Showing papers on "Chromium published in 1988"

Chromium in the natural and human environments

Abstract: Historical Perspectives (J Nriagu) Biological Chemistry of Chromium (E Nieboer & A Jusys) Production and Uses of Chromium (J Nriagu) Atmospheric Emissions of Chromium from Natural and Anthropogenic Sources (J Pacyna & J Nriagu) Distribution and Characteristic Features of Chromium in the Atmosphere (J Nriagu, et al) Geochemistry of Chromium in the Oceans (L Mayer) Occurrence and Distribution of Chromium in Natural Waters of India (B Handa) Chromium Contamination of Groundwater (L Calder) Chromium Removal from Industrial Wastewaters (S Beszedits) Mobility and Bioavailability of Chromium in Soils (R Bartlett & B James) Chromium Toxicity to Algae and Bacteria (P Wong & J Trevors) The Significance of the Interactions of Chromium and Bacteria in Aquatic Habitats (M Loutit, et al) Chromium Toxicity: Effects of Microogranisms with Special Reference to the Soil Matrix (R Coleman) Genetic Approaches in the Study of Chromium Toxicity and Resistance in Yeast and Bacteria (B--I Ono) The Toxicity of Chromium to Fish (D Holdway) Mutagenic and Other Genotoxic Effects of Chromium Compounds (E Nieboer & S Shaw) Carcinogenicity of Chromium Compounds (A Yassi & E Nieboer) Chromium Hypersensitivity (A Haines & E Nieboer) Other Health Effects of Chromium Compounds (E Nieboer & A Yassi) Index

Laser action in chromium‐activated forsterite for near‐infrared excitation: Is Cr4+ the lasing ion?

Abstract: Room‐temperature pulsed laser action has been obtained in chromium‐activated forsterite (Cr:Mg2SiO4) for excitation of the near‐infrared absorption band of the system by the 1064 nm radiation from a Nd:YAG laser. The characteristics of laser emission are similar to those observed for 532 nm pumping. It is suggested that the laser action is due to a ‘‘center’’ other than the trivalent chromium (Cr3+), presumably the tetravalent chromium (Cr4+).

An x‐ray photoelectron spectroscopic study of some chromium–oxygen systems

Abstract: A series of pure and mixed chromium standards has been analysed by x-ray photoelectron spectroscopy in order to obtain a sufficiently homogeneous and self-consistent set of spectral parameters to be used in the resolution of complex spectra. Additional information was obtained about the stability of the various species under Ar ion bombardment. The results relevant to potassium chromate and dichromate, chromous acid, chromium (III) oxide, hydroxide and nitrate are described and compared critically with those in the published literature.

Studies on chromium removal by rice husk carbon

Abstract: Le charbon active prepare par carbonisation d'enveloppe de riz avec l'acide sulfurique, suivie d'une activation au dioxyde carbone, elimine 88% du chrome dans les eaux usees

Determination of chromium(III) and chromium(VI) by ammonium pyrrolidinecarbodithioate-methyl isobutyl ketone furnace atomic absorption spectrometry

Abstract: The solution conditions and other parameters affecting the ammonium pyrrolidinecarbodithioate-methyl isobutyl ketone (APCD-MIBK) extraction system for the graphite furnace atomic absorption spectrometric determination of Cr(III) and Cr(VI) have been studied in detail. The parameters studied include pH of the aqueous phase prior to extraction, concentration of APDC, concentration of the potassium hydrogen phthalate buffer, the length of time needed for complete extraction, and the time-stability of the chelate in the organic phase. On the basis of these studies, procedures have been developed for the selective determination of Cr(VI), and the simultaneous determination of (Cr(III) + Cr(VI)) without the need to convert Cr(III) to Cr(VI). The value of Cr(III) is obtained by difference. The methods have been applied to the determination of Cr(III), Cr(VI), and (Cr(III) + Cr(VI)) in some natural and drinking water samples. The detection limits (3 standard deviations of blank) for Cr(III) and Cr(VI) are the same and found to be 0.3 ng/mL in the MIBK phase. Data are presented on accuracy, precision, and interference.

Fourier transform infrared studies of atomic titanium, vanadium, chromium, iron, cobalt, nickel and copper reactions with carbon dioxide in low-temperature matrices

Abstract: Titanium, vanadium, chromium, iron, cobalt, nickel, and copper metal atoms were cocondensed with CO/sub 2/ in neat matrices at 15 K. Even though a large proportion of atoms do not react, new complexes with CO/sub 2/ are characterized by using FTIR techniques and their infrared absorption bands are assigned. It is clearly shown that CO/sub 2/ is highly bent in these complexes. The behavior of oxophile metals is different from that of other metals which spontaneously form 1:1 complexes with CO/sub 2/. For Ti, V, and Cr, the authors observe first an insertion of metallic atom into a CO bond, leading to the formation of the intermediate (O)M(CO) molecule, followed by the CO/sub 2/ fixation on this complex, to form (O)M(CO)(CO/sub 2/). The other identified products in the matrices are CO, M(O), M(CO)/sub n/, and possibly a few carbonates. Most complexes are thermally unstable and decompose above 60 K. Only Fe and Ni compounds give rise upon annealing above 80 K to CO/sub 2/ reduction to CO along with the simultaneous formation of metal carbonyl complexes. Isotopic experiments with /sup 13/CO/sub 2/ and C/sup 18/O/sub 2/ allow them to conclude that the geometry of complexes is both metal and matrixmore » dependent: in neat CO/sub 2/ matrices, Fe and CO lead to a C coordination, the others being fixed in a side-on and end-on manner.« less

Production and uses of chromium

Abstract: Description d'ordre general de la production et de l'utilisation du chrome dans la vie courante

Chromium contamination of groundwater

Abstract: Etude de la mobilite du chrome dans les eaux souterraines. Cette mobilite depend de sa valence, de sa solubilite, de son adsorption sur le sol ou les materiaux en contact avec les eaux souterraines

Chromium in plants. Comparison between the concentration of chromium in Brazilian nonhypo and hypoglycemic plants.

Abstract: Chromium is an essential trace element and is associated with some biological pathways, especially with glucose tolerance. For these reasons, we decided to determine the concentration of chromium in two sets of Brazilian medicinal plants. The first group consisted of plants that are considered as antidiabetic, whereas the second included plants that do not have this therapeutic property. The concentration of chromium was determined by flameless atomic absorption. All the plants analyzed contain chromium in the normal range for this element, but the hypoglycemic plants contain more chromium than the others (1-4 micrograms/g compared to 0.5-1.5 micrograms/g).

The influence of ion-implanted yttrium on the selective oxidation of chromium in Co-25 wt.% Cr

Abstract: Specimens of Co-25 wt.% Cr, Co-25 wt.% Cr-1 wt.% Y, and yttriumimplanted Co-25 wt.% Cr alloy were oxidized at 1000°C in 1 atm O2. The implantation dosage ranged between 1016 to 1018 ions/cm2. The unimplanted binary alloy oxidized to a duplex Co-rich scale, but the Y-containing ternary alloy formed a continuous Cr2O3 layer. When the implantation dosages were lower than a nominal 1018 ions/cm2, the alloy failed to develop a similar continuous Cr2O3 layer as that observed with the Y-containing alloy. A temporarily stable external Cr2O3 scale was formed on the most heavily implanted specimen (1×1018 Y+/cm2). This Cr2O3 scale consisted of very fine-grained oxide, which is permeable to the outward transport of Cr and Co. Internal oxidation pretreatment of the ion-implanted specimens converting the Y metal to its oxide prior to the oxidation experiment, can enhance the development of an external Cr2O3 scale, but this scale is also unstable. Results suggest that the selective oxidation of chromium in an ordinarily non-Cr2O3 -forming alloy can be due to the reactive element oxides acting as preferential nucleation sites on the alloy surfaces, but the subsequent growth of these scales may require a continuous supply of reactive elements in the alloy.

Highly corrosion-resistant, surface-treated steel sheet

Abstract: A highly corrosion-resistant, surface-treated steel sheet which has in order a zinc or zinc alloy deposit as an undercoating deposit, a chromate coating, and a coating of resin composition comprising a base resin obtained by adding at least one basic nitrogen atom and at least two primary hydroxy groups to the terminal of an epoxy resin, silica, and a difficultly soluble chromium compound. This resin composition has predetermined weight ratios of base resin/silica, base resin/difficultly soluble chromium compound, base resin/(silica + difficultly soluble chromium compound), and silica/difficultly soluble compound. The coating of this resin composition may contain a polyisocyanate compound as a hardener and further a silane compound as a crosslinking agent between the base resin and silica.

Magnetic transitions in bcc vanadium, chromium, manganese, and iron.

Abstract: We have examined the transition from nonmagnetic to ferromagnetic behavior for elemental bcc vanadium, chromium, manganese, and iron by analyzing self-consistent parameter-free total-energy band-structure calculations in the local-spin-density approximation utilizing a fixed-spin-moment procedure. All systems are found to exhibit singular behavior and to undergo complex transitions as a function of volume. For each system, we find a set of critical Wigner-Seitz radii ${r}_{\mathrm{WS}}$ defining the onset of magnetic behavior and the end of nonmagnetic behavior. Vanadium and manganese exhibit composite (second-order and first-order) transitions with nonmagnetic low-spin and high-spin magnetic behavior. Chromium undergoes a first-order transition from nonmagnetic to magnetic behavior at expanded volumes, and iron undergoes a second-order transition and becomes nonmagnetic at reduced volumes.

Mitochondrial reduction of the carcinogen chromate: formation of chromium(V).

Abstract: Incubation of chromate with isolated rat liver mitochondria in vitro resulted in the uptake and reduction of chromium(VI), as well as the formation of chromium(V) species Chromate was rapidly taken up and reduced by intact mitochondria The rate of reduction of chromate by intact mitochondria was increased upon addition of succinate or malate plus glutamate, substrates for the electron-transport chain, but was decreased upon addition of cyanide, an inhibitor of the electron-transport chain Incubation of chromate with mitochondria in the presence or absence of malate, glutamate, and succinate resulted in a steady increase in the level of chromium(V) over time The extent of chromium(V) formation was increased upon addition of malate, glutamate, and succinate but was inhibited upon addition of the electron-transport chain inhibitors, antimycin, cyanide, or rotenone, to whole mitochondria High levels of glutamate plus malate inhibited chromium(V) formation; however, high concentrations of succinate or sulfate had no effect These studies suggest that the chromate-reductase activity in mitochondria is due to the electron-transport chain as well as other mitochondrial reducing systems which are insensitive to inhibitors of the electron-transport chain Since chromium(VI) is effectively metabolized by mitochondria in vitro and chromium(V) "reactive intermediates" are formed in the process, mitochondria may play a role in chromium(VI) carcinogenesis

Metal-polymer chemistry. II. Chromium-polyimide interface reactions and related organometallic chemistry

Abstract: We have studied the reactions occurring for the deposition of chromium onto pyromellitic dianhydride‐4,4’‐oxydianiline (PMDA‐ODA) polyimide for a wide range of metal coverages, using x‐ray photoelectron spectroscopy as well as solution studies of model compounds. A multistep, coverage‐dependent mechanism is proposed which includes an initial electron transfer from Cr to PMDA‐ODA, followed by formation of Cr–O and Cr–N polymer‐bound intermediates. At higher metal coverage, Cr–oxides and Cr–nitrides are formed which may activate the polymer for subsequent formation of Cr–carbide. In the course of this work we have shown that similarities exist between the chemistry of metal atoms in condensed phases and the reactions occurring between metal atoms and surfaces.