segado, Stephen Parirenyatwa, and 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, no. 4 (December 1, 2016): 215–25. http://dx.doi.org/10.1515/jmsp-2016-0023.
Full textAbstract:
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.
23
Ledoux, Xiaver, Michel Vilasi, Stéphane Mathieu, Pierre Jean Pantiex, Pascal Del-Gallo, and Marc Wanger. "Development of Chromium and Aluminum Coatings on Superalloys by Pack-Cementation Technique." Advanced Materials Research 278 (July 2011): 491–96. http://dx.doi.org/10.4028/www.scientific.net/amr.278.491.
Full textAbstract:
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.
24
Fomichev, V. T., A. V. Savchenko, and G. P. Gubarevich. "Specific Morphological Features of the Surface of Chromium Coatings Obtained in Electrolytes with Organic Additives." Materials Science Forum 1083 (April 6, 2023): 147–52. http://dx.doi.org/10.4028/p-kn0n0v.
Full textAbstract:
At the present time, the electrodeposition of chromium metal coatings of sufficient thickness and quality is possible only from chromium plating electrolytes containing chromic acid. The authors investigated the effect of the composition of chromium plating electrolyte on the quality of the resulting metal coating. It has been demonstrated that the introduction of organic additives, of gallic acid in particular, leads to significant changes in the surface of the metal deposit and to a decrease in its hardness. Assumptions have been made about the influence of organic additives on the metal deposition process. The experimental data on the content of gases in the chromium deposits obtained from electrolytes with gallic acid additive and without it have been presented.
25
Ozdilek, Zehra. "Teaching the properties of chromium's oxidation states with a case study method." Chemistry Education Research and Practice 16, no. 1 (2015): 39–52. http://dx.doi.org/10.1039/c4rp00176a.
Full textAbstract:
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.
26
Islam, Md Saiful, Md Jahid Hasan, Promita Poroma, and Sraboni Akter. "A review on the environment friendly electroplating of Cr (III) & Cr (VI)." Journal of Science and Engineering Papers 01, no. 01 (January 18, 2024): 31–39. http://dx.doi.org/10.62275/josep.24.1000006.
Full textAbstract:
Chromium plating process is the most effective way of protecting the base material against hostile environment or improving surface properties of base material. There are several problems with traditional chrome plating. Traditional process uses toxic acid baths and may cause various health conditions. The baths employed contain chromic acid in which the chromium is in the hexavalent state. Hexavalent chromium has been proved to have toxic, mutagenic and cancerogenic effects for human health. As a result, In Europe, the implementation of the reach initiative will increase fees on companies still using Cr (VI) in 2017 and will require action plans to phase out Cr (VI) in the future. This has left the plating industry in a very delicate position with dark future prospects unless new solutions that are both effective and environmentally friendly are discovered. Superchrome Physical Vapor Deposition coating ahead of looming industry regulatory actions that will drive towards the removal of hazardous hexavalent chromium compounds. These new sputtered chromium coatings do not require a protective paint top coat to pass exterior automotive trim specifications. Visually the chromium coatings match those of electroplated decorative chromium in color and appearance.
27
Toyoshima, Akio, Takashi Kikuchi, Hirokazu Tanaka, Kazuhiko Mase, and Kenta Amemiya. "In situremoval of carbon contamination from a chromium-coated mirror: ideal optics to suppress higher-order harmonics in the carbonK-edge region." Journal of Synchrotron Radiation 22, no. 6 (September 26, 2015): 1359–63. http://dx.doi.org/10.1107/s1600577515015040.
Full textAbstract:
Carbon-free chromium-coated optics are ideal in the carbonK-edge region (280–330 eV) because the reflectivity of first-order light is larger than that of gold-coated optics while the second-order harmonics (560–660 eV) are significantly suppressed by chromiumL-edge and oxygenK-edge absorption. Here, chromium-, gold- and nickel-coated mirrors have been adopted in the vacuum ultraviolet and soft X-ray branch beamline BL-13B at the Photon Factory in Tsukuba, Japan. Carbon contamination on the chromium-coated mirror was almost completely removed by exposure to oxygen at a pressure of 8 × 10−2 Pa for 1 h under irradiation of non-monochromated synchrotron radiation. The pressure in the chamber recovered to the order of 10−7 Pa within a few hours. The reflectivity of the chromium-coated mirror of the second-order harmonics in the carbonK-edge region (560–660 eV) was found to be a factor of 0.1–0.48 smaller than that of the gold-coated mirror.
28
Choe, Yeong-Ju, Kyoung-Jin Lee, and Hae-Jin Hwang. "Cr Poisoning On Nd2Ni0.95Cu0.05O4+δ Cathode for Solid Oxide Fuel Cells." Archives of Metallurgy and Materials 61, no. 2 (June 1, 2016): 629–34. http://dx.doi.org/10.1515/amm-2016-0107.
Full textAbstract:
Abstract In this study, Nd2Ni1-xCuxO4+δ (x=0, 0.05, 0.1, and 0.2) layered perovskite powders were synthesized by the glycine nitrate process (GNP) and the chromium poisoning effect on the electrochemical performance of the Nd2Ni0.95Cu0.05O4+δ and La0.6Sr0.4Co0.2Fe0.8O3-δ cathodes were investigated. In the case of the LSCF cathode, the strontium chromite phase formed after the exposure of the gaseous chromium species, while there was no additional phase in the Nd2Ni0.95Cu0.05O4+δ cathode. The area specific resistance (ASR) of the Nd2Ni0.95Cu0.05O4+δ cathode did not change significantly after the exposure of the gaseous chromium species at 800°C.
29
Ardashev, D. V., L. V. Shipulin, and A. S. Degtyareva-Kashutina. "Aspects of Applying Hard Chromium Coatings on the Inner Surfaces of Components for Hydraulic Drives with Hydrostatic Guideways." Solid State Phenomena 316 (April 2021): 827–32. http://dx.doi.org/10.4028/www.scientific.net/ssp.316.827.
Full textAbstract:
We considered the processes of chromium plating the inner surfaces of the components of cylinders with hydrostatic guideways. We demonstrated the various aspects of the chromium plating process – the limitations placed on the machinery depending on the dimensions of the parts to be plated and the unevenness of the deposition rate of chromium along the length of the part. We developed a diagram of an installation for the application of a hard chromium coating on inner surfaces, which includes a cathode, an anode, a tank, and a pipeline. The distinctive features of the installation are the method of supplying the electrolyte at an angle to the horizontal, which allows us to supply the electrolyte through a turbulent flow swirling along a helical path, and the use of a chromium-plated installation casing. We studied various modes for applying a hard chromium coating on the inner surfaces of a hydraulic cylinder. As a result, we determined the optimal composition of the chromium electrolyte – the ratio of chromic anhydride and sulfuric acid – which is 10:1, respectively, and experimentally selected deposition modes. Chromium coatings obtained through the use of the concentrated electrolyte, which we developed, and the chromium plating method have 5...20% greater hardness and a 10...30-times reduction in porosity with the formation of a shiny, lumpy sludge, which corresponds to corrosion-resistant and wear-resistant coatings needed to manufacture hydraulic drives with highly efficient hydrostatic guideways.
30
Zhao, Yuhao, Conrad Kumul, Tiangang Wang, Nathan Mosusu, Zhongyou Yao, Yiping Zhu, Bimin Zhang, and Xueqiu Wang. "National-Scale Geochemical Baseline and Anomalies of Chromium in Papua New Guinea." Minerals 13, no. 2 (January 31, 2023): 205. http://dx.doi.org/10.3390/min13020205.
Full textAbstract:
Papua New Guinea (PNG) is located at the convergence edge of the Pacific Plate and the Indo-Australian Plate, consisting of three units. There are three chromium mineralization types in PNG. Based on national-scale geochemical mapping in PNG during 2015–2018, 1399 samples of stream sediments were collected from Highland Region, Papua Peninsula, and New Guinea Islands. This paper preliminarily studied chromium’s geochemical background, spatial distribution characteristics, and geochemical anomalies. The chromium concentration ranged from 3 ppm to 74,600 ppm, with a median value of 145 ppm, which was higher than the upper crustal abundance of chromium and the chromium geochemical baseline of Europe, Australia, North America, and China. In terms of stream sediment samples in different tectonic units, as mafic–ultramafic magmatic rocks are widely developed, the median chromium values of the New Guinea Orogen, including the Papuan Fold Belt, the New Guinea Thrust Belt, the Finisterre Terrane, the Aure Fold Belt, the Eastern Fold Belt, and the Eastern Papuan Composite Terrane, were higher than the value of the Melanesian Arc. The ophiolitic complexes, such as the April ophiolite, the Marum ophiolite, and the Papua ultramafic belt, significantly correlated with the higher chromium concentration. Eleven chromium high anomalies with mineralization potential were delineated, including three laterite and podiform prospecting areas and eight placer prospecting areas. Based on the chromium–nickel integrated anomaly map, comprehensive exploration and exploitation of nickel and chromium can be carried out in 1 and 11 high anomaly areas related to lateritic mineralization.
31
Cameron, T. Stanley, Jason AC Clyburne, Pramod K. Dubey, J. Stuart Grossert, K. Ramaiah, J. Ramanatham, and 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, no. 6 (June 1, 2003): 612–19. http://dx.doi.org/10.1139/v03-042.
Full textAbstract:
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.
32
Berthod, Patrice, and 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.
Full textAbstract:
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.
33
CHOI, Y., N. I. CHO, and J. I. CHOE. "QUANTITATIVE STUDY OF SURFACE MORPHOLOGY BY ATOMIC FORCE MICROSCOPY." International Journal of Modern Physics B 16, no. 28n29 (November 20, 2002): 4395–400. http://dx.doi.org/10.1142/s0217979202015480.
Full textAbstract:
Atomic force microscopy was applied to study the formation and growth mechanism of thin multilayers of chromium-molybdenum and chrome prepared by electro-pulse plating, respectively. The chromium-molybdenum and chrome layers were prepared using direct current density of 1.6 mA.mm -2 and pulse currents with on-off time from 5 to 2000 ms in the bath containing 300g l-1 of chromic acid and 75g l-1 ammonium molybdate, and 250g l-1 of chromic acid and 5g l-1 of sulfuric acid, respectively. The higher current density enhanced nucleation rate which resulted in refining grain size. The micro-hardness of the pulse plated chrome and chromium-molybdenum alloy layers increased with the duration of on-off time and pulse current density. The average surface roughness of chrome layer is increased with increasing on/off time ratio for a given peak current density and voltage because the growth and dissolution mainly occurs during on-time and off-time, respectively. However, the average surface roughness of chromium-molybdenum alloy layer is decreased with increasing on/off time ratio for a given peak current density and voltage because the alloying element in the layer.
34
von Burg, R., and D. Liu. "Chromium and hexavalent chromium." Journal of Applied Toxicology 13, no. 3 (May 1993): 225–30. http://dx.doi.org/10.1002/jat.2550130315.
Full text
35
Eliseeva, Olga V. "Application of atomic absorption spectroscopy for the analysis of chemical composition of Brassica rapa." Butlerov Communications 61, no. 2 (February 29, 2020): 46–50. http://dx.doi.org/10.37952/roi-jbc-01/20-61-2-46.
Full textAbstract:
This paper presents the study of the chemical composition of Petrovskaya variety of turnip after the non-root treatment of vegetating plants with the solution of trivalent chromium. The treatment has been performed with the solutions of chromic potassium sulphate with chromium concentrations of 0.002% and 0.005%. The experiment has been conducted according to the following scheme: 1. NPK (background) – control version; 2. NPK + HO Cr 0.002%; 3. NPK + HO Cr 0.005%. Nitroammophoska was used as the background macro fertiliser during the sowing at the rate of 30 g/m2. In the control versions plants have been treated with the distilled water. The content of chromium in root vegetables has been assessed using the method of atomic absorption spectroscopy. It is shown that after the treatment with the solution of chromic potassium sulphate the average content of chromium in root vegetables increased by 31.3% in NPK + Cr 0.002% version and by 55.6% in NPK + Cr 0.005% version in comparison with the control version. At the chromium concentration of 0.002% the content of dry matter in turnip remained at the level of control version, the content of dry soluble matters and ascorbic acid decreased down to 5.9% and 28.60 mg/100 g, the level of nitrates in root vegetables increased up to 286.0 mg/kg of wet mass. At the chromium concentration of 0.005% the content of dry matter in turnip decreased down to 10.4%, the content of dry soluble matters increased up to 7.3%, the content of ascorbic acid and nitrates decreased down to 27.81 mg/100 g and 210.2 mg/kg of wet mass, respectively.
36
Gossé, Stéphane, Thierry Alpettaz, Fabien Rouillard, Sylvie Chatain, Christine Guéneau, and Céline Cabet. "Direct Measurements of the Chromium Activity in Complex Nickel Base Alloys by High Temperature Mass Spectrometry." Materials Science Forum 595-598 (September 2008): 975–85. http://dx.doi.org/10.4028/www.scientific.net/msf.595-598.975.
Full textAbstract:
Chromium rich, nickel based alloys Haynes 230 and Inconel 617 are candidate materials for the primary circuit and intermediate heat exchangers (IHX) of (Very)-High Temperature Reactors. The corrosion resistance of these alloys is strongly related to the reactivity of chromium in the reactor specific environment (high temperature, impure helium). At intermediate temperature – 900°C for Haynes 230 and 850°C for Inconel 617 – the alloys under investigation are likely to develop a chromium-rich surface oxide scale. This layer protects from the exchanges with the surrounding medium and thus prevents against intensive corrosion processes. However at higher temperatures, it was shown that the surface chromia can be reduced by reaction with the carbon from the alloy [1] and the bare material can quickly corrode. Chromium appears to be a key element in this surface scale reactivity. Then, quantitative assessment of the surface requires an accurate knowledge of the chromium activity in the temperature range close to the operating conditions (T ≈ 1273 K). High temperature mass spectrometry (HTMS) coupled to multiple effusion Knudsen cells was successfully used to measure the chromium activity in Inconel 617 and Haynes 230 in the 1423- 1548 K temperature range. Appropriate adjustments of the experimental parameters and in-situ calibration toward pure chromium allow to reach accuracy better than ± 5%. For both alloys, the chromium activities are determined. Our experimental results on Inconel 617 are in disagreement with the data published by Hilpert [2]. Possible explanations for the significant discrepancy are discussed.
37
Chen, Zhe, Ying Chen, Jing Liang, Zhiyu Sun, Haoren Zhao, and Yi Huang. "The Release and Migration of Cr in the Soil under Alternating Wet–Dry Conditions." Toxics 12, no. 2 (February 8, 2024): 140. http://dx.doi.org/10.3390/toxics12020140.
Full textAbstract:
In recent decades, chromium contamination in soil has emerged as a serious environmental issue, demanding an exploration of chromium’s behavioral patterns in different soil conditions. This study aims to simulate the release, migration, and environmental impact of chromium (Cr) in contaminated soils under natural rainfall conditions (wet–dry cycles). Clean soils sourced from Panzhihua were used to cultivate chromium-containing soils. Simulated rainfall, prepared in the laboratory, was applied to the cultivated chromium-containing soils in indoor simulated leaching experiments. The experiments simulated three years of rainfall in Panzhihua. The results indicate that soils with higher initial Cr contents result in higher Cr concentrations in the leachate, but all soils exhibit a low cumulative Cr release. The leachate shows similar patterns in total organic carbon (TOC), pH, electrical conductivity, and Cr content changes. An analysis of the speciation of Cr in the soil after leaching reveals a significant decrease in the exchangeable fraction for each Cr species, while the residual and oxidizable Cr fractions exhibit notable increases. The wet–dry cycle has the following effects on the soil: it induces internal reduction reactions in the soil, leading to the reduction of Cr(VI) to Cr(III); it alters the binding of Cr ions to the soil, affecting the migration of chromium; and it involves microorganisms in chemical processes that consume organic matter in the soil. After three years of rainwater leaching, chromium-containing soils released a relatively low cumulative amount of total chromium, resulting in a reduced potential risk of groundwater system contamination. Most of the chromium in the chromium-containing soil is fixed within the soil, leading to less biotoxicity.
38
Demir, Orhan, and Rauf Hurman Eric. "Rate and Mechanism of Reduction-Dissolution of Chromite in Liquid Slags." High Temperature Materials and Processes 32, no. 3 (June 14, 2013): 255–63. http://dx.doi.org/10.1515/htmp-2012-0133.
Full textAbstract:
AbstractThe dissolution of chromite from the Bushveld Complex of South Africa in liquid slags was studied in the temperature range 1550° to 1665°C under argon gas. The slag compositions were similar to those of ferrochromium production and stainless steel making. Empirical relations between the slag composition and the dissolution of chromite were established through the use of a statistical model. The dissolution process was investigated by using the rotating cylinder technique and measured by the chemical analysis of the samples taken from the melt and the SEM-EDAX analysis of the reacted chromite cylinder samples. The chromite grains were depleted in iron and chromium as the dissolution progressed, leaving behind an alumina and magnesia rich spinel. The experimental data was evaluated by using kinetic models and mass transfer coefficients of chromium, iron and oxygen ions through the phase boundary between the solid chromite cylinder and the liquid slag were determined.The dissolution of chromite in liquid slags increases with increasing stirring rate. SEM-EDAX studies on the reacted chromite cylinders showed that coring took place within the chromite grains subjected to dissolution for sufficient length of time. Chromium and iron concentrations in the chromite were decreasing from the centre towards the surface of the grains while aluminum and magnesium contents were increasing at the edges compared to the centre of the chromite grains. Furthermore, the slag rich in alumina and magnesia diffuses in bulk into the chromite with a net result of increase in the concentration of these elements.The rate of dissolution of chromite in liquid slags was found to be controlled by the mass transfer of oxygen ions (O2−) through the liquid phase boundary between the solid chromite and the liquid slag. The activation energy for the mass transfer of O2− ions was calculated as 30.61 kCal/mol (128.07 kJ/mol).
39
Tanahashi, N., A. Takeuchi, and K. Tanaka. "Metal Recovery From the Waste Magnesia-Chromia Bricks With Arc Plasmas." Journal of Energy Resources Technology 123, no. 1 (October 30, 2000): 76–80. http://dx.doi.org/10.1115/1.1346681.
Full textAbstract:
A process has been developed to detoxify the waste magnesia-chromia bricks containing sexivalent chromium and recover valuable materials with arc plasma treatment. Especially magnesium and chromium, which are the major compounds of the waste bricks, could be separately recovered by carbothermic reduction with addition of iron. From the viewpoint of environmental protection and saving resources, such recovery processes are expected to be commercialized.
40
Dulińska, D., W. Pawlak, and Z. Grzesik. "The Prospects In Designing New Generation Of High Temperature Coatings In Automobile Engines." Archives of Metallurgy and Materials 60, no. 2 (June 1, 2015): 903–7. http://dx.doi.org/10.1515/amm-2015-0227.
Full textAbstract:
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.
41
Fomichev, V. T., A. V. Savchenko, and G. P. Gubarevich. "Functional Galvanic Coatings of the Cr-Zn System." Materials Science Forum 945 (February 2019): 688–94. http://dx.doi.org/10.4028/www.scientific.net/msf.945.688.
Full textAbstract:
The authors have studied the influence of the electric current density, temperature, electrolyte composition on the properties of electroplating Chromium-Zinc deposits. The dependence of the maximum yield of metal on the physico-chemical characteristics of the solutions for electroplating of Chromium and Cr-Zn alloy has been shown. Chromium-Zinc coatings have been obtained from electrolytes based on chromic acid in the presence of organic additive (4-methylaminophenol). Abrupt nonlinear changes in density, viscosity, surface tension, specific electrical conductivity due to structural transformations in electrolytes are observed at the concentration of zinc sulphate of 4070 gramm / litr (further in the text - g/l), and the organic additive of 2-5 g/l. The obtained model has been applied to predict the optimal electrolyte compositions for the processes of Cr-Zn alloy formation, which will allow reducing the research efforts concerning the electrochemical studies of the given process when chromic acid solutions are used. The coatings exhibit high hardness, corrosion resistance, wear resistance, low internal stresses.
42
Atasoy, Ahmet, and F. R. Sale. "An Investigation on the Solid State Reduction of Chromite Concentrate." Solid State Phenomena 147-149 (January 2009): 752–57. http://dx.doi.org/10.4028/www.scientific.net/ssp.147-149.752.
Full textAbstract:
In this article, Turkish chromite concentrate was reduced with metallurgical coke at temperature between 1000-1500 °C with variables reducing times. The reduction mechanism and the microstructure of the reduced chromite were investigated. There were closer relationships between the reduction of chromite and the sample morphology, such as, the surface area and the porosities and cracks of the particle have positive effect on the metallization of iron and chromium oxides. The reduction of the iron chromite spinel started at 1000 °C, but picrochromite started to reduce at temperature around 1300 °C. At lower temperature, the formation of iron carbide phases was affected on the formation of ferro alloy and accelerates the reduction of chromium. The formation of carbon monoxide was also affected on the reduction of chromite spinel, especially around imperfections of grain where porosity, cracks and fractures act as diffusion channel for the reducing gas. For the charecterisation of the reaction products, X-ray diffraction techniques, SEM and EDAX were used.
43
Zakharov, L. S., A. R. Gavrik, and V. N. Lipodaev. "Electrodes for welding of dissimilar chromium martensitic and chromium-nickel austenitic steels." Paton Welding Journal 2014, no. 6 (June 28, 2014): 139–42. http://dx.doi.org/10.15407/tpwj2014.06.30.
Full text
44
Mukashev, N. Zh, N. Y. Kosdauletov, and B. T. Suleimen. "Comparison of Iron and Chromium Reduction from Chrome Ore Concentrates by Solid Carbon and Carbon Monoxide." Solid State Phenomena 299 (January 2020): 1152–57. http://dx.doi.org/10.4028/www.scientific.net/ssp.299.1152.
Full textAbstract:
The possibility of reduction of chromium and iron from complex oxides by gaseous carbon monoxide and solid carbon was investigated. The chromium ore concentrates of Kempirsai and Aganozero deposits used in present study had different ratio of iron and chromium content. The Reduction in CO gas atmosphere did not result in reduction of chromium and iron from spinels; however, it resulted in reduction of fines from the drying apparatus, where the particles of coke presented along with the particles of the Kempersai chromite. At the same time, iron and nickel were reduced from the silicates of the gangue minerals. In the samples mixed with solid carbon a continuous layer of carbides formed on the surface of the spinel grains. The formation of a continuous shell retarded and practically stopped the reduction process. The further development of reduction was possible after destruction of the shell that occurred as a result of smelting of the carbides and silicides mixture that constitute the shell.
45
Gidikova, N., M. Sulowski, V. Petkov, R. Valov, and G. Cempura. "Composite Coatings of Chromium and Nanodiamond Particles on Steel." Archives of Metallurgy and Materials 62, no. 4 (December 1, 2017): 2421–24. http://dx.doi.org/10.1515/amm-2017-0356.
Full textAbstract:
AbstractChrome plating is used to improve the properties of metal surfaces like hardness, corrosion resistance and wear resistance in machine building. To further improve these properties, an electrodeposited chromium coating on steel, modified with nanodiamond particles is proposed. The nanodiamond particles (average size 4 nm measured by TEM) are produced by detonation synthesis (NDDS). The composite coating (Cr+NDDS) has an increased thickness, about two times greater microhardness and finer micro-structure compared to that of unmodified chromium coating obtained under the same galvanization conditions. In the microstructure of specimen obtained from chrome electrolyte with concentration of NDDS 25 g/l or more, “minisections” with chromium shell were found. They were identified by metallographic microscope and X-ray analyser on etched section of chromium plated sample. The object of further research is the dependence of the presence of NDDS in the composite coating from the nanodiamond particles concentration in the chroming electrolyte.
46
Paustenbach, Dennis J., Deborah M. Meyer, Patrick J. Sheehan, and Virginia Lau. "An Assessment and Quantitative Uncertainty Analysis of the Health Risks to Workers Exposed to Chromium Contaminated Soils." Toxicology and Industrial Health 7, no. 3 (May 1991): 159–96. http://dx.doi.org/10.1177/074823379100700304.
Full textAbstract:
Paustenbach, Dennis J., Deborah M. Meyer, Patrick J. Shee han, and Virginia Lau (1991). An assessment and quantitative uncertainty analysis of the health risks to workers exposed to chromium contaminated soils. Toxicol. Industrial Health. Millions of tons of chromite-ore processing residue have been used as fill in various locations in Northern New Jersey and else where in the United States. The primary toxicants in the residue are trivalent chromium [ Cr(III)] and hexavalent chromium [ Cr(VI)]. The hazard posed by Cr(III) is negligible due to its low acute and chronic toxicity. In contrast, Cr(VI) is considered a inhalation human carcinogen at high concentrations. Approxi mately 40 commercial and industrial properties in Northern New Jersey have been identified as containing chromite ore processing residue in the soil. One site, a partially-paved trucking terminal, was evaluated in this assessment. The arithmetic mean and geo metric mean concentrations of total chromium in soil were 977 and 359 mg/kg, respectively. The data were log-normal distrib uted. The arithmetic mean and geometric mean concentrations of Cr(VI) in surface soil were 37.6 and 3.1 mg/kg, respectively. The data could not be fit to a standard distribution, likely due to the large number of samples with concentrations below the method detection limit (65%). Dose was calculated for each exposure route using a Monte Carlo statistical simulation.
47
Moffat, T. "Electrochemistry of Chromium, chromium-boron and chromium phosphorus alloys." Solid State Ionics 26, no. 2 (March 1988): 167. http://dx.doi.org/10.1016/0167-2738(88)90143-9.
Full text
48
Wang, Hongyan, Zhonghua Sun, Yaoming Xie, R. Bruce King, and Henry F. Schaefer. "Chromium-Chromium Bonding in Binuclear Azulene Chromium Carbonyl Complexes." European Journal of Inorganic Chemistry 2010, no. 32 (October 5, 2010): 5161–73. http://dx.doi.org/10.1002/ejic.201000737.
Full text
49
Liu, Cheng Jun, Jie Qi, and Mao Fa Jiang. "Experimental Study on Sulfuric Acid Leaching Behavior of Chromite with Different Temperature." Advanced Materials Research 361-363 (October 2011): 628–31. http://dx.doi.org/10.4028/www.scientific.net/amr.361-363.628.
Full textAbstract:
Utilizing Pakistan chromite as raw material, the rapid leaching of chromium and iron could be realized by the sulfuric acid leaching process on the condition of atmospheric pressure and the addition of oxidant A. And the leaching rate of chromium and iron would be 98.5% and 71.9%, respectively. The sulfuric acid leaching processes with different temperature were systematically studied by chemical analysis and phase analysis. The results showed that, with the increase of reaction temperature, the leaching rate of chromium would increase gradually, but the leaching rate of iron increased at first and then decreases and reached its maximum at 140°C. When the temperature > 160°C, the phases of the leaching residue were magnesium iron silicate and a few of silica, no chromohercynite, chrompicotite and magnesioferrite existed in the chromite. The leaching solution of sulfuric acid leaching process could be used for preparing the basic chrome sulfate, and there is no Cr6+ in the leaching residue and solution. The results would provide theoretical guidance for solving environmental pollution problem of Cr6+ in traditional chromate production process.
50
Susaj, Elizabeta, Enkelejda Kucaj, Erald Laçi, and Lush Susaj. "Environmental Impacts Assessment of Chromium Minings in Bulqiza Area, Albania." European Journal of Interdisciplinary Studies 3, no. 4 (October 6, 2017): 35. http://dx.doi.org/10.26417/ejis.v3i4.p35-41.
Full textAbstract:
Bulqiza District is the largest chromium source, ranked fourth in the world for chrome reserves. It lays in the north-eastern part of Albania, 330-1800 m a.s.l, with 728 km² area, between 41o30’43.1N and 20o14’56.21E. There are 136 entities with chromium extraction activity and around the city of Bulqiza (2.6 km² and 13000 inhabitants), there are 33 entities. The aim of the study was the identification of the environmental state and environmental impact assessment of chromium extraction (chromite mining) and giving recommendations to minimize the negative effects of this activity. Field observations, questionnaires, chemical analysis of soil and water, meetings and interviews with central and local institutions as well as with residents were used for the realization of the study. The obtained results showed that chromium extraction causes numerous irreversible degradation of the environment in the Bulqiza area, such as the destruction of surface land layers and erosion, destruction of flora and fauna, soil and water pollution, health problems, unsustainable use and reduction of chromium reserves, etc. The inert waste that emerges after the chromium partition is discharged to the earth surface without any regularity, covering the surface of the soil and flora, leading to irreversible degradation of the environment. Most of the mining entities do not respect the contracts and environmental permit issued by the Ministry of Energy and Industry (MEI).