Kinetics of Melting and Crystallization of Phosphorus Pentoxide

Abstract

The melting and crystallization of tetragonal phosphorus pentoxide has been investigated by the use of a microscopic technique. Superheating of about 50° above the melting temperature was possible. Melting was heterogeneous and began only at free surfaces or grain boundaries but never within a crystal. At a supercool or superheat of 10°, the respective rates were approximately 5 and 10 A/sec. The dependency of melting and crystallization on temperature, time, crystal direction, morphology, and preparation history was studied. Under ideal conditions, the observed rates were in almost quantitative agreement with those calculated from a simple model based primarily on viscosity considerations.