Investigation on the thermal expansion of α-CL-20 with different water contents

The thermal expansions of three kinds of alpha-CL-20 crystals have been investigated in the temperature range from 30 to 130 A degrees C by means of various-temperature X-ray powder diffraction (XRD) together with Rietveld refinement. The crystals were characterized by SEM, XRD, FTIR, and DSC/TG. The results show that the three samples contain 1/2, 1/4 mol, and none structural water, respectively. The alpha-CL-20 crystals all perform linear and anisotropic thermal expansion, while some differences exist. The unit-cell axes increase linearly with increasing temperature except for the a-axis. The expansion along the a-axis switches from positive to negative thermal expansion at 90 A degrees C for alpha-CL-20 center dot 1/2H(2)O. The a-axis exhibits positive thermal expansion (PTE) with thermal irresilience for alpha-CL-20 center dot 1/4H(2)O while PTE with thermal resilience for the anhydrous alpha-CL-20. The differences are caused by the structural water. The removal of structural water leads to the collapse of a-axis, further results in structural changes of the unit cell. Different water contents can cause different degree of structural changes, leading to the difference of thermal expansion behaviors.