Manganese surface condition

The corrosion rate depends upon the steel composition surface condition and the angle of exposure. Increase in carbon, manganese and silicon content of the steel results in decrease in corrosion rate although if manganese is present as sulfide as in free-machining steels, corrosion resistance decreases. The presence of copper increases the corrosion resistance. 

This study focused on the deactivation of the Mn/Ce catalysts during reaction. The catalytic oxidation of phenol in aqueous solution to carbon dioxide, water and other side-products was selected as the test reaction. Catalysts were prepared from amorphous precursors using the citrate method and controlling the calcination temperature. Activity performance as a function of the time on stream was studied by simultaneously analyzing the conversion of phenol, the total organic carbon content of the catiyst, the cations eluted and the elemental composition of both cerium and manganese. Experimental conditions were widely varied. Fresh and used catalysts were also analyzed by BET surface area, X-Ray Diffraction and X-Ray Photoelectron Spectroscopy. 

Highly Catalyzed Experiments. In conjunction with experiments in which the manganese concentration was 2000 ppm, the model was first used to determine the mass transfer coefficient of calcium sulfite (T=40°C, pH=5.0). A reaction order of 1.5 was obtained from previous liquid phase kinetic studies with a rate constant of 85 1 ° 5 mol 0,5 sec-1 (25). Computer curves were generated using a series of mass transfer coefficients and plotted along with the experimental kinetic results on Figure 7. A mass transfer coefficient of 0.015 cm/sec most closely fits the data. The bulk pH drops quickly during the initial several seconds and then stays around 2.9, but the surface pH remains almost constant at 5.15 which implies that the oxidation only has small influence on the surface conditions. 

Figure 1. Percentage of thiol conversion vs surface oxygen/manganese content of various manganese nodules. Condition Thiol = 2.5 x lO mol., Nodule = O.lg, Temp. = 35°C.

The most direct evidence for surface precursor complex formation prior to electron transfer comes from a study of photoreduc-tive dissolution of iron oxide particles by citrate (37). Citrate adsorbs to iron oxide surface sites under dark conditions, but reduces surface sites at an appreciable rate only under illumination. Thus, citrate surface coverage can be measured in the dark, then correlated with rates of reductive dissolution under illumination. Results show that initial dissolution rates are directly related to the amount of surface bound citrate (37). Adsorption of calcium and phosphate has been found to inhibit reductive dissolution of manganese oxide by hydroquinone (33). The most likely explanation is that adsorbed calcium or phosphate molecules block inner-sphere complex formation between metal oxide surface sites and hydroquinone. 

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