Systemic chromium

Al—Cr. Although no commercial ahoys are based on this system, chromium [7440-47-3] Cr, is an ingredient of several complex and commercially significant ahoys (Fig. 16. The Cr is added for control of grain stmcture. The Al—Cr system has a peritectic portion at 661°C where soHd solubiHty is 0.7% Cr and Hquid solubiHty is 0.4% Cr. Free2ing of binary ahoys containing >0.4% Cr produces coarse primary crystals (metallic inclusions) of AlyCr [12005-37-7] which may adversely affect mechanical properties. In complex ahoys, the Hquid solubiHty can be reduced such that formation of primary AlyCr crystals may occur at significantly lower Cr contents. 

The Binary System Chromium-Boron. I. Phase Analysis and Structure... 

DR. THOMAS MEYER (University of North Carolina) I feel that you have glossed over something that is actually very interesting, and that is the whole question of the Bronsted relationship. You have now observed a large number of systems, chromium, molybdenum, tungsten, which exhibit tricarbonyl anions. Have you looked at rate constants for all those species with the same hydride You would then have three bases, all with identical structures. 

Recently a fairly inexpensive way of high-temperature experimentation has been found to investigate refractory sulfides and related multicomponent systems up to temperatures of nearly 2000 °C using resistance furnaces. These techniques are discussed below and applied to some sulfide systems, in particular of those metals which belong to the VI-B group. The binary systems chromium-sulfur, molybdenum-sulfur, tungsten-sulfur, as well as some other ternary and quaternary systems and their reactions are reviewed and completed within the limits of the new experimental procedure. 

Hawaii (cont.) MCL applicable to all public water systems—chromium 0.1 mg/L HI Dept Health 1999b... 

Gad SC. 1989. Acute and chronic systemic chromium toxicity. Sci Total Environ 86 149-157. 

We have considered ceramic synthesis in an open crucible and closed glass tube. A third possibility is a flow system. Chromium chloride, CrCl3, can be prepared by passing carbon tetrachloride over a sample of chromium oxide maintained at 900°C (Angelici, 1986) ... 

It is immediately apparent from Fig. 20-1 that along the one symmetry line in the Brillouin Zone shown, there are two or three bands crossing the Fermi energy for each metal and therefore quite a complex set of Fermi surfaces. These have been thoroughly studied, using the techniques discussed in connection with simple metals. It would, however, be quite inappropriate here to attempt any complete discussion of this problem, Instead, the Fermi surface of a single system, chromium, will be discussed. It is perhaps the most interesting case, and it illustrates the principal effects that enter considerations of the other systems. We shall then turn to the density of states, which dominates many of the electronic properties. 

See also Cardiovascular System Chromium Hexavalent Compounds Metals Respiratory Tract. 

The compounds CrSe(cr), Cr3Se4(cr) and Cr2Se3(cr) have been reported in the system chromium-selenium. Cr2Se3(cr) exists in two modifications the low-temperature y phase, which is stable up to 1084 K and the high-temperature a phase. Experimental thermodynamic information is only available for the two polymorphs of Cr2Se3(cr). 

The results show a significant improvement of the catalytic activity for the studied ssubstances. After verification by long term activity tests and real size experiments, may be applicable in practice. The procedure is simple and does not require the removal of the T.W.C. from the exhaust system. The acetic acid solution could be pumped through the exhaust system using the dissmantled gas iidet and outlet. The highly corrosive resistant construction of the exhaust system (chromium steel) is not expected to be attacked by the weak acetic acid. 

More closely related to kinetics and mechanism are three reviews from Danish chemists, one on the state of the art with respect to Cr(III) substitution reactions and the other two ° survey /t-diol dinuclear Cr(III) systems. Chromium chemistry is also discussed in a general review on metal-ion-assisted aquation reactions " and in a review on the effect of pressure on reaction rates. In the following sections, units for and AH are in kJ mol A5 in J K mol A V in cm mol visible absorption spectral maxima (A ax) in nm, and molar extinction coefficients (e) in cm Unless otherwise stated, all rate constants are reported at 25.0 (298.2 K). 

Put] Putman, J.W., Potter, R.D., Grant, N.J., The Ternary System Chromium-Molybdenum-Iron , Trans. Amer. Soc Met., 43, 824-845 (1951) (Crys. Straeture, Morphology, Phase Diagram, Experimental, 14)... 

Kur] Kumakov, N.N., Investigation of the System Chromium-Silieon-Iron in the Region of Sili-... 

Liquid-phase oxidation is carried out predominantly in the acetic acid/ Co /Br system chromium oxidation is also used. In the predominant reaction of p-xylene to terephthalic acid, which takes place in two stages via methylbenz-aldehyde, the following rate equation is valid for the first stage of the process ... 

The strong interactions with metal ions extend to the use of metal-modified electrodes in electrocatalysis. Catalysis has been demonstrated with four systems. Chromium treatment results in as much as a 200 mV positive shift in the reduction peak for lO in acetate buffer This has been compared to the necessity for prior oxidation of the platinum electrode surface Ruthenium pretreatment of (SN), electrodes results in a catalytic current for the I / couple in phosphate buffer, pH 7.6. These electrodes also photoelectrochemically reduce protons to hydrogen at —0.05 V versus SCE in dilute sulfuric acid solution Molybdate treated electrodes have been used to electrochemically reduce acetylene at potentials of 1.5 V versus SCE in borate and hydroxide solutions. Iron treated electrodes show some ability to facilitate this reaction, but the rate is slower than with the molybdate treated electrodes... 

Under this system chromium(II) oxide is named chromous oxide. We do not use this older system in this text. 

Molybdenum(ni).—comparison of recent results for the anation of the [Mo(HaO) ion with results for analogous studies of other inert metal ions of the type [M(HaO)6] is made in Table 21. A comparison of the d systems chromium(m)... 

A significant drawback of the early NHK reactions was that they were performed using stoichiometric amounts of chro-mium(II) chloride. Because chromium(II) is a one-electron donor, a large excess of toxic chromium(II) salts was required. This difficulty was overcome, and the synthetic utility of the reaction greatly enhanced by Fiirstner and shi s development of a catalytic redox process. In this system, chromium(II) is recycled from chromium(III), which allows for much reduced quantities of chromium salts, thereby rendering the reaction more environmentally benign. ... 

Por] Portnoy, K.I., Romashov, V.M., Romanovich, I.V., The Phase Diagram of the System Chromium-Boron (in Russian), Poroshk. Metall, (4), 51-57 (1969) (Phase Diagram, Experimental,, 19)... 

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