Mechanism and Kinetics of Ammonium Paratungstate Decomposition Under Different Gas Atmospheres and Heating Conditions Ammonium paratungstate (APT) takes an important part in tungsten (W) production. Tungsten trioxide or tungsten blue oxide is formed depending on the thermal decomposition conditions of APT. Tungsten blue oxide includes either stoichiometric and nonstoichiometric tungsten oxides or tungsten bronzes. In industry, W is used as filaments in illumination bulbs, cathodes in high power bulbs and rocket nozzles in space vehicles. Hexagonal structured tungsten oxide and tungsten oxide bronzes find area of utilization as gas and humidity sensors in electronic devices because of their open tunnel structures.
Various findings are proposed about thermal decomposition steps and products of APT in literature. Amount of sample, heating rate, gas atmosphere and type of crucibles play important role in obtaining different findings. Although there are numerous studies on the decomposition mechanism of APT, no investigation was found about kinetics of these thermal decomposition steps.
In this study, Thermogravimetric, Differential Thermal and Mass Spectrometric Analyses (TGA/DTA-MS) were carried out under nonisothermal and isothermal conditions in dry air and argon atmospheres to determine the thermal decomposition mechanism of APT. The characterizations of the intermediate and final thermal decomposition products were made by using X-ray Powder Diffraction (XRD) and Fourier Transform – Infrared Spectroscopy (FT-IR) analysis techniques. Apparent activation energies, preexponential factors in kinetic equations belonging to thermal decomposition steps and kinetic model equations were determined. Additionally, the characterizations of the thermal decomposition products of APT obtained at different temperatures under its own atmosphere in an evacuated system were carried out by using XRD and FT-IR analysis techniques.
