Vapor Pressure of Silicon and the Dissociation Pressure of Silicon Carbide

Abstract

The vapor pressure of silicon and the dissociation pressure of silicon carbide have been obtained from total weight loss experiments with Knudsen effusion cells. Combination of the measured data with known entropies yields at 298°K for the heat of sublimation of silicon to silicon atoms 108.4±3 kcal and for the heat of the reaction SiC_(s)=Si_(g)+C_(s) 126.0±3 kcal. From the pressure studies and from phase equilibria for the condensed phase silicon‐carbon system, the heats of formation for both the cubic and hexagonal modifications of silicon carbide are concluded to be −15.0±2 kcal.