Chromium sources

Shiau, S.Y. and M.J. Chen. 1993. Carbohydrate utilization by tilapia (Oreochromis niloticus X O. aureus) as influenced by different chromium sources. Jour. Nutr. 123 1747-1753. 

Ghosh S, Sharma AD, Basu RN, and Maiti HS. Synthesis of La07Ca03CrO3 SOFC interconnect using a chromium source. Electrochem. Solid-State Lett. 2006 9 A516-A519. 

Most catalysts are based on chromium that has been studied for this purpose since the mid-seventies, probably started by Union Carbide Corporation. Chromium is the metal of the Phillips ethene polymensation catalysts and presumably it was discovered accidentally that under certain conditions 1-hexene was obtained as a substantial by-product. Neither the precise catalytic cycle nor the intermediate complexes or precursors are known. It is generally accepted that an alkyl aluminium compound first reduces the chromium source and that coordination of two molecules of ethene is followed by cyclometallation, giving a chromocyclopentane. During the cyclometallation the valence of chromium goes up by two and thus a starting valence of either one or zero seems reasonable. This cyclic mechanism explains why such high selectivity is obtained [5],... 

Fig. 23. Effect of dehydration temperature on the MBssbauer spectrum of Fe2+-M. (a) 15 Torr of H20, 273 K. (b) evacuated 24 hr, 273 K (c) evacuated 3 hr, 517 K (d) evacuated 8 hr, 800 K (e) 15 Torr of H20, 273 K. All spectra at room temperature and on the same sample. Zero velocity is with respect to a 57Co in chromium source. Figure according to Garten et cd.

Fig. 24. Effect of degree of hydration on the Mdssbauer spectrum of an ion exchange resin containing iron. Water concentration (1) 0, (2) 0.22, (3) 1.24, (4) 2.93, (5)4.5, (6) 6 HzO molecules per sulfonic acid group. Zero velocity is with respect to a 57Co in chromium source. Figure according to Gol danskii et al. (187).

K, re uce 2, - chromium source. Figure according to Garten and Ollis... 

X-Ray diffraction powder patterns were developed by using a chromium source and a Phillips Debye-Sherrer camera. Due to their small size, the samples from the back of the halberd were irradiated for 12.5 h, and the green pseudomorph sample for 12.3 h. The black pseudomorph sample, larger, was irradiated for only 5 h. The exposed film was measured in accordance with standard procedures (8) and the resulting diffraction spacing values were compared to standard values of known materials (9). 

Synonyms Cr(acac-Br)3 Tris(3-bromopentane-2,4-dionato)chromium Source Lagalante, A. F Flansen, B. N. Bruno, T. J. Sievers, R. E.Inorg. Chem. 995), 34(23), 5781-5785. 

Synonyms c/s-Cr(tfa)3 c/s-Tris(1,1,1-trifluoropentane-2,4-dionato)chromium Source Lagalante, A.F. Hansen, B.N. Bruno,T. 

Organic sources of Cr(VI) have also been investigated as the chromium source. Baker and Carrick [148] first investigated bis(triphenylsilyl) chromate as a homogeneous model for the surface chromate structures postulated to exist on the Phillips catalyst. This chromate ester is quite stable, but like Cr(VI) /silica, it can also be reduced by olefins under polymerization conditions to give the corresponding aldehyde and Cr(II) or Cr(III). Thus, it mimics the behavior of Cr(VI)/silica in many respects [149]. Bis(triphenylsilyl) chromate does catalyze ethylene polymerization,... 

The chromium compound can be impregnated onto the carrier by use of any anhydrous, aprotic solvent. The chromium source can be a hex-avalent chromium compound, such as bis(f-butyl) chromate in pentane,... 

A novel method has been developed for hydrothermal synthesis of zeolite beta with high chromium content and low aluminum content under static conditions. The crystalline phase and spectroscopic property of this material were characterized by means of XRD, XRF, IR, UV-Vis DRS, ESR and SEM. The results revealed that part of the chromium ions were incorporated into the zeolite framework during crystallization. Using tris(acetylacetonato) chromium(III), [Cr(C5H702)3], as a chromium source, Cr/Si molar ratio can be up to 1/48 in the calcined and ion-exchanged sample. The chromium aluminosilicate exhibited a high oxidative activity in the presence of dilute H2O2. 

Ferrochromium is an alloy of iron and chromium. More than 80% of all chromite ore is consumed in manufacturing this alloy. It is mainly used as the chromium source for the manufacture of stainless steels and other chromium steels. HC ferrochromium with high carbon content (5-6%) is manufactured in electric furnaces with coke as the reducing agent. The process has a high energy consumption, 4000 kWh per tonne of chromium metal. Plants for ferrochromium production have therefore been located in areas with low energy prices. This was one reason why Sweden, without its own chromium deposits, was a pioneer country in this field and in the production of stainless steels. 

The Phillips catalyst is prepared by impregnating a chromium compoxmd into a high surface area silica, such as Davison Grade 952 silica, with a pore volume of about 1.6 cc/g and a surface area of about 300 mVg. The type of chromium compound used as the chromium source does not affect the behavior of the finished catalyst after the activation (oxidation) step [4]. Chromium(III) acetate, ammonium chromate or dichromate and chromium oxide (CrOj) are possible sources of chromium. Sufficient chromium is used to yield about 0.5 tol.O wt% Cr in the final catalyst. 

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