Showing papers on "Chromium published in 1969"

Chromium occurrence and function in biological systems.

Abstract: An extensive review of the biogeochemistry of chromium is presented. Topics dealt with in detail include: the chemistry of chromium, its occurrence in nature, chromium's interactions with proteins, nucleic acids, bacteria, yeasts and red blood cells, the biochemical aspects of low-chromium states, the effects of chromium on life span, growth, and survival, the mode and site of action in biological systems, the metabolism (including absorption, distribution, excretion, and toxicology) the effects of chromium's chemical form on biological activity, chromium nutrition in man, and the effects of chromium supplementation in man). 265 references, 12 figures, 8 tables.

Optical Spectra of Cr3+ Impurity Ions in Ferroelectric LiNbO3 and LiTaO3

Abstract: The optical absorption, luminescence, and excitation spectra of LiNbO3 and LiTaO3 doped with chromium impurities are examined as a function of temperature. Several interesting differences between these spectra and those of other chromium‐doped oxides are noted. The most important differences are the large halfwidth of the Cr3+‐ion “R” lines (∼50 cm−1 at 4.2°K) and the absence of any “R”‐line luminescence down to 4.2°K. Instead, a broadband emission peaking at about 1 μ is observed. It is shown that these differences arise from the low value of the crystal‐field parameter Dq at the Cr3+‐ion site in LiNbO3 and LiTaO3, so that the zero‐phonon 4T2 state of the Cr3+ ion lies at a lower energy than the 2E state. Point‐charge calculations of Dq for several oxides, including LiNbO3 and LiTaO3, and other considerations suggest that the most probable sites of the Cr3+‐ion impurities are the Nb/Ta sites and not the Li sites.

Volume and Grain-Boundary Diffusion in 20 Cr/25 Ni/Nb Stainless Steel

Abstract: Standard radiotracer techniques have been used to measure the volume-diffusion rates of chromium and nickel in a 20 Cr/25 Ni/Nb austenitic steel in the temperature range 840–1290° C. Within the limits of experimental uncertainty, the results are described by D Cr = 0·19 exp (−58·8 × 103/RT), D Ni = 4·06 exp (−67·5 × 103/RT). Grain-boundary-diffusion measurements have been made in the range 550–900° C. The diffusion rates of chromium and nickel isotopes are not significantly different from previously reported values for iron. Combining the data for all three elements gives a mean Arrhenius equation δDB = 1·5 × 10−7 exp (−44 × 103/RT).

Chromium carcinogenesis: calcium chromate as a potent carcinogen for the subcutaneous tissues of the rat.

Abstract: Chromium carcinogenesis: calcium chromate as a potent carcinogen for the subcutaneous tissues of the rat.

Magnetic Properties of FeCr2S4 and CoCr2S4

Abstract: New measurements of magnetic properties of pure FeCr2S4 and CoCr2S4 have been carried out. The g-factors of cobalt, iron, and chromium in these compounds were evaluated. Exchange interactions were deduced from computation of the experimental paramagnetic and magnetization curves.

Oxidation of Co‐25 w/o Cr at High Temperatures

Abstract: Studies of the oxidation behavior of Co‐25 w/o Cr at temperatures between 900° and 1300°C and oxygen pressures in the range 0.2–760 Torr are reported and analyzed. The oxidation behavior of this alloy is complex and does not follow a single mechanism. The parabolic rate constant at high oxygen pressures in the temperature range of 900°–1300°C is about two orders of magnitude larger than that at low oxygen pressures . The scales formed at high oxygen pressures have a duplex structure, the outer layer being virtually pure as in Co‐10 w/o Cr (1,2), and the inner layer being mainly the spinel with small amounts of and ( is concentrated near the alloy‐scale interface). At low oxygen pressures, the morphology of the scale is dependent on the radius of curvature of the specimen; at the edges where this radius is small, the structure is similar to the structure developed at high oxygen pressures; on the large surfaces, is the dominant oxide.The mechanism of parabolic oxidation of Co‐25 w/o Cr at high oxygen pressures involves cobalt‐ion diffusion through a network in the inner layer. Initial oxidation under these conditions is nonparabolic and this is due to selective oxidation of chromium to which takes place when the specimens are exposed to the "vacuum" of the reaction furnace prior to the start of the actual oxidation run. The transition from the high‐ to low‐pressure oxidation is due to a transition to selective oxidation of chromium. The oxidation is then governed by diffusion of the reacting ions (probably chromium) through the scales.

Effects of addition of copper, manganese, zinc and chromium compounds on ammonification and nitrification during incubation of soil

Abstract: The effects of adding 100, 1,000, and 10,000 ppm of copper, manganese, zinc and chromium as sulphates and of copper and zinc as carbonates on ammonification and nitrification during incubation (3) weeks) of an initially neutral soil under aerobic and anaerobic conditions were studied. Some stimulating but more usually inhibitory effects of trace elements on both processes were found. These effects varied considerably depending on the level and type of the cation added, whether the conditions were aerobic or anaerobic, and on the extent to which pH was altered by the treatments.

Thermal expansivities, thermal conductivities, and densities of vanadium, titanium, chromium and some vanadium-base alloys: A comparison with austenitic stainless steel

Abstract: Computer-fitted polynomial expressions are presented that define the linear thermal-expansion behavior of vanadium, titanium, chromium, certain VTi and VTiCr alloys, and AISI Types 304 and 316 stainless steels between 0 ° and 1000 °C. The mean expansion coefficients for the vanadium-base alloys differ only slightly from those for unalloyed vanadium (plus or minus 6%), and are 65% to 80% lower than the mean expansion coefficients for the austenitic stainless steels. Densities of the vanadium-base alloys and the austenitic stainless steels were determined at 25 °C by liquid displacement. The VTi alloys show a non-linear decrease in density with increasing titanium for titanium contents greater than 30 wt.%. The VTiCr alloys also exhibit a non-linear change in density for compositions containing greater than 15 wt.% titanium, and greater than 5 wt.% chromium. A comparison of the mechanical and thermal properties of two vanadium-base alloys and two austenitic stainless steels was made to determine their relative usefulness as reactor fuel jackets for service between 500 ° and 700 °C. This comparison shows that vanadium alloy fuel jackets would be subjected to only one-third the thermal stresses generated in austenitic stainless steel jackets during reactor excursions between 500 ° and 700 °C under conditions where the fuel is not in intimate contact with the jacket. This difference in thermal stresses in the two jacket materials is the result of the 37% higher tensile strength, 40% higher thermal conductivity, and 70% lower thermal expansivity exhibited by the vanadium alloys as compared with austenitic stainless steel.

Composite coating for the superalloys

Abstract: Improved operating lifetimes are provided for the superalloys through use of a composite coating comprising a chromium or chromium-rich interlayer adjacent the superalloy substrate surface and an oxidation-resistant outer layer comprising an alloy of iron, cobalt and/or nickel alloyed with selected amounts of chromium, aluminum and yttrium.

Nickel base superalloy resistant to oxidation erosion

Abstract: Nickel-base superalloys are described which oxidize selectively to form a single protective oxide Al2O3 which is particularly adherent to the alloy surface. Alloys of the nickel-chromiumaluminum type are disclosed in a basic chemistry corresponding to, by weight, 4-7 percent aluminum, 12-21 percent chromium, 1925 percent aluminum plus chromium, 0.01-0.5 percent yttrium or similar material, balance nickel with the usual alloying ingredients associated with the superalloys.