Chromium parameters

Table 6. Operating Parameters for Electrowinning of Chromium from Chrome Alum...

Table 8. Chemical Composition and Operating Parameters for Chromium Electroplating Baths...

Oxyfluoroniobates, M2Nb05F, containing trivalent metals (where M = Ti, V, Cr) have the same type of structure [264], except for Cr2Nb05F, which has a tri-rutile type structure. This exception is related to the ordered, rather than statistical, distribution of chromium and niobium cations in the oxyfluoride octahedrons, which leads to a corresponding increase in cell parameter c. 

It is evident [see Eq. (5), Section II[] that for catalysts of the same or similar composition the number of active centers determined must be consistent with the catalytic activity it can be expected that only in the case of highly active supported catalysts a considerable part of the surface transition metal ions will act as propagation centers. However, the results published by different authors for chromium oxide catalysts are hardly comparable, as the polymerization parameters as a rule were very different, and the absolute polymerization rate was not reported. 

Rate law flooding. The second-order rate constant for the reaction between the hydrated ions of vanadium(3+) and chromium(2+) depends on [H+ ]. From the data given, which refer to T = 25.0 °C and a constant ionic strength of 0.500 M, formulate a two-parameter equation that describes the functional dependence. Evaluate the two constants. Compare your result to the one derived in to Problem 1 -2. 

Chromium is reported17 also to have a modification with the A12 structure, for which, however, parameter values have not been determined. 

U.S. Code of Federal Register 40CFR-Chapter I, Part 467, p. 615, Aluminum Forming Point Source Category, available at http //www.access.gpo.gov.5 Table 5.19 indicates that the regulated parameters for pretreatment of aluminum forming industrial wastewater are chromium, cyanide, zinc, and total toxic organics (TTO). 

The use of aluminum-based masks in photolithography has been proposed.347 According to the scheme employed, aluminum is deposited onto a polished glass sheet. The regions of the mask that should be light transparent are then converted into porous oxide. As the operation of aluminum anodization exhibits a much better vertical anisotropy than chemical etching, the masks obtained reproduce the parameters of standard masks more precisely than the chromium masks usually used. 

Chromium zeolites are recognised to possess, at least at the laboratory scale, notable catalytic properties like in ethylene polymerization, oxidation of hydrocarbons, cracking of cumene, disproportionation of n-heptane, and thermolysis of H20 [ 1 ]. Several factors may have an effect on the catalytic activity of the chromium catalysts, such as the oxidation state, the structure (amorphous or crystalline, mono/di-chromate or polychromates, oxides, etc.) and the interaction of the chromium species with the support which depends essentially on the catalysts preparation method. They are ruled principally by several parameters such as the metal loading, the support characteristics, and the nature of the post-treatment (calcination, reduction, etc.). The nature of metal precursor is a parameter which can affect the predominance of chromium species in zeolite. In the case of solid-state exchange, the exchange process initially takes place at the solid- solid interface between the precursor salt and zeolite grains, and the success of the exchange depends on the type of interactions developed [2]. The aim of this work is to study the effect of the chromium precursor on the physicochemical properties of chromium loaded ZSM-5 catalysts and their catalytic performance in ethylene ammoxidation to acetonitrile. 

A review of recent advances in chromium chemistry (82) supplements earlier comprehensive reviews of kinetics and mechanisms of substitution in chromium(III) complexes (83). This recent review tabulates kinetic parameters for base hydrolysis of some Cr(III) complexes, mentions mechanisms of formation of polynuclear Cr(III) species, and discusses current views on the question of the mechanism(s) of such reactions. It seems that both CB (conjugate base) and SVj2 mechanisms operate, depending on the situation. The important role played by ionpairing in base hydrolysis of macrocyclic complexes of chromium(III) has been stressed. This is evidenced by the observed order, greater... 

Kinetic parameters for aquation at corresponding Cr(III) and Co(III) complexes have been compared for a series of complexes cis-[ML4XY]"+, where L4 = (NH3)4 or (en)2, X = Cl- or H20, and Y=an uncharged leaving group (DMSO, DMF, or DMAC). The uniformly negative activation volumes (AV between —2 and —11 cm3 mol-1) for the chromium complexes contrast with uniformly positive activation volumes (A V between +3 and +12 cm3 mol-1) for the cobalt complexes - AV values provide a more clear-cut contrast than AS values here (22). 

In all 28 parameters were individually mapped alkalinity, aluminum, antimony, arsenic, barium, boron, bromide, cadmium, calcium, chloride, chromium, conductivity, copper, fluoride, hardness, iron, lead, magnesium, manganese, nitrate, pH, potassium, selenium, sodium, sulphate, thallium, uranium, and zinc. These parameters constitute the standard inorganic analysis conducted at the DENV Analytical Services Laboratory. 

A number of different chromium collectors were also examined, including R84, which is a sulphonate collector as the primary collector, and amine acetate as the secondary collector was found to be effective for chromium flotation. The most critical parameter for selective chromium flotation was the pH. Selective chromium flotation occurs at a very narrow pH region, 1-2.5. Figure 25.12 shows the effect of pH on chromium flotation. 

The general approach is illustrated in detail for the case of aqueous ferrous and ferric ions, and the calculated rate constant and activation parameters are found to be in good agreement with the available experimental data. The formalisms we have employed in studying such complicated condensed phase processes necessarily rely on numerous approximations. Furthermore, some empirical data have been used in characterizing the solvated ions. We emphasize, nevertheless, that (1) none of the parameters were obtained from kinetic data, and (2) this is, as far as we are aware, the first such theoretical determination to be based on fully Ab initio electronic matrix elements, obtained from large scale molecular orbital (MO) calculations. A molecular orbital study of the analogous hexaaquo chromium system has been carried out by Hush, but the calculations were of an approximate, semi-empirical nature, based in part on experi-... 

Table 16.1 Characteristics of the investigated soils and parameters affecting redox of chromium TOC total organic carbon, SOM soluble organic matter. Reprinted with permission from Kozuh N, Stupar 1, Gorenc B (2000) Reduction and oxidation processes of chromium in soils. Environ Sci Technol 34 112-119. Copyright 2000 American Chemical Society...

Mattioli G. S. and Bishop F. (1984). Experimental determination of chromium-aluminum mixing parameter in garnet. Geochim. Cosmochim. Acta, 48 1367-1371. 

At pH 7.0, the 39/Cr(VI) reaction mixture leads to detectable oxo-Cr(V) complexes giving room-temperature EPR parameters that may match a coordination of the chromium center to a diol group, leading to the structures suggested in Scheme 14.108 Note that these assignments should be verified with more detailed EPR and DFT studies. 

A2g transitions, respectively. Besides being able to correlate jS with oscillator strength,/, of transitions the values may be employed 42) to evaluate the effective charges on the Cr(III) ions in various complexes. Fig. 4 provides plots of the effective metal charge vs. /3, the nephelauxetic parameter and B, the Racah interelectronic repulsion parameter for chromium(III). Jorgensen... 

Fig. 4. Effective metal charge, Z, in chromium(III) complexes as a function of the nephel-auxetic parameter, P, and the Racah interelectronic repulsion parameter, B...

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