Self-Diffusion in α White Phosphorus

Abstract

The coefficient of self-diffusion in α white phosphorus from 0° to the melting point is given by the equation D=1.07×10−3exp[−9400/RT]+2×1046exp[−80 600/RT]cm2sec−1.Only the first term is important for temperatures below 30°, where the vacancy mechanism is believed to operate. The activation energy in this range is in excellent agreement with the value predicted from the latent heat of fusion. A second mechanism begins to become important above 30°, with an activation energy of 80 600 calories and an exceedingly large entropy. This process is interpreted as a comparatively large scale disorder which arises on multiple vacancies. The entropy and energy are consistent with the view that liquid microphase regions containing, on the average, about 130 molecules and 10 distributed vacancies are the principal centers of diffusion near the melting point.