Thermochimica Acta, Vol.254, 235-247, 1995
Thermal-Decomposition Studies .19. Kinetics and Mechanism of Thermal-Decomposition of Copper Ammonium Chromate Precursor to Copper Chromite Catalyst and Correlation of Surface Parameters of the Catalyst with Propellant Burning Rate
The thermal decomposition of copper ammonium chromate (CAC), which is a precursor of copper chromite (CC) catalyst (used as a ballistic modifier in solid propellants), has been thoroughly studied. The DTG curves show that there are three main peaks at about 286, 440 and 740 degrees C, whereas DTA gives peaks at 254 (endo), 278 (exo), 408 (exo) and 699 degrees C (endo). The kinetic parameters for the prominent and clear-cut first stage in TG (DTG peak at 286 degrees C) are E=236 kJ mol(-1), A = 1.51 x 10(21) s(-1), and Delta S = 136 J K-1 mol(-1). The mechanism of this decomposition reaction is identified as a phase boundary reaction with spherical symmetry, as per the equation g(alpha) = 1 - (1 - alpha)(1/3). The surface parameters of the CC samples obtained by calcination of CAC, at different temperature regimes compatible with TG data, have been determined. The surface area of the CC decreases when the calcination temperature increases. The surface area also decreases when CC samples are washed with acetic acid. X-ray diffraction (XRD) patterns of CC samples obtained from higher temperature calcinations of CAC differ from those obtained at lower temperatures. The propellant burning rate is enhanced by the addition of CC and increases when the Lewis acid amounts of the catalyst sample increase. These correlations have been established for the first time for CC catalysts used in propellant technology.