Difference thermal analysis of crystalline solids by the use of energy-dispersive X-ray diffraction

A method is described to study the structural behavior of solids subjected to various temperature programs. The instrumentation consists of a high- or low-temperature 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.