Showing papers on "Chromium published in 1987"
608 citations
TL;DR: In this article, the chemical changes induced by 4-keV Ar/sup +/bombardment of the transition-metal oxyanion compounds N/sub 2/WO/sub 4/ (N = Li, Na, Ag, NH/sub4/), Na/sub x/MO/sub y/ (M = V, Cr, Nb, Mo, Ta), and the corresponding transition metal oxides have been investigated by x-ray photoelectron spectroscopy (XPS).
Abstract: The chemical changes induced by 4-keV Ar/sup +/bombardment of the transition-metal oxyanion compounds N/sub 2/WO/sub 4/ (N = Li, Na, Ag, NH/sub 4/), Na/sub x/MO/sub y/ (M = V, Cr, Nb, Mo, Ta), and the corresponding transition-metal oxides have been investigated by x-ray photoelectron spectroscopy (XPS). Both the atomic concentrations and the binding energy shifts in the altered layer show that a steady-state composition is attained at a total irradiation dose of approx.10/sup 17/ ions/cm/sup 2/. Bombardment of all of the oxyanions resulted in reduction of the transition-metal atoms to lower oxidation states; reduction to the metallic state is observed in all cases except VO/sub 3//sup -/ and CrO/sub 4//sup 2 -/. In contrast, bombardment of the metal oxides produced lower oxidation states of the metal in some, but not all, cases. The mechanism of ion-induced decomposition is discussed in terms of the thermal spike model and the behavior of specific compounds is shown to correlate with decomposition pressure at elevated temperatures.
192 citations
171 citations
TL;DR: In the present paper, a direct demonstration of intracellular chromium reduction is provided by means of electron paramagnetic (spin) resonance (EPR) spectroscopy.
167 citations
126 citations
TL;DR: The influence of cold work on the initially formed oxide layer on the stainless steels AISI 304 and Incology 800H has been studied by XPS as mentioned in this paper, which showed a similar oxidation behavior.
116 citations
TL;DR: In this article, the authors measured the oxidation rate of NaCl-coated chromium over the temperature range of 823-1043 K. Although the melting point of NaCL is 1074 K, accelerated oxidation was observed at every temperature.
Abstract: The oxidation rate of NaCl-coated chromium was measured over the temperature range of 823–1043 K. Although the melting point of NaCl is 1074 K, accelerated oxidation was observed at every temperature. Oxidation mass-gain curves were divided into two types. Type I involved only accelerated oxidation during the initial stage followed by the formation of a thin protective Cr2O3 film. Type II pertained to an acceleration over a long time, forming a thick and nonprotective Cr2O3film containing Na2CrO4. The former type of oxidation occurred at lower temperatures or with a small amount of NaCl, whereas the latter occurred at higher temperatures and with large amounts of NaCl. A comparison of these oxidation processes with those by CaCl2 or BaCl2, revealed two problems: (1) Why was the oxidation rate of chromium so high in the presence of NaCl?, and (2) Why did the high oxidation rate continue for such a long time?
116 citations
TL;DR: In this paper, an α,β-unsaturated carbonyl compound was converted into α,α-β -unsaturated β-carbinear compounds using excess of tert.butylhydroperoxide and catalytic amounts of chromium VI oxide at room temperature.
91 citations
87 citations
Patent•
11 Feb 1987
TL;DR: Chlorine can be efficiently produced at a low temperature and with a high hourly space velocity by oxidizing hydrogen chloride with an oxygen-containing gas in the presence of a catalyst obtained by calcining a compound, which has in turn been obtained by reacting chromium nitrate, chromium chloride, the chromium salt of an organic acid or the like with ammonia.
Abstract: Chlorine can be efficiently produced at a low temperature and with a high hourly space velocity by oxidizing hydrogen chloride with an oxygen-containing gas in the presence of a catalyst obtained by calcining a compound, which has in turn been obtained by reacting chromium nitrate, chromium chloride, the chromium salt of an organic acid or the like with ammonia, or by calcining a mixture of the compound and a silicon compound, preferably, at a temperature lower than 800° C.
86 citations
TL;DR: In vitro studies on the uptake and oxidation of glucose by liver slices from chicks fed the basal diet were conducted and a chromium vanadium antagonism was observed in some metabolic processes but not on body or organ weight.
TL;DR: In this paper, an alloy containing 2% Cr and 5% Cr was shown to arise by a uniform, primary-solidification mode prior to, and independent of, the nucleation and growth of the lower ribbon surface.
TL;DR: In this article, the effects of chromium and manganese on phosphorus segregation and intergranular embrittlement were examined by hydrogen-decarburization of the original low carbon (10-60 ppm) alloys.
Abstract: Vacuum melted electrolytic iron and alloys of Fe–P, Fe–Mn, Fe–Cr, Fe–Mn–P, and Fe–Cr–P were employed in a study of the effects of chromium and manganese on phosphorus segregation and intergranular embrittlement. The effects of carbon were examined by hydrogen-decarburization of the original low carbon (10–60 ppm) alloys. The critical fracture stress was measured by pure bending of notched bars at 133 K, and the grain boundary compositions were measured by Auger electron spectroscopy. Manganese was found to segregate in the absence of phosphorus and to be a powerful embrittling element. Carbon was found to exert a great intergranular strengthening effect. It also interfered with the segregation of phosphorus; the latter effect was reduced by the presence of chromium, in agreement with the prior report of Erhart and Grabke. In decarburized alloys the presence of manganese caused increased phosphorus segregation but not when carbon was present at 10–30 ppm. Segregation of manganese and chromium were ...
TL;DR: In this article, after annealing at 1100 and 1200 °C, the diffusion coefficient of Ni-Cr-Al diffusion couples was studied and the location of maxima and minima in the concentration profiles of several of the diffusion couples indicated that both cross-term diffusion coefficients for Cr and Al are positive and that DCrAl has a greater effect on the diffusion of Cr than does DA1Cr on diffusion of Al.
Abstract: Interdiffusion in Ni-rich, Ni-Cr-Al diffusion couples was studied after annealing at 1100 and 1200 °C. Recession of γ′ (Ni3Al structure), β (NiAl structure), or α (bcc) phases was also measured. Aluminum and chromium concentration profiles were measured in the γ (fcc) phase for most of the diffusion couples. The amount and location of Kirkendall porosity suggests that Al diffuses more rapidly than Cr which diffuses more rapidly than Ni in the γ phase of Ni-Cr-Al alloys. The location of maxima and minima in the concentration profiles of several of the diffusion couples indicates that both cross-term diffusion coefficients for Cr and Al are positive and that DCrAl has a greater effect on the diffusion of Cr than does DA1Cr on the diffusion of Al. The γ/γ + β phase boundary has also been determined for 1200 °C through the use of numerous γ/γ+ β diffusion couples.
TL;DR: In this paper, the variation in hardness of the borided layer obtained on iron alloys was defined and related to an increase in chromium, nickel and carbon contents, and it was found that chromium increases the hardness both of the entire boride layer as a whole and of the components, even though these values are systematically lower than those measured on pure borides.
Abstract: The variation in hardness of the phases (Fe, M)B and (Fe, M)2B (M ≡ Cr or Ni), which are the predominant components of the borided layer obtained on iron alloys, was defined and related to increase in chromium, nickel and carbon contents. It was found that chromium increases the hardness both of the borided layer as a whole and of the boride components, even though these values are systematically lower than those measured on pure borides. Carbon, which is insoluble in this type of phase, accumulates at the boride-matrix interface and, because of its modification of the boron diffusion mechanism, it indirectly increases the hardness of the borided surface. Nickel reduces slightly but systematically the hardness of the borides, in particular of the (Fe, Ni)2B phase in which it has its highest concentration.
TL;DR: In this paper, the dissolution rates of iron, chromium, molybdenum and copper as pure metals and as components of three ferritic stainless steels in neutral solutions (distilled H2O and 0.5 M NaCl) and acid solutions (1 M and 9.2 M of HNO3 and H2SO4) are presented.
TL;DR: In this paper, the nature and the catalytic activity in the Fischer-Tropsch synthesis of cobalt, copper, zinc, and chromium mixed oxides have been investigated for a wide range of compositions.
Abstract: The nature and the catalytic activity in the Fischer-Tropsch synthesis of cobalt, copper, zinc, and chromium mixed oxides have been investigated for a wide range of compositions. Most of the precursors showed a hydrotalcite-like structure and formed by calcination essentially a spinel-type phase (notwithstanding the high values of the M(II)/M(III) ratio (M = metal)). For all catalysts the hydrocarbons were the main products and presented typical Schulz-Flory distributions. While the Co/Cr catalysts showed very low activity, a maximum was obtained for catalysts containing comparable amounts of copper and cobalt. In all samples a spinel-type phase was present after reaction, while the formation of metallic cobalt and/or cobalt oxides was not observed. On the other hand, metallic copper after both reduction and reaction was detected by N/sub 2/O titrations. The catalytic activity was attributed to a synergetic effect between copper and cobalt, correlable to the presence of a nonstoichiometric spinel-type phase or to an interaction between this phase and the well-dispersed metallic copper formed in reducing conditions.
TL;DR: In this paper, the influence of the alloying elements on the dissolution of oxygen in the metallic phase during the oxidation of titanium-based alloys was studied using microhardness measurements.
Abstract: In order to study the influence of aluminium, chromium and silicon on the dissolution of oxygen in the metallic phase during the oxidation of titanium-based alloys, unalloyed titanium Ti35 and the alloys Ti-Al (1.65, 3, 5 and 10% by weight of aluminium), Ti-Cr (1, 4, 11 and 19% by weight of chromium) and Ti-Si (0.25, 0.5 and 1% by weight of silicon) were oxidized in air and in oxygen for durations of up to several thousand hours, between 550 and 700° C. The influence of the alloying elements was studied using microhardness measurements in the metallic zone just beneath the oxide. It was observed that aluminium and silicon cause a significant reduction in the amount of oxygen dissolved in the metallic phase whereas the effect of chromium is negligible. A comparison of the oxidation behaviour of unalloyed titanium in air and in oxygen reveals the marked influence of nitrogen on the dissolution of oxygen into the substrate, causing a reduction in the amount of dissolved oxygen. In addition, for oxidation of the alloys in air, a synergistic effect is observed, particularly between nitrogen and silicon.
TL;DR: By electrothermal atomic absorption, the time course of the binding and uptake with human erythrocytes of Cr(III) compounds is investigated, finding chromium was bound and taken up significantly except with the cysteine complex which bound to the cells but sedimented with the cell envelope after cell lysis.
Abstract: Trivalent chromium is assumed to be the ultimate genotoxic form of Cr after uptake and reduction of chromate in cells. Cr(III) also is an essential trace element for mammalia; it is required for the proper control of glucose metabolism. In both kinds of biological effects, Cr(III) is assumed to act in the form of complexes with biomolecules, but there is very little information about the uptake of such complexes through membranes. By electrothermal atomic absorption we investigated the time course of the binding and uptake with human erythrocytes of [Cr(glycine)3], [Cr(2,4‐pentanedione)3], [Cr(glutathione)2]2‐, [Cr(Cysteine)2]1‐, [Cr(o‐phenanthroline)2Cl2]1+ and [Cr(bipyridine)2Cl2]1+. In all cases chromium was bound and taken up significantly except with the cysteine complex which bound to the cells but sedimented with the cell envelope after cell lysis. The uptake of Cr(III) compounds was very slow. At 1 mM concentrations and 1 hour at 37°C the intracellular chromium was estimated to be between 0.5 to 2...
Patent•
28 Dec 1987TL;DR: A TiAl composition is prepared to have high strength and to have improved ductility by altering the atomic ratio of the titanium and aluminum to have what has been found to be a highly desirable effective aluminum concentration by addition of silicon according to the approximate formula Ti59-51Al39-44Si2-5.
Abstract: RD-19,570 C-I-P of RD-17,813 5/30/89 SILICON-MODIFIED TITANIUM ALUMINUM ALLOYS AND METHOD OF PREPARATION A TiAl composition is prepared to have high strength and to have improved ductility by altering the atomic ratio of the titanium and aluminum to have what has been found to be a highly desirable effective aluminum concentration by addition of silicon according to the approximate formula Ti59-51Al39-44Si2-5.
TL;DR: In this article, the hot corrosion behavior of NaCl-coated SUS-430, SUS304,SUS-316 and SUS329J1 stainless steels was examined in a temperature range from 923 to 1173 K by thermogravimetry, measurement of corrosion loss, X-ray diffraction of the scale and electron probe microanalysis.
TL;DR: In this article, Ramaman microscopy has been used to study the nature and distribution of corrosion products formed on iron and iron-chromium alloys in air at high temperatures.
Abstract: Raman microscopy has been used to study the nature and distribution of corrosion products formed on iron and iron-chromium alloys in air at high temperatures. Fe and Fe-Cr alloys containing 2, 5, 14, and 18% Cr were oxidized at 400, 600, and 850°C for 2 hr, in addition samples of each alloy were oxidized for 24 hr at 400°C to obtain thicker scales at this temperature. The corroded samples showed varying distributions of the oxides Fe2O3, Fe3O4, Cr2O3, and FeCr2O4. Fe2O3 and Fe3O4 were formed exclusively on the pure iron and the 2 and 5% chromium alloys at all temperatures and on the 14% chromium alloy at 400°C. The 14 and 18% Cr alloys formed scales containing Cr2O3 and FeCr2O4 at the higher temperatures (600 and 850°C). Examples of small regions of Fe2O3 being formed within Cr2O3-FeCr2O4 scales are suggested as possible indications of breakaway corrosion initiation sites.
TL;DR: According to the results, chromium levels in plasma and urine in the order of 10 and 40 μg/l seem to correspond to an external exposure of 100 μg chromium trioxide per cubic metre, the technical guiding concentration (TRK-value).
Abstract: External and internal chromate exposure of 103 stainless steel welders who were using manual metal are welding (MMA), metal inert gas welding (MIG) and both methods, were measured by ambient and biological monitoring. At the working places the maximum chromium trioxide concentrations were 80 micrograms/m3. The median values were 4 micrograms/m3 (MMA) and 10 micrograms/m3 (MIG). The median chromium concentrations in erythrocytes, plasma and urine of all welders were less than 0.60, 9.00 and 32.50 micrograms/l. For biological monitoring purposes, chromium levels in erythrocytes and simultaneously in plasma seem to be suitable parameters. According to our results, chromium levels in plasma and urine in the order of 10 and 40 micrograms/l seem to correspond to an external exposure of 100 micrograms chromium trioxide per cubic metre, the technical guiding concentration (TRK-value). Chromium concentrations in erythrocytes greater than 0.60 micrograms/l indicate an external chromate exposure greater than the TRK-value.
Patent•
01 Oct 1987
TL;DR: Nickel-base alloys containing special and correlated percentages of chromium, iron, molybdenum, titanium, niobium, aluminum etc. as mentioned in this paper provide an attractive combination of strength, ductility, resistance to environmental media and other desirable characteristics.
Abstract: Nickel-base alloys containing special and correlated percentages of chromium, iron, molybdenum, titanium, niobium, aluminum etc. (i) provide an attractive combination of strength, ductility, resistance to environmental media and other desirable characteristics, (ii) can be processed by cold working and age hardening to achieve yield strengths of 150,000 psl (1034 MPa) to 200,000 psl (1379 MPa) together with tensile elongations of 10% to 20%, (iii) are resistant to such corrosive media as hydrogen sulphide and acid chloride sol-utions, and to hydrogen embrittlement, and (iv) are useful for, inter alia, petroleum production tubing and sulfur diox-ide gas scrubber applications.