Non-isothermal kinetics of decomposition of AlNH4(SO4)(2).12H(2)O by EGA-MS

Real-time multiple-ion detection trend analysis mass spectrometry has been employed to study the temperature-programmed decomposition of AlNH4(SO4)(2). 12H(2)O in the temperature range 300-1200 K. Significant correlations are established with certain non-isothermal solid state kinetic rate expressions through the use of fraction release plots obtained from Evolved Gas Analysis Mass Spectra (EGA-MS). The EGA mass spectra clearly resolve the dehydration stage and various other stages associated with the thermal decomposition. The dehydration step is concomitant with stage I of a three-stage ammonia release followed by the final decomposition of Al-2(SO4)(3). These stages are found to comply with models based on random nucleation and diffusion approaches. A change in rate-governing mechanism was noticed with increase in the heating rate for the dehydration step. Relevant Arrhenius parameters such as the activation energy and preexponential factor were determined for all the decomposition stages. The ultimate product resulting from the decomposition was confirmed as gamma-alumina by X-ray diffraction studies.