Thermal characterization of ammonium alum

Thermal decomposition of ammonium alum was studied by simultaneous thermogravimetry (TG)-differential scanning calorimetry (DSC) attached to a Fourier transform infrared (FTIR) spectrometer, so that each mass loss was related with the simultaneous endo- or exothermal behavior and to the FTIR absorption produced by the evolved gases. Apart from some clear dehydration and desulfation processes, other overlapping peaks were observed by DSC, TG, and FTIR. Optimal fitting to logistic mixture models was performed to separate the overlapping processes. Deconvolution of overlapping DTG peaks resulted in single constituent peaks, which were related to plots of some specific FTIR bands along time. Thus, a more accurate insight of the chemical processes taking place was obtained.