Showing papers on "Chromium published in 1986"

Spectroscopic, optical, and thermomechanical properties of neodymium- and chromium-doped gadolinium scandium gallium garnet

Abstract: Spectroscopic, optical, and thermomechanical properties of gadolinium scandium gallium garnet doped with trivalent neodymium and/or chromium are reported for use in the design of high-power solid-state lasers

Coloured coatings prepared by the sol-gel process

Abstract: Homogeneous clear transparent coloured coatings can be produced by using sol-gel processes. Transition metal elements are incorporated into the glass network as ions showing a certain valence and coordination. The oxidation-reduction equilibrium moves towards the oxidized state in these low temperature glassy films. It was found that cobalt exists as Co 2+ in tetrahedral coordination, chromium as Cr 6+ in tetrahedral symmetry and manganese as Mn 3+ in octahedral coordination. Crystalline segregations of Co 3 O 4 , Mn 2 O 3 , CuO and Cr 2 O 3 were also observed. The spectra for iron and copper coatings change with coating thickness. Both light scattering and absorption mechanism exist. These thin coating films give absorption colours which are too weak for application. Only colours due to light scattering (manganese, iron and copper ruby) were effective.

In vitro cytotoxicity of metals to bluegill (BF-2) cells.

Abstract: BF-2 cells, an established fibroblastic cell line derived from the caudal fin of bluegill sunfish (Lepomis macrochirus), were exposed to 18 metal salts. Cytotoxieity was assayed by the neutral red (NR) technique. Based on the concentration of metal that reduced the uptake of neutral red by 50% (NR50), the rank order of Cytotoxieity for the cationic metals was silver > mercury > cadmium > zinc > copper > cobalt > nickel > lead > tin > manganese > chromium (trivalent), and for the anionic metal complexes it was arsenite > dichromate > chromate > arsenate > selenite > permanganate > selenate. There was a strong correlation (r = 0.909) between the NR50 ranking for the divalent metal cations and their chemical softness parameters (σp). A good correlation (r=0.833) was also found between thein vitro NR50 Cytotoxieity values for the cationic metals and thein vivo water-borne LC50 values for bluegill. There was no correlation, however, between NR50 and LC50 data for the anionic metal complexes, primarily due to the unusual tolerance, as reported in the literature, of fish for hexavalent chromium salts.

Layered double hydroxides as supported anionic reagents. Halide-ion reactivity in zinc chromium hexahydroxide halide hydrates [Zn2Cr(OH)6X.nH2O] (X = Cl, I).

Abstract: Several new families of heterogeneous catalysts recently have been synthesized by intercalating metal ions and cationic metal complexes between the negatively charged layers of smectite clay A complementary class of layered compounds exist in which the charge on the layers and gallery ions is the reverse of that found for smectite clays. These are the layered double hydroxides (LDH's) of the type [M,\"M,\"'(OH)2(++V)]A,,,. Z H ~ O . ~ ~ The positively charged layers are brucitelike (MI(OH)~) with trivalent cations substituting for divalent cations in octahedral sites of the hydroxide sheet. Typically, the ratio y / x is in the range 0.20-0.50. In naturally occurring LDH minerals the interlayer anion A\"is most commonly carbonate as in hydrotalcite, Mg6A12(OH) 16(C03).4H20, and pyroaurite, M&Fe2(0H)16(C03). 4H20. However, a wide range of derivatives containing various combinations of MI', MI1', and A\" ions can be synthesized either by direct crystallization@ from aqueous solution or by anion exchangelo for A\" in a precrystallized host. LDH's have been investigated as solid ionic conductors\" and as catalyst p rec~rsors , '~J~ but the properties of the pristine compounds as supported anionic reagents or as catalysts for chemical synthesis have not been addressed. Unlike the galleries of smectites, which can be swelled by multiple layers of solvent to mimic a solution-like environment,' the galleries of LDH's accommodate only one or two layers of water and other polar molecules. This limitation in gallery swelling, along with the relatively high layer charge density, means that typical organic reagents are unable to penetrate the intracrystal space occupied by the anions. Here we demonstrate that although the gallery anions in a typical LDH are not accessible for direct intracrystalline reaction, they are readily transferred to external edge surfaces for reaction with substrates adsorbed at those sites. The reactions investigated were simple halide-exchange processes between the halide ions in Zn2Cr(OH)6X.H20 and alkyl halides in the condensed state (toluene) or in the vapor phase. The chloride form of the LDH was prepared by reaction of aqueous CrC13 with ZnO according to previously described p r o c e d ~ r e s . ~ ~ J ~

The fate of activë chromium hydroxide, Cr(OH)3•3H2O, in aqueous suspension. Study of the chemical changes involved in its aging

Abstract: L'hydroxyde de Cr actif se dissout instantanement dans les acides en formant Cr(OH 2 ) 6 3+ . L'acidification donne, apres precipitation ≥ 99,4% de Cr(OH 2 ) 6 3+ et ≤ 0,6% d'oligomeres Cr n (OH) 2 Op(aq) (3n−r−2p)+ . La proportion d'oligomeres croit non lineairement avec le temps et depend du pH

Reaction of chromium(VI) with thiols: pH dependence of chromium(VI) thio ester formation

Abstract: On etudie la reaction de substitution de coordinat du chrome VI avec cysteamine, cysteine, ester d'ethyle de cysteine homocysteine, acide mercapto-3 propionique, N-acetylcysteine et acide thioglycolique. La constante de vitesse apparente de formation des thioesters de chrome VI varie beaucoup avec le pH

Copper-chromium-polyimide composite

Abstract: A carrier for use in flexible circuits and tapeautomated- bonding includes a layer of vacuum deposited metallic chromium between the copper and polyimide. The chromium is vacuum deposited on the polyimide, affords resistance to undercutting from gold and tin plating baths, and allows conductor to be deposited on both sides of the polyimide.

Chromium(III)-doped pillared clays (PILC's)

Abstract: Une etude par spectrometrie de reflexion diffuse et par RPE est effectuee pour determiner l'environnement du Cr(III), le comportement catalytique variant selon la position de celui-ci

Process for trimerization

Abstract: A process for the trimerization of an olefin selected from the group consisting of ethylene, propylene, 1-butene, and mixtures thereof comprising passing the olefin in contact with a catalyst comprising the reaction product of (i) a chromium compound, which will provide active catalytic species under trimerization conditions; (ii) a hydrocarbyl aluminum hydrolyzed with about 0.8 to about 1.1 moles of water per mole of aluminum compound; and (iii) a donor ligand selected from the group consisting of hydrocarbyl isonitriles, amines, and ethers wherein the aluminum to chromium mole ratio is in the range of up to about 200 to one and the ligand to chromium mole ratio is in the range of up to about 100 to one.

Fe-Cr-C hardfacing alloys for high-temperature applications

Abstract: The microstructure and phase chemistry of a Fe-34Cr-4.5C wt% hardfacing alloy has been investigated using transmission electron microscopy and microanalytical techniques. The microstructure is found to consist of large primary M7C3. carbides in a eutectic mixture of austenite and more M7C3. The results indicate that the microstructure of the undiluted alloy becomes configurationally frozen at a temperature of about 1150° C during deposition by the manual metal arc welding technique. This allows the metastable austenite phase to contain a large chromium concentration (≈ 16 to 17 wt %), thus imparting good corrosion and oxidation resistance. Experimental data on the partitioning of chromium, manganese and silicon between the carbide phases are discussed in the context of the high-temperature stability of the alloy.

NaCl-induced accelerated oxidation of chromium

Abstract: This paper describes new phenomena about chloride-induced accelerated oxidation of chromium Thermal analysis was adopted to examine the oxidation, which was studied particularly in the case of NaCl The presence of NaCl remarkably accelerates the oxidation of chromium The process occurs below the melting point of NaCl, and the main reaction product is Cr2O3 In the accelerated oxidation NaCl plays a catalytic role because it is not consumed significantly in the process DTA analysis reveals that the heat of reaction also accelerates the rate of oxidation, especially at an early stage of the reaction The accelerated oxidation takes place similarly under the presence of chlorides other than NaCl, but the oxidation rate depends on the kind of salt Therefore the Cl− anion plays an important role in the process, while the nature of the cation affects the rate of acceleration

Deformation behaviour of retained β phase in β-eutectoid Ti―Cr alloys

Abstract: Plastic deformation mode and its relation to tensile properties were investigated in retainedβ phase ofβ-eutectoid type Ti-Cr alloys. A plate-like single variantω phase is induced during deformation of the most unstableβ phase having a minimum chromium content required to suppress martensitic transformation. A selected area electron diffraction pattern taken from a boundary region of the stress-inducedω phase plate can be explained by the idea that a single variant ofω phase is induced in a {3 3 2} 〈1 1 3〉 twin produced during deformation. Anisotropy in population of fourω phase variants decreases with increasing chromium content. On further increasing chromium content, deformation occurs by slip. Enhanced ductility is obtained in as-quenched Ti-Cr alloys accompanied byω phase transformation or {332} 〈1 1 3〉 twinning during deformation,ω phase of as-quenched Ti-Cr alloys changes continuously from commensurate structure with sharp reflections to incommensurate structure with diffuse reflections with increasing chromium content. The obtained results inβ-eutectoid type Ti-Cr alloys are quite similar to those inβ-isomorphous type Ti-V alloys.