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September 1958Oxidation Behavior and the angle 8. Consequently, there is a lack of coordination around the periphery of the drop on recrystallized alumina, making the effect much less spectacular.The magnitude of the contact angle characteristic of recrystallized alumina represents an average of the many local values of 0. The mean value of 60 degrees compared with 78 degrees on a flat sapphire surface dictates a decrease in the extent to which spreading can occur before a contraction on recrystallized alumina. Such spreading and contracting must then be of a magnitude that is too small to give rise to gross fluctuations in 9.of Silicon Carbide 347In conclusion, it may be pointed out that, in general, when a liquid is observed to spread on a solid surface at a constant temperature, such spreading may be due not only to a decrease in yl,, and/or yrr but also may be due, in part, to an alteration in the geometry of the surface associated with dissolution or chemical reactions.The oxidation of purified green silicon carbide in controlled atmospheres was studied by weightgain measurement and by observation of the surface reaction products, including optical measurement of the thickness of the oxide surface film. The rate of oxidation was much greater for silicon carbide in contact with fluid silicate glasses than for silicon carbide alone. In a vacuum of 0.1 mm., oxidation proceeded with loss of weight, because of the formation of volatile SiO, and at a greater rate than at atmospheric pressure. It is postulated that the rate-controlling process in the normal oxidation of silicon carbide is the formation of solid Si02 on the surface.

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Knowledge of the compounds of hydrated calcium silicate and their equilibria is important in cement technology and in regard to the use of siliceous minerals in cement.Hydrated calcium silicate is gelatinous at room temperature, regardless of method of preparation or time. However, the units of physical structure may be well-organized and definite, since X-ray analysis has shown that most inorganic gelatinous or amorphous materials are in reality crystalline, while all are crystalline (to X-rays) whose atoms or radicals are dior monovalent.1 A diffraction pattern has in fact been reported by Chassevant2 for Paul S. Roller and Guy Ervin, Jr.Vol. 62 coagula.7,8 A third method of experiment consists in precipitating hydrous calcium silicate and treating this with lime water. Because in this method the initial solid phase is a hydrous compound more or less closely related to the final products of equilibrium, a comparatively rapid approach to equilibrium would be expected. This in fact has been realized in the present work.Chemical analysis has in the past frequently neglected the correction due to dissolved silica.The association constant, solubility product constants, and one of the ionization constants, were calculated to a known precision. A high tendency toward association is evidenced.College Park, Md.

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