Papers by Keyword: Chromium

Abstract: This work described the technology of boronizing of titanium Grade2 from the generation of the gas phase directly in a sealed container during the decomposition reactions of the powder saturating medium. With such an implementation of the process in a closed volume, waste gas neutralization devices are not required, since the generation and decomposition of active saturating gases occurs in a closed volume. At saturation of titanium from the gas mixture, titanium borides, titanium nitrides, as well as titanium and chromium carbides can be produced in the coating. The microhardness of the coating is 2800–3200 HV0.1. The thickness of the diffusion coatings in this case can be up to75 microns. It is indicated that diffusion coatings on titanium by this technology should not exceed a thickness of more than 100 microns, and if the thickness of the diffusion coating exceeds 100 microns, the risk of chipping will increase.

Abstract: In this study, microwave irradiation technology was used for the calcification roasting followed by sulfuric acid leaching process. The effect of roasting temperature, m (CaO)/m (V₂O₅), and roasting time on the leaching ratio of vanadium were investigated and the roasted samples were characterized by TG-DSC, XRD, and SEM. The leaching ratio of vanadium can be significantly enhanced with the increasing in roasting temperature, m (CaO)/m (V₂O₅), and roasting time. The leaching ratio of chromium decreased with roasting temperature and increased with m (CaO)/m (V₂O₅), and roasting time. The optimal roasting parameters were roasting temperature of 850 °C, the m (CaO)/m (V₂O₅) of 0.85, and roasting time of 90 min. Under the optimal roasting parameters, the leaching ratio of vanadium reached 88.81%. While the leaching ratio of chromium is 3.98%. During roasting process, vanadium is oxidized to acid-soluble CaV₂O₅, Ca₂V₂O₇, and CaMgV₂O₇. After leaching, chromium mainly exists in form of chromohercynite (FeCr₂O₄) and chrome-manganese spinel (Mn_1.5Cr_1.5O₄) in leaching residues.

Abstract: The effect of point defects on the shear rupture resistance in titanium aluminide is investigated by the density functional theory and pseudopotential methods. Vacancies, as well as substitution atoms – tungsten and chromium were considered as points defects. The shear was simulated in the(111) slip plane for two directions, namely [110] and [11-2]. It is shown that for a {111}<110> sliding system, vacancies significantly reduce the shear resistance. However, when alloying element occupies a titanium vacancy, it can partially compensate for this negative effect.

Abstract: The crystal structure of the (Cr,Ni)₄Si phase with and without Co was refined from X-ray powder diffraction data. The compound crystallises with an Au₄Al-type structure (Pearson symbol cP20, space group P2₁3): unit-cell parameter a = 0.611959(6) nm for the composition (Cr_0.312Ni_0.688)₄Si, a = 0.612094(6) nm for (Cr_0.375Ni_0.625)₄Si, and a = 0.612316(6) nm for (Cr_0.337Co_0.063Ni_0.600)₄Si. The magnetic susceptibility was measured in external fields up to 7 T at temperatures between 1.8 and 400 K. The three investigated samples exhibited paramagnetic behaviour described by the modified Curie-Weiss law: χ₀ = 146∙10^-6 emu g-at.^-1, μ_eff = 0.21 μ_B/atom, θ_P = -13 K for (Cr_0.312Ni_0.688)₄Si; χ₀ = 158∙10^-6 emu g-at.^-1, μ_eff = 0.20 μ_B/atom, θ_P = -15 K for (Cr_0.375Ni_0.625)₄Si; χ₀ = 169∙10^-6 emu g-at.^-1, μ_eff = 0.18 μ_B/atom, θ_P = -52 K for (Cr_0.337Co_0.063Ni_0.600)₄Si.

Abstract: Catalyst of Chromium (Cr) metal supported on sulfated zirconia (SZ) was prepared by wet impregnation method. This study aim to determine the optimal concentration of Cr metal that impregnated on SZ catalyst. Preparation of catalyst was conducted at different concentrations of Cr metal (0.5%, 1%, 1.5% (w/w)), impregnated on SZ catalyst, then followed by the calcinationand reduction process. Catalysts were charaterized by FTIR, XRD, XRF, SAA, TEM, and acidity test. The results showed the Cr/SZ 1% had the highest acidity value of 8.22 mmol/g which confirmed from FTIR spectra. All the crystal phase of these catalysts were in monoclinic. The specific surface area increased with the increasing of Cr metal concentration on SZ catalyst and the isotherm adsorption-desorption of N₂ gas observed all the catalysts as mesoporous material. The impregnation process formed particles agglomeration.

Abstract: Restrictions and control on the use of fatliquor especially the sulphited oil during leather production is required due to its effect on chromium change valence (from Cr(III) to Cr(VI)). Utilization of the other oil sources such as vegetable or mineral oil is worthed to be a substitute material. The aim of this study is to quantify the potential release of Cr(III) and Cr(VI) from different fatliquors and find the alternative fatliquor. The results showed that the use of 10% mineral oil and sulphited oil affected the Cr total and formation Cr(VI) in the leather, while using 6% condensed tannin (Mimosa) as an antioxidant is effective to reduce the Cr total and Cr(VI) contents in the leather.

Abstract: The problem of processing slimes of galvanic production, formed as a result of neutralization of technological solutions and wastewater containing heavy non-ferrous metals is considered. At present, sludges are transported to disposal area and are not used in any way. Typically, such sludges contain significant amounts of chromium and nickel, which creates environmental hazard. Investigated sludge of Dimitrovgrad Automobile Units Plant (Russia) contains up to 6.6% Ni and up to 7,4% Cr. The hydrometallurgical process is proposed to treatment of these sludges. Solutions of sulfuric acid, ammoniaс chloride and Trilon B were used as lixiviants. It is shown that when using a solution of sulfuric acid with pH=1,5, extraction of up to 93,3% Cu, 70,2 Ni, 90,3 Zn is achieved.

Abstract: Adsorption of Cr(III) and Cr(VI) in aqueous solution by the zeolite A from coal fly ash at various conditions has been carried out. Zeolite A was synthesized from fly ash through modified alkaline fusion hydrothermal process in a reactor stainless steel. Adsorption is carried out by direct contact between the adsorbent and adsorbate in an adsorption batch. Zeolite A from fly ash (ZA-FA) of 0.01 g was mixed with 20 mL both Cr(III) and Cr(VI) at various pH, contact time and initial concentration, in a flask Erlenmeyer 50 mL. The result showed that pH conditions of adsorption process, affect the adsorption ability of zeolite A to Cr(III) and Cr(VI) in aqueous solution. The adsorption of Cr(III) and Cr(VI) on zeolite A reached a maximum at pH 6 and time contact 120 minutes. The adsorption of Cr(III) on zeolite A increased from 3.4 mg/g at pH 3 and achieved a maximum adsorption of 42.67 mg/g at pH 6. At higher pH (7-8) the Cr(III) adsorption tends decreases. The adsorption ability of ZA-FA to Cr(III) is higher than that of Cr(VI) in aqueous solution. The Cr(III) adsorption process on ZA-FA follows the pseudo-order 2 kinetics model.

Abstract: The paper presents the results of modelling of phosphorus interaction with substitutional (Cr, Mn, P) and interstitial (C) impurity atoms in bcc iron in the framework of density functional theory using WIEN2k software. It is found that a repulsion exists of a phosphorus atom in the three first spheres of coordination of carbon, chromium and phosphorus atoms, while for manganese such repulsion of phosphorus takes place only in the second sphere. This repulsion is a consequence of an abrupt change of magnetic moment of manganese atom, so the solution energy of phosphorus almost does not change. On the contrary, chromium decreases phosphorus solubility in iron, in agreement with other data.

Abstract: This work is in addition to the various works undertaken by the researchers, using biomass as adsorbent. However, the aim of this study is the recovery of a marine material alga: Ulva lactuca) that we were able to transform into adsorbent with treatment under physical carbonization and chemical activation. The ability of treated and untreated Ulvala ctuca, to remove hexavalent chromium Cr (VI) ions in aqueous solutions was investigated. The influence of pH, sorbent dose, initial concentration, temperature, and contact time has been studied in batch process. The materials are characterized by FTIR and SEM analysis. The highest Cr (VI) removals (100%) were achieved at pH of 3, particle size of less than 250μm, dose of 1 g/L, and equilibrium time of 180 minutes. Thermodynamic results indicated that the Cr (VI) adsorption process was spontaneous and exothermic. The adsorption data fit well with Langmuir isotherm model with a maximum adsorption capacities (q_max) of untreated and treated Ulva lactuca were between 0.6 and 2 mg/g. Higher Cr (VI) removal revealed the practical applicability of Ulva lactuca in water and wastewater treatment systems.