Possible influence of pores and other structural defects on the temperature of the polymorphic transformation of HMX

Results of experimental investigations of the polymorphic transformation $\beta\to\delta$ of various fractions of HMX are reported; the studies are performed by methods of differential thermal and thermogravimetric analysis, as well as by picnometer tests. With an increase in the crystal size, it is found that the temperature of the beginning of the polymorphic transformation of HMX decreases, and the HMX density also decreases. It is hypothesized that the change in the polymorphic transformation temperature is associated with the dependence of the enthalpy jump on the polymorphic transformation on structural defects.