Ferric and Chromic Oxides

Yates, D. E., and T. W. Healy (1975), "Mechanism of Anion Adsorption at the Ferric and Chromic Oxide/ Water Interfaces", J. Colloid Interface Sci. 52, 222-228. 

Yates, D.E. Healy,T.W. (1975) Mechanism of anion adsorption at the ferric and chromic oxide/water interfaces. J. Colloid Interface Sd. 52 222-228... 

Mixed gels of hydrous ferric and chromic oxides were prepared by the addition of an equivalent amount of ammonium hydroxide to mixtures of the solutions of ferric nitrate (0.5M with respect to Fe20j) and chromic nitrate (0.5M with respect to Cr203). The dual gels were washed free of nitrate ions and air- or oven-dried. A series of mixtures corresponding to 20, 40, 60, and 80% Fe203 was prepared. 

H. Forestier and G. Chaudron found that ferric and chromic oxides form solid soln. 

The mechanism by which chromate passivates steel has been studied extensively, and it appears hkely that protection is afforded by a combination of adsorption and oxide formation on the steel surface. Adsorption helps to polarize the anode to sufficient potentials to form very thin hydrated ferric oxides that protect the steel. Because the oxide film is invisible on steel, articles protected by chromate remain bright in otherwise aggressive environments. The oxide film is a mixture of ferric and chromic oxides and is kept in good repair by adsorption and oxidation, with very little loss of metal as long as sufficient chromate remains in solution. 

The protectiveness of the film appears to be related to its composition. At temperatures up to 175°C the scale, as determined by x-ray diffraction, is composed of mixed hydrated ferric and chromic oxides. At higher temperatures the amount of hydrated oxide decreases, and the amount of anhydrous alpha ferric oxide containing chromic oxide in solid solution increases. At 250°C and higher, only the anhydrous oxide is found in the protective scale. 

For the ferric oxide/aluminum (Fe 2O 3 /Al), manganese dioxide/ aluminum (MnO 2 /Al), and chromic oxide/magnesium (Cr 2O 3, /Mg) systems, slight gas phase involvement is indicated by the 3-4 fold rate increase observed as the external pressure is raised from 1 to 150 atm. The chromic oxide /aluminum system, however, reportedly burns at exactly the same rate - 2.4 millimeters /sec - at 1 and 100 atm suggesting that it is a true "gasless" system [1]. 

The technique of differential thermal analysis (D.T.A.) has been extensively employed in the study of clay and other minerals for elucidating their structures for more than three decades. The application of D.T.A. as a tool has not been widely made to the systematic study of solid catalysts. Only a few references on the subject could be foimd 1-6). In the present article, differential thermal studies of a number of solid catalysts like chromic oxide gels, ferric oxide gels, and chromic oxide-ferric oxide are reported. An attempt has also been made to correlate the data with x-ray... 

An analogous third series of gels was prepared in which the ferric oxide gel and chromic oxide gel were separately precipitated and mixed in moist condition. 

In small-scale syntheses, a wide variety of oxidants have been employed in the preparation of quinones from phenols. Of these reagents, chromic acid, ferric ion, and silver oxide show outstanding usefulness in the oxidation of hydroquinones. Thallium (ITT) triduoroacetate converts 4-halo- or 4-/ f2 -butylphenols to l,4-ben2oquinones in high yield (110). For example, 2-bromo-3-methyl-5-/-butyl-l,4-ben2oquinone [25441-20-3] (107) has been made by this route. 

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