The phases of HMX and their transitions were investigated by thermal analysis using X‐ray diffraction. Series of diffraction pattern were measured, while the samples were heated and cooled. The thermal expansion coefficients and the colume changes at the transitions were extracted from the diffraction series. A contraction of β‐HMX was found before changing into δ‐HMX resulting in a high volume difference during the transition. On cooling, the reconversion of the high temperature phase requires days. It is further slowed down by decomposition products, which are formed at temperatures beyond 490 K. The final reconversion results in mixtures of α‐and βHMX. The mechanical sensitivities and the buring rates of the HMX phase were determined. The high sensitivity of δ‐HMX against impact together with its slow reconversion creates handling risks when the HMX is exposed to temperatures above 440 K.

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Advanced evaluation techniques as Rietveld refinement applied to series of temperature resolved X‐ray diffraction measurements, provide an improved insight into the lattice dynamics. The transition paths of ammonium nitrate are clearly defined and coexisting phases are quantitatively determined. The curves for the elementary cell parameters of the different phases as a function of temperature exhibit hitherto unknown details and elucidate expansion and transition mechanisms. They are used for the calculation of the volume changes during the transitions and the volumetric and linear expansion coefficients.

A method is described to study the structural behavior of solids subjected to various temperature programs. The instrumentation consists of a high-or lowtemperature device, a temperature programmer, a system for energy-dispersive X-ray diffraction and a data processing and storing unit and allows the fully automatic acquisition of series of spectra. A strong data reduction is performed by summing up difference diagrams. Plotting the resulting values versus temperature yields curves comparable to those obtained by differential scanning calorimetry (DSC) or thermal gravimetry (TG). A kinetic evaluation as used in the case of DSC or TG curves is possible. The method was applied to study the thermal behavior of a mixture of ammonium nitrate with zinc oxide. The curves indicate the strong anisotropic thermal expansion of the ammonium nitrate phase IV below 323 K, its transition to phase II at 325-329 K and the solid-state reaction with zinc oxide within the temperature interval of 353-383 K.

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