Showing papers on "Chromium published in 1973"

X-Ray photoelectron spectroscopy of chromium–oxygen systems

Abstract: X-Ray photoelectron spectroscopy has been used to study a series of chromium–oxygen compounds. It has been shown that the ionisation energy of the chromium 2p electrons is dependent primarily on the oxidation state of the chromium metal ion, but that small perturbations may be attributed to changes in crystal structure and hence the Madelung potential. Multiplet splitting in chromium(III) compounds contributes to peak widths, and the chemisorption of water and oxygen has a marked effect on the observed peak profiles. In addition such chemisorption apparently contributes to the build up of surface charge, thereby complicating the precise determination of binding energies.

Thermodynamics of carbon in nickel, iron-nickel and iron-chromium-nickel alloys

Abstract: Iron-nickel alloys with 8 and 16 wt pct nickel and iron-chromium-nickel alloys with 8 pct nickel and chromium contents in the range of 2 to 22 pct were equilibrated with iron and nickel in flowing CH4-H2 gas mixtures and in sealed capsules under partial vacuum at temperatures between 700 and 1060°C. Carbon activities in these alloys were established from the carbon concentrations in the nickel by applying Henry’s law to the solubility of carbon in nickel that was determined in the temperature range of 500 to 1000°C. First-order free-energy interaction parameters were used to relate the carbon activities to composition and temperature in the single-phase austenitic Fe-Ni and Fe-Cr-Ni alloys. An expression was also developed to evaluate carbon activities in Fe-Cr-Ni alloys in the region of higher chromium contents (〉4 wt pct) that result in a two-phase austenite plus carbide mixture at these temperatures.

Heavy metal toxicities: levels of nickel, cobalt and chromium in the soil and plants associated with visual symptoms and variation in growth of an oat crop

Abstract: A study was made of toxicity in a field crop of oats on a soil developed in an area where ultrabasic rocks occur. An area selected for sampling showed a range of toxicity from the border where plants were normal to the centre where plants were most affected. The total nickel, cobalt, and chromium contents of the soil increased to high levels at the centre of the area. The concentration of the elements in soil solutions extracted with a centrfuge from soils at field capacity were in the order nickel > cobalt > chromium, the order in which they are found in natural waters. In the soil solutions nickel ranged from 0.13 to 3.25 p.p.m., cobalt from 0.03 to 0.14p.p.m., and chromium from 0.01 to 0.02p.p.m. The concentrations found in the soil solutions were compared with concentrations known to induce toxicities in oats grown in frequently renewed solution cultures. These comparisons indicated that the nickel ranged up to levels which were definitely toxic. At its highest level cobalt was present at less than one-tenth of the level needed to induce toxicity, while chromium was present at only one-hundredth of the minimum level for toxicity. Analyses of the toys of plants from the centre of the area indicated values of chromium which would be considered toxic, but because of the very low concentrations of chromium in the soil solutions it was considered more likely that the chromium detected was in soil material which the acid detergent washing procedure failed to remove. Evidence presented indicates the particular importance of contamination in the case of chromium. Nickel was present in much higher quantities at toxic levels. Cobalt was below toxic levels. The symptoms observed in the field and symptoms induced by the application of nickel to oats in pot cultures are described. A feature of these symptoms was a regular succession of chlorotic bands. The evidence suggested that the banding pattern, which is best developed in clear weather, relates to the changing conditions which influence the actively growing tissue as the leaf is emerging. The symptom provided us with a means of identifying nickel toxicity in the field. Degrees of toxicity were related to levels of elements in soil extracts and in the plants.

Olefin polymerization catalyst

Abstract: A method for preparing a composition of matter comprising silica and titanium, convertible to a catalyst suitable for olefin polymerization by the addition of chromium and the process performable therewith, the preparation involving adding an alkali metal silicate to an acid containing a titanium compound, and recovering a dry gel for use as a polymerization catalyst upon the addition of chromium.

Crack propagation under creep conditions in a quenched % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXafv3ySLgzGmvETj2BSbqefm0B1jxALjhiov2D% aebbfv3ySLgzGueE0jxyaibaiGc9yrFr0xXdbba91rFfpec8Eeeu0x% Xdbba9frFj0-OqFfea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs% 0dXdbPYxe9vr0-vr0-vqpWqaaeaabiGaciaacaqabeaadaqaaqGaaO% qaaiaaikdadaWcbaWcbaGaaGymaaqaaiaaisdaaaaaaa!3E80!\[2\tfrac{1}{4}\]chromium 1 molybdenum steel

Abstract: Crack growth rates have been measured in single edge-notched specimens of % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXafv3ySLgzGmvETj2BSbqefm0B1jxALjhiov2D% aebbfv3ySLgzGueE0jxyaibaiGc9yrFr0xXdbba91rFfpec8Eeeu0x% Xdbba9frFj0-OqFfea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs% 0dXdbPYxe9vr0-vr0-vqpWqaaeaabiGaciaacaqabeaadaqaaqGaaO% qaaiaaikdadaWcbaWcbaGaaGymaaqaaiaaisdaaaaaaa!3E80!\[2\tfrac{1}{4}\]Cr 1 Mo steel loaded in tension at 565 dgC. It is shown that the creep crack growth rate in tests of up to about 2,000 hours duration can be described in terms of the sharp crack stress intensity factor. A correlation is obtained over five orders of magnitude in crack growth rate and the relationship of these results to conventional creep tests is discussed. For the particular test conditions the time required to initiate a crack from a notch is not significant compared with the total times for specimens to fail. Under some conditions high rates of stable crack growth rate can be obtained. The work has obvious potential in the assessment of the integrity of components which contain defects and operate under creep conditions. A possible application of the data to the analysis of a particular thermal fatigue situation is suggested.

Chromium in foods in relation to biological activity.

Abstract: Chromium was determined in foods and in extracts of selected samples of foods using modification of the colorimetric procedure to stabilize color development. Extracts were prepared both by hydrolysis of samples to obtain total chromium and by alcohol extraction. Biological activities of these extracts were determined using the glucose oxidation procedure in the presence of insulin. No significant relationship was found between total chromium and biological activity. However, there was a significant relationship for chromium in alcohol extracts of meats, fungi, seeds, and seafoods, excluding fruits and vegetables. A proposed evaluation of the foods was based on these data.

Übergangsmetall‐Carben‐Komplexe, LIV. Synthese von übergangsmetall‐carbonyl‐ylid‐Komplexen aus übergangsmetall‐carbonyl‐carben‐Komplexen

Abstract: Durch Umsetzung sekundarer und tertiarer Alkylphosphine PX3 [X3 = (CH3)3, (C2H5)3, (n-C4H9)3, (CH3)2H] mit den (Alkoxycarben)- bzw. (Alkylthiocarben)pentacarbonyl-Komplexen von Chrom(0) und Wolfram(0), (CO)5Cr[C(OCH3)C6H5], (CO)5W[C(OCH3)CH3] und (CO)5W[C(SCH3)CH3], bei tiefen Temperaturen wurden unter Addition der Phosphine an das Carbenkohlenstoffatom entsprechende Ylid-pentacarbonylmetall-Komplexe (CO)5 M[C(PX3) (YCH3)(Z)] (M = Cr, W; Y = O, S; Z = CH3, C6H5) erhalten. Die Strukturen der schwach gelblichen, diamagnetischen, z T. sehr thermolabilen Verbindungen wurden durch Analyse, IR-, NMR- und Massenspektren gesichert. Die partielle thermische Reaktion von (CO)5Cr[C(P(CH3)2H)(OCH3)(C6H5)] in Aceton zu (CO)5Cr{P(CH3)2[CH(OCH3)(C6H5)]} wurde nachgewiesen. Transition Metal Carbene Complexes, LIV. Synthesis of Transition Metal Carbonyl Ylide Complexes from Transition Metal Carbonyl Carbene Complexes Secondary und tertiary alkylphosphines PX3 [X3 = (CH3)3, (C2H5)3, (n-C4H9)3, (CH3)2H] react with (alkoxycarbene)- or (alkylthiocarbene)pentacarbonyl complexes of chromium(0) and tungsten(0),(CO)5Cr[C(OCH3)C6H5], (CO)5W[C(OCH3)CH3] and (CO)5W[C(SCH3)CH3], at low temperatures to give the corresponding ylidepentacarbonylmetal complexes (CO)5M[C(PX3)(YCH3)(Z)] (M = Cr, W; Y = O, S; Z = CH3, C6H5) under addition of the phosphines to the carbene carbon atom. The structures of the pale yellow, diamagnetic, and partially very thermolabile compounds were established by analysis, i.r., n.m.r., and mass spectra. The partial thermal conversion of (CO)5Cr[C(P(CH3)2H)(OCH3)(C6H5)] in acetone was shown to yield (CO)5Cr{P(CH3)2[CH(OCH3)(C6H5)]}.

Thermodynamic properties of solid alloys of chromium with nickel and iron

Abstract: The thermodynamic properties of chromium have been determined in the Ni-Cr and Fe-Cr binary systems and in the Fe-corner of the Fe-Ni-Cr system. These properties are based on experimental measurements using solid oxide electrolyte cells of the type: Cr, Cr2O3 I ThO2-Y2O3Cr (alloy), Cr2O3. In the Ni-Cr system, between 900 and 1300°, the activity of chromium exhibits negative deviation from ideality up to about 25 at. pct chromium. For alloys higher in chromium content, the activity of chromium exhibits positive deviation from ideality. In the Fe-Cr system, between 900 and 1200°, and 0 and 63 at. pct Cr, the chromium activity when referred to solid pure chromium exhibits positive deviation from ideality in both the γ and α phases, approaching ideality with increasing temperature. The nickel and iron activities in these two respective binary systems were calculated by a Gibbs-Duhem integration. The activity of chromium, referred to solid pure chromium, was measured between 900 and 1200° in solid Fe-Ni-Cr alloys with chromium concentrations of 9, 20, and 30 at. pct and Ni concentrations of 8, 18, and 30 at. pct. Additions of nickel to Fe-Cr alloys in the above concentration range are found to increase the chromium activity. The effect of nickel in increasing the chromium activity is greater at both greater chromium contents and lower temperatures.

Cathodic treatment of chromium-plated surfaces

Abstract: A method for treating a chromium-plated surface is provided characterized by the fact that a chromium-plated article is dipped as the cathode in a water-soluble or water-dispersible resin solution or dispersion prepared by diluting with water a resin salt of at least one synthetic polyamino resin with a water-soluble organic acid and/or a water-soluble inorganic acid, and then passing a direct current in the range of 10 - 300 volts through the aqueous bath so that there is formed a resin film on the chromium plated surface the chromium-plated surface is pretreated prior to the resin coating step by anodization in aqueous chromate solution or by heat treatment so that the surface electrode potential is greater than -0.42 volts.

The distribution of chromium between ferrite and austenite and the thermodynamics of the α/γ equilibrium in the Fe-Cr and Fe-Mn Systems

Abstract: New measurements of the α/γ equilibrium in the Fe-Cr system are presented and all the relevant experimental information now available, including thermodynamic data, is evaluated using a regular solution model. The two-phase field is calculated in good agreement with most of the experimental measurements. The point of minimum is obtained at 1119 K and 7.0 at. pct Cr (6.6 wt pct Cr) and the maximum solubility in austenite is 11.9 at. pct Cr (11.2 wt pct Cr). The thermodynamic quantities describing the effect of chromium on the relative stability of ferrite and austenite are similar to those for manganese. The comparison is based upon a new evaluation of the Fe-Mn system. In particular, low chromium contents are found to have a stabilizing effect on austenite up to a temperature of 1675 K.

Precipitation of Chromium in Copper and Copper-Nickel Base Alloys

Abstract: The precipitation of chromium-rich particles in Cu-Cr and Cu-Ni-Cr alloys has been studied by electron microscopy, electrical resistivity measurements and tensile testing. The results show that chromium precipitate has an fcc structure and the bcc structure previously proposed was not observed. A strong tendency for alignment of adjacent precipitates was observed in the ternary alloy but preferential precipitation on dislocations and grain boundaries showed that this was not due to spinodal decomposition. An alternative explanation based on elastic interactions is discussed. The resistivity results on the binary alloy shows no anomalous peaks in the early stages and were analyzed by the Avrami or Johnson-Mehl method to give the parametern = 1.5 and activation energy for growth of ~1.35 eV.

µ3-Oxotrimetal acetato-complexes of chromium, manganese, iron, cobalt, rhodium, and iridium

Abstract: New pyridine- and β-picoline-containing oxo-centred complex ions [M3IIIO(CO2Me)6L3]+, M = Cr, Mn, Fe, Co, Rh, and Ir, L = py and β-pic, were synthesised and their redox behaviour studied electrochemically. There is evidence for reduced species in which the oxo-centred triangular structure is maintained in the case of the Mn, Fe, and Co complexes but these could not be isolated. For iridium, complexes [Ir3III,III,IVO(CO2Me)6L3]+2 in which the metal atom is in the mean oxidation state 3⅓ have also been characterised and shown to undergo reduction to the IrIII species. Attempts to prepare oxo-centred complexes of Cu, Ag, Ni, Pd, Pt, and Mo were unsuccessful. The cobalt complex ion [Co3O(CO2Me)6L3]+ appears to be different from the other oxo-centred ions and a structure with both bridging and chelate acetato-groups is proposed.

The concentration-dependent diffusion of chromium in nickel oxide

Abstract: A theory has been developed to describe the diffusion of trivalent impurities in a divalent metal oxide and has been evaluated for the diffusion of trivalent chromium in NiO. The theoretical model developed by Lidiard to describe the diffusion of divalent impurities in alkali halides was revised to describe the migration of chromium-vacancy complexes in the divalent NiO crystal. A radioactive51Cr tracer and NiO single crystals were used and the concentration profiles were analyzed by sectioning and counting. The diffusion coefficient of chromium as a function of chromium concentration was determined at 1000°, 1100°, 1200°, and 1300°C and at oxygen pressures of 1.0, 10-2, and 10-5 atm using a modified Matano analysis of the concentration profiles. A reasonable fit of the theory to the experimental concentration dependence of chromium diffusion was obtained which indicates that, at 1000°C and above, chromium diffuses in NiO by a mechanism involving chromiumvacancy two-member complexes. The energy of association of a chromium-vacancy couple was found to increase from approximately -3000 cal at 1000°C to about -600 cal at 1300°C. The diffusivity of chromium (Dcr) in NiO saturated with chromium increases from approximately 2 x 10-12 cm2/s at 1000°C to 2 x 10-10 cm2/s at 1300°C.

Carbon-13 nuclear magnetic resonance spectra of some carbonyl complexes of chromium, molybdenum, and tungsten

Abstract: 13 C N.m.r. spectra and some i.r. (carbonyl) stretching frequencies of the complexes [M(CO)6], [W(CO)nL6–n], [M′(CO)4(norbornadiene)], and [M(CO)3L′][M = Cr, Mo, or W; M′= Cr or Mo; and n= 1, 2, or 3; L = PEt3 and P(OMe)3, and n= 1; L′= mesitylene, 1,2,4,5-tetramethylbenzene, hexamethyibenzene, or cyclo-hepta-1,3,5-triene] are reported. The work includes the first reported measurement of 1J(95Mo–13C).

Electrochemical contaminant removal from aqueous media

Abstract: Contaminating ions are removed from an aqueous medium, e.g., hexavalent chromium ions from cooling tower waters, by an electrochemical method which includes formation of an insoluble iron compound or complex of the contaminant ion, utilizing an anode of iron, iron alloy or insoluble iron compound. The hexavalent chromium contaminant, as chromate or dichromate, is changed to trivalent chromium, a less toxic form. The method is applicable to the removal of other contaminant ions, e.g., cyanide, which also converts to less toxic form. Also described are electrolytic cells and apparatuses useful in effecting the method.