Measurements of the parabolic sulfidation kinetics were carried out at sulfur pressures ranging from i0 -Iz to 10 -2 arm and at temperatures in the range 600~176The effect of sulfur activity on these kinetics is most pronounced at low sulfur pressures. Temperature exhibits the largest influence on these kinetics at high sulfur pressures. An expression is derived for the parabolic rational rate constant in terms of the chemical diffusivity and nonstoichiometry of iron sulfide using the Wagner equation for scaling by iron diffusion and the Libowitz point defect model involving a strong repulsive interaction between iron vacancies to relate nonstoichiometry to sulfur pressure. The predicted values for these rate constants were in good agreement with those found experimentally. A comparison of available results on the parabolic scaling rates at sulfur pressures ranging up to 1 atm suggests that a transition in scale texture with sulfur pressure influences the sulfidation rates since iron diffusion is more rapid in the "c" than in the "a" crystallographic direction of iron sulfide.

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The oxidation kinetics of Fe-Mn alloys containing up to 59 w/o (weight per cent) Mn exposed to carbon dioxide-carbon monoxide atmospheres at 1000~ have been determined by a thermogravimetric technique. The experimental conditions were chosen in order that the reaction would lead to formation of a single-phase manganeseo-wustite [(Fe Mn)O] scale. The rate of parabolic oxidation decreased and the manganese content in wustite increased with increasing manganese content in the alloy. A diffusion model, which is based on equations derived by Wagner for metal diffusion through the scale under chemical activity gradients, ]eads to a description of the scaling kinetics, and to evaluations for the self-diffusion coefficients of iron and manganese and the nonstoichiometry as a function of the manganese content in wustite.

An apparatus is described to measure volumetrically the amount of gas adsorbed by a catalyst a t constant pressure and at exposure times as short as 0.1 min. The volumes of oxygen adsorbed by a technical silver catalyst a t pressures of 200, 400, and 700 mm. and in the temperature range of 180" to 300" C. have been measured. Surface area determinations of 0.33 t o 0.38 sq. meter per gm. of catalyst by physical adsorption and chemisorption methods show that each silver atom of the surface is associated with approximately one osygen adatom a t a monolayer coverage. The initial rate of adsorption of oxygen is directly proportional to its pressure. Observed transitions in the oxygen adsorption rates indicate that more than one type of oxygen comples occurs on the catalyst surface. The Elovich equatioli provides the best approximation of the adsorption rate data but is of limited applicability in interpretation of the ~iiechanism of adsorptio~i. 1:alues of 22-29 Iccal./~ilole and 17-25 lical./mole have been calculated for the apparent activation energy and isosteric heat of adsorption respectively.