Kinetic study of the solid phase reaction of ammonium nitrate and copper oxide by the use of fast X-ray diffraction

The solid state reaction of ammonium nitrate and copper oxide was studied by the use of energy dispersive and angle dispersive x-ray diffraction. The reaction takes place with-in the temperature interval 110 to 150 ~ and consists of two steps. The product of these consecutive reactions is the diammine copper complex. The relative concentrations of the species involved were evaluated by summing up difference x-ray spectra. The resulting curves were analyzed by a computer program to obtain the kinetic constants of the reactions. The doping of ammonium nitrate with small amounts of diammine metal complexes influences significantly its phase transitions [1]. The complexes can be prepared by a solid state reaction of the metal oxide with ammonium nitrate [2,3], which requires the knowledge of the reaction kinetics. In addition to the methods of thermal ana-lysis, x-ray diffraction provides a convenient way to study solid state reactions [3]. Thermal analysis by x-ray diffraction uses a heatable sample cell and fast detectors for a fast recording of the diffraction pattern. We used the energy dispersive x-ray diffraction (EDXRD) with a Si(Li) solid state detector (see Giessen and Gordon [4] and Buras et al. [5]) and angle dispersive diffraction with a position sensitive proportional counter (PSPC) [6]. These methods allow a relatively fast acquisition of x-ray spectra during heating experiments with heating rates comparable to that of DTA and TG. In this paper we investigated the reaction of ammonium nitrate and copper oxide in closer detail. Main interest was focussed on the kinetics of the reaction in order to get reliable data for the phase stabilisation process