Showing papers on "Chromium published in 1996"
TL;DR: This work focuses on the surface chemistry and spectroscopy of chromium in inorganic oxides and the mechanics of hydrogenation-dehydrogenation reactions.
Abstract: Focuses on the surface chemistry and spectroscopy of chromium in inorganic oxides. Characterization of the molecular structures of chromium; Mechanics of hydrogenation-dehydrogenation reactions; Mobility and reactivity on oxidic surfaces.
728 citations
TL;DR: In this paper, a molecular-based ferrimagnetic thin films with high critical temperatures (Tc) composed of mixed-valence chromium cyanides were synthesized by means of a simple electrochemical route.
Abstract: Molecular-based ferrimagnetic thin films with high critical temperatures (Tc) composed of mixed-valence chromium cyanides were synthesized by means of a simple electrochemical route. The highest Tc was 270 K, obtained for Cr2.12(CN)6. The Tc values were easily controlled by changing the preparation conditions. Moreover, a reversible shift of Tc could be electrochemically induced. As a result of such electrochemical control, these cyanides can be switched reversibly back and forth between ferrimagnetism and paramagnetism. These magnets thus represent materials in which magnetic properties are combined with electrical functions.
549 citations
TL;DR: In this article, the potential of the Cr-containing vapor species for the degradation of the electrical properties of an SOFC was analyzed by thermodynamic computations, and partial pressures of the vaporizing species were determined for different O 2 and H 2 O concentrations in the oxidizing gas.
Abstract: Alloys protected from corrosion by a chromia scale and LaCrO{sub 3}-based perovskites are used as materials for the interconnect of solid oxide fuel cells (SOFCs). The chromium vaporization of these materials was studied by thermochemical modeling. Partial pressures of the vaporizing species were determined for different O{sub 2} and H{sub 2}O concentrations in the oxidizing gas. CrO{sub 2}(OH){sub 2}(g) and CrO{sub 3}(g) are the most abundant species in air with and without humidity, respectively. The potential of the Cr-containing vapor species for the degradation of the electrical properties of an SOFC was analyzed by thermodynamic computations. The electrochemical reduction of the Cr-containing vapor species at the cathode/electrolyte/gas phase boundary can lead to polarization losses.
498 citations
TL;DR: Serum and urine metal concentrations may be useful markers for the tribologic performance of metal on metal bearings in total hip arthroplasty.
Abstract: There has been a resurgence of interest in the use of metal on metal bearings in total hip arthroplasty. Although the use of metal on metal bearing couples would eliminate or substantially reduce particulate polyethylene generation (depending on the presence or absence of polyethylene in the implant system), there is concern about the potential for increased particulate and ionic metal generation in comparison with polyethylene on metal bearings. These metallic degradation products may be transported away from the implant site and distributed systemically. Chromium concentrations in the serum and urine and cobalt concentrations in the serum were measured in subjects with cobalt chromium alloy metal on metal total hip replacements and in controls without implants. Eight subjects with long term (> 20 years) McKee-Farrar total hip replacements had 9-fold elevations in serum chromium, 35-fold elevations in urine chromium, and at least 3-fold elevations in serum cobalt concentrations in comparison with controls. Six subjects with short term (< 2 years) metal on metal surface replacement arthroplasties had 3-fold elevations in serum chromium, 4-fold elevations in urine chromium, and 4-fold elevations in serum cobalt concentrations in comparison with subjects with McKee-Farrar implants. Although the toxicologic importance of these trace metal elevations has not been established, serum and urine metal concentrations may be useful markers for the tribologic performance of metal on metal bearings.
350 citations
322 citations
TL;DR: In this paper, the development of the microstructure in high chromium white irons through solidification and thermal processing is discussed, and the metallurgical effects of conventional processing techniques are discussed.
Abstract: High chromium white irons are ferrous based alloys containing 11–30 wt-% chromium and 1.8–3.6 wt-% carbon, with molybdenum, manganese, copper, and nickel sometimes added as additional alloying elements. The microstructure of these alloys typically consists of hard primary and/or eutectic carbides in a matrix of austenite or one of its transformation products. The presence of hard alloy carbides results in excellent abrasion resistance and, consequently, these alloys are commonly used for materials handling in the mining and minerals processing industries. Alloy content, solidification parameters, and thermal processing can dramatically alter the microstructure that is produced, and this in turn can influence the properties and hence performance of white iron alloys during service. This review outlines the development of the microstructure in high chromium white irons through solidification and thermal processing. The metallurgical effects of conventional processing techniques are discussed, and ad...
292 citations
TL;DR: In this article, an initial coverage of the alumina support occurs, constituted of Cr 6+ species anchored to the support, and of dispersed Cr 6+, Cr 3+, and Cr 3+ oxide species.
289 citations
202 citations
TL;DR: The complex chemistry of chromium compounds presents unique measurement and regulatory challenges and the challenges of measuring and regulating these compounds are unique.
Abstract: The complex chemistry of chromium compounds presents unique measurement and regulatory challenges.
201 citations
15 Jul 1996-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the growth mechanism of Cr2O3 scales was studied at 900 and 800 °C by determining diffusivities, both in bulk and along the grain boundary, of 18O and 54Cr in Cr2 O3 scales formed on a Ni70Cr30 alloy with and without yttrium implants (1016 ions cm−2).
Abstract: The growth mechanism of Cr2O3 scales was studied at 900 and 800 °C by determining diffusivities, both in bulk and along the grain boundary, of 18O and 54Cr in Cr2O3 scales formed on a Ni70Cr30 alloy with and without yttrium implants (1016 ions cm−2). The diffusion of 18O and 54Cr was carried out simultaneously which allowed us to obtain a direct comparison of self-diffusion. All the concentration profiles were established by SIMS. Without yttrium in Cr2O3 scales, the oxygen bulk diffusion coefficient is close to that of chromium, but the chromium grain boundary diffusion coefficient is greater than that of oxygen. The presence of yttrium in Cr2O3 scales slightly decreases the grain boundary diffusivities of18O and 54Cr, but enhances the oxygen lattice diffusion. The parabolic oxidation constant rates calculated from our diffusion data according to Wagner theory, were close to the experimental ones determined by oxidation kinetic tests. It is concluded that the Cr2O3 scale growth is controlled by counter-current diffusion of oxygen and chromium for the unimplanted and implanted alloys, mainly by grain boundary diffusion. Yttrium does not change the growth mechanism.
174 citations
TL;DR: In this article, a simple method for the determination of chromium(III) and total chromium in a flow injection system comprising chelating ion exchange and flame atomic absorption spectrometry (FAAS) was described.
TL;DR: To identify DNA groups involved in the ternary complex formation, pre-formed Cr(III)-histidine complexes were reacted with nucleosides and nucleotide monophosphates followed by separation and analysis of the products.
Abstract: We have recently shown that a substantial fraction of all Cr−DNA adducts in chromate-exposed cells are represented by ternary complexes involving amino acids or glutathione bridged by Cr(III) to DNA. The tridentate amino acids such as cysteine, glutamic acid, and histidine were predominantly found cross-linked to DNA. The mechanism by which Cr can cross-link these amino acids to DNA has been modeled by reacting DNA and trivalent and hexavalent chromium with cysteine and histidine. The formation of a Cr(III)−amino acid binary complex was required before Cr(III) reacted with DNA to yield a ternary complex. Cr(III)-pretreated DNA did not bind cysteine or histidine even after prolonged incubations. Reduction of Cr(VI) in the presence of DNA gave rise to an extensive cross-linking of cysteine and histidine. Addition of DNA to Cr(VI) mixtures at the start of reduction or after the reduction was complete had little effect on the level of ternary complexes indicating that Cr(III)−amino acid binary complexes were ...
TL;DR: It is suggested that routine chromium supplementation has no beneficial effects on body- composition change or strength gain in men and whether chromium supplements of individuals with diminished chromium nutriture facilitates propitious changes in body structure and function remains to be determined.
TL;DR: In this paper, the authors present direct in situ X-ray absorption fine structure (XAFS) evidence for the presence of hexavalent chromium(III) at the surface of synthetic magnetite at near neutral pH.
TL;DR: It is demonstrated that Cr concentrations are greatest in the kidney and that the form of dietary Cr significantly affects tissue Cr concentrations, and blood Cr is not in equilibrium with tissue Cr stores.
Abstract: Chromium (Cr) absorption is low (<1%) and there is a need to find Cr compounds that are absorbed better than inorganic Cr salts. Therefore, the incorporation of nine different chromium (Cr) compounds on tissue Cr concentration of 6-week male Wistar rats was investigated. Chromium compounds tested were Cr chloride (Cr chloride), Cr acetate (Cr acetate), Cr potassium sulfate (CrAlum), Cr trihistidine (Cr histidine), Cr triglycine (Cr glycine), Cr trinicotinic acid (CrNA), Cr dinicotinic acid dihistidine (CrNA-HIS), Cr tripicolinic acid (Cr picolinate), and Cr dinicotinic acid diglycine cysteine glutamic acid (CrNA-AA). Complexes were fed to weanling rats for 3 weeks at 5,000 ng of Cr/g of diet. Basal control diet was a cornstarch-based diet containing 30 ng Cr/g. Chromium incorporation into the kidney was greatest for CrNA-AA complex (850 ng/g dry wt) followed by CrAlum (407 ng/g), Cr acetate (397), CrNA-HIS (394), Cr picolinate (368), Cr glycine (343), Cr nicotinate (166), Cr chloride (74), CrHIS (49), and control (23 ng/g). Chromium concentration of the liver was greatest for the Cr picolinate compound (50 ng/g) followed by CrNA-AA and Cr acetate. Liver Cr concentrations of remaining complexes were not significantly different from those of the control animals that received no added Cr. Chromium concentrations were significantly greater in the kidney than those for the liver, spleen, heart, lungs, and gastrocnemius muscle. Supplemental Cr did not affect tissue zinc and copper but did alter tissue iron concentrations. Absorption of radioactive forms of Cr did not explain the differences in tissue Cr concentrations. Chromium absorption after 4 hours and retention after 24 hours were not significantly different for the forms of Cr tested. These data demonstrate that Cr concentrations are greatest in the kidney and that the form of dietary Cr significantly affects tissue Cr concentrations. Absorption of Cr does not correlate with tissue Cr concentrations and blood Cr is not in equilibrium with tissue Cr stores. © 1996 Wiley-Liss, Inc. This article is a U.S. Government work and, as such, is in the public domain in the United States of America.
TL;DR: In this article, the uptake of copper(II) and chromium(VI) ions from binary mixtures by Rhizopus arrhizus is described as a function of ion concentration, pH and temperature.
TL;DR: It is suggested that the combination of GSH, molecular oxygen, and chromium(VI) can damage DNA via non-Fenton pathways.
TL;DR: The data suggest that nearly all the ingested Cr(VI) was reduced to Cr(III) before entering the bloodstream based on comparison to RBC and plasma chromium patterns in animals exposed to high doses of Cr( VI).
TL;DR: In this article, the sliding wear resistance of stainless steel components, carbide-hardened surfaces were produced on AISI 316L austenitic stainless steel by laser surface alloying.
Abstract: In order to improve the sliding wear resistance of stainless steel components, carbide-hardened surfaces were produced on AISI 316L austenitic stainless steel by laser surface alloying. Different powdered precursors (Cr3C2, a mixture of Cr3C2 and Cr and a mixture of Ti and SiC) were applied to the steel surface and irradiated using a continuous wave, 300 W, Nd-YAG laser. The surface alloys resulting from the incorporation of Cr3C2 alone or mixed with chromium were composed of austenite (y) dendrites surrounded by a γ-M7C3 eutectic (M≡Fe or Cr); their microhardness ranged from 380 to 450 HV. Superficial hardening by titanium carbide was obtained using a mixture of Ti and SiC powders as precursors; Ti and SiC particles dissolved in the melted pool, leading to the precipitation of fine TiC particles during solidification. The microhardness of the surface alloy was about 350 HV. For both chromium carbide and titanium carbide surface alloying treatments, the processing conditions were determined which led to a noticeable improvement of the sliding wear resistance of AISI 316L stainless steel without any detrimental effect on its high temperature oxidation resistance.
TL;DR: The potential energy surface of the triatomic cation [Cr,O2]+ has been examined by means of ion-cyclotron resonance and sector-field mass spectrometry as well as high-level theoretical methods as mentioned in this paper.
Abstract: The potential-energy surface of the triatomic cation [Cr,O2]+ has been examined by means of ion-cyclotron resonance and sector-field mass spectrometry as well as high-level theoretical methods. Chromium(V) dioxide cation OCrO+ can be generated by electron ionization of CrO2Cl2 and exhibits a doublet ground state. The experimentally determined IE(CrO2) of 9.7 ± 0.2 eV leads to ΔHf(OCrO+) = 209 ± 12 kcal/mol which compares well with a theoretical prediction of 217 kcal/mol. The high-valent chromium(V) dioxide OCrO+ slowly reacts with H2 to form CrO+ and H2O as products. Activation of saturated and unsaturated hydrocarbons, including methane and benzene, is much more efficient and involves C−H as well as C-C bond activation. In the reaction of OCrO+ with CH4 the by-product OCr(OCH2)+ points to the operation of a stepwise mechanism in that initially a single oxo unit in OCrO+ is activated in terms of a [2 + 2] cycloaddition of methane across the Cr−O double bond. A structurally different [Cr,O2]+ cation can b...
TL;DR: In this article, the release behavior of chromium from tannery sludge was assessed, and the equilibrium solubility was first conducted when the pH value was maintained at 4.2, and varied redox potential (0, 150, 250, 320, 470 mV).
TL;DR: In this paper, a process of fully competitive biosorption of chromium(VI) and iron(III) ions to Rhizopus arrhizus from binary metal mixtures is described and compared to single metal-ion situations in solution.
TL;DR: Chromium(III) alkyls featuring an amido ligand tethered to a permethylcyclopentadienyl ring (i.e. [η5-Me4C5SiMe2-η1-NtBu]CrR) have been prepared and structurally characterized.
TL;DR: An infinite stair-like layered ferromagnetic system was obtained from the reaction of K3[CrIII(CN)6] with [NiII-(cyclam)][ClO4]2(cyclam = 1,4,8,11-tetraazacyclotetradecane) as discussed by the authors.
Patent•
27 Nov 1996
TL;DR: In this article, positive electrodes including a lithium nickel cobalt metal oxide are disclosed, where the general formula Li x Ni y CO z M n O 2, where M is selected from the group consisting of aluminum, titanium, tungsten, chromium, molybdenum, magnesium, tantalum, silicon, and combinations thereof, x is between about 0 and about 1 and can be varied within this range by electrochemical insertion and extraction, the sum of y+z+n is about 1, n ranges between above 0 to about 0.25, y and
Abstract: Positive electrodes including a lithium nickel cobalt metal oxide are disclosed. The lithium nickel cobalt metal oxides have the general formula Li x Ni y CO z M n O 2 , where M is selected from the group consisting of aluminum, titanium, tungsten, chromium, molybdenum, magnesium, tantalum, silicon, and combinations thereof, x is between about 0 and about 1 and can be varied within this range by electrochemical insertion and extraction, the sum of y+z+n is about 1, n ranges between above 0 to about 0.25, y and z are both greater than 0, and the ratio z/y ranges from above 0 to about 1/3. Also disclosed are composite positive electrodes including the abovedescribed lithium nickel cobalt metal oxides together with a lithium manganese metal oxide of the formula Li x Mn 2-r M1 r O 4 , where r is a value between 0 and 1 and M1 is chromium, titanium, tungsten, nickel, cobalt, iron, tin, zinc, zirconium, silicon, or a combination thereof.
TL;DR: In this article, (Ti1−xCrx)N coatings with different Ti/Cr ratios were deposited on polished high speed steel substrates by reactive magnetron sputtering and oxidized in air at temperatures between 350 and 800 °C, with reaction times between 10 and 300 min.
TL;DR: In this article, a mixed plating rinse wastewater containing zinc, hexavalent chromium, trivalent and cyanide with total dissolved solids of 424 mg/1 was treated by a model consisting of a sand filter and ion exchange columns.
TL;DR: In this article, the same substitution was shown by congruent dissolution of Fe and V and by the presence of Fe2+ equivalent to structural V in an acid digest on heating up to 800°C.
TL;DR: In this paper, a coprecipitation method was used to synthesize hydrotalcite-like compounds containing Mg(II) and Cr(III) cations in the Brucitelike layers.
Abstract: Hydrotalcite-like compounds containing Mg(II) and Cr(III) or Ni(II) and Cr(III) cations in the brucite-like layers have been synthesized by the coprecipitation method. The layered structure has been confirmed by Powder X-ray diffraction, and characterization has been completed by elemental chemical analysis, FT-IR and vis−UV/diffuse reflectance spectroscopies, and thermal analysis (differential thermal analysis and thermogravimetric analysis). The behavior shown during the thermal studies depends on the atmosphere used to carry out the study; a weak endothermic effect, at temperatures coinciding with a small weight loss, is recorded when the analysis is performed in air but not when performed in nitrogen, and so it is ascribed to oxidation processes. Formation of chromate-like species in the samples calcined at intermediate temperatures has been confirmed by powder X-ray diffraction for sample MgCr-HT and is suggested by FT-IR spectroscopy for sample NiCr-HT; the lack of success in identifying chromate-li...