Chromium oxide conductivity

The equilibrium is more favorable to acetone at higher temperatures. At 325°C 97% conversion is theoretically possible. The kinetics of the reaction has been studied (23). A large number of catalysts have been investigated, including copper, silver, platinum, and palladium metals, as well as sulfides of transition metals of groups 4, 5, and 6 of the periodic table. These catalysts are made with inert supports and are used at 400—600°C (24). Lower temperature reactions (315—482°C) have been successhiUy conducted using 2inc oxide-zirconium oxide combinations (25), and combinations of copper-chromium oxide and of copper and silicon dioxide (26). 

The shift reaction can be conducted in a second reactor, catalyzed by a mixture of iron and chromium oxides. The product of reforming is known as synthesis gas, or syngas, and is mostly used in the manufacture of ammonia and methanol. One of the earliest steam reforming processes was developed in Germany by I.G. Farbenindustrie in 1926. See also catalytic reforming. 

Sodium perborate oxidation of alcohols by is aided by Aliquat, but also requires the addition of chromium oxide [17]. However, the long reaction times at 60-80°C and the variable yields do not make the procedure particularly attractive. In contrast, direct epoxidation of a,p-unsaturatcd ketones has been conducted with moderate success using sodium perborate catalysed by tetra-n-hexylammonium hydrogen sulphate [18, 19]. 

Figure 9.10 Depth profile for a non-conducting chromium oxide layer on chromium based alloy measured by rf CDMS. (A. I. Saprykin, J. S. Becker et ai, Fresenius /. Anal. Chem., 358, 145 (1997). Reproduced by permission of Springer Science and Business Media.)...

Histological examination of the brain and nervous system did not reveal abnormalities in rats fed 2,040 mg chromium(III)/kg/day as chromium oxide in the diet 5 days/week for 2 years (Ivankovic and Preussmann 1975) however, more sensitive neurological, neurochemical, or neurobehavioral tests were not conducted. 

The dehydrogenation catalyst must be sufhciently active to allow for very short contact times and the use of low temperatures, to minimize thermal cracking reactions. Carbon deposits are eliminated by heatihg in the presence of a gas containing oxygen. -This means that the catalyst must be thermally stable to avoid being deactivated during the oxidation of the deposits. The best catalysts contain alamina and chromium oxide, but these cannot be employed in the presence of steam. Operations are conducted at a temperature between 550 and 700 C, and low pressure, less than 0.1.10 Pa absolute. 

The corrosion resistance of stainless steels and nickel-based alloys in aqueous solutions can often be increased by addition of chromium or aluminum. " Chromium protects the base metal from corrosion by forming an oxide layer at the surface. Chromium is also considered to be an important alloying metal for steels in MCFC applications. Chromium containing stainless steel, however, leads to the induced loss of electrolyte. Previous studies done to characterize the corrosion behavior of chromium in MCFC conditions have shown the formation of several lithium chromium oxides by reaction with the electrolyte. This corrosion process also results in increased ohmic loss because of the formation of scales on the steel. Aluminum additions similarly have a positive effect on corrosion resistance. " However, corrosion scales formed in aluminum containing alloys show low conductivity leading to a significant ohmic polarization loss. 

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