Submicron-Sized Gamma-HMX: II. Effect of Pressing on Phase Transition.

In a previous article we described the preparation and initial characterization of a novel submicron-sized HMX (sm-HMX). Using Raman spectroscopy, the sm-HMX was found to be the gamma polymorph and to be stable with respect to conversion to beta-HMX under ambient conditions for at least a year. Pressing of sm-HMX powder in a small diameter pellet press at pressures from 10,000 to 31,000 psi and 1- to 5-min hold times was found to promote the gamma-to-beta polymorphic phase transition. The fraction converted and rate of conversion versus time after pellet removal from the press were found to fit a sigmoidal curve, indicating nucleation and growth as a possible polymorphic transition mechanism. [ABSTRACT FROM AUTHOR]