Thermic investigations of hexagonal hydrogen bronze,HxWO3

The thermic-kinetic behaviour of hydrogen tungsten bronze, H_xWO₃, was investigated by differential scanning calorimetry and X-ray analysis. It is shown that the thermal decomposition of bronze into hydrogen and WO₃, is exothermic. Further, it is shown that the hexagonal WO₃ system is exothermally transformed (irreversibly) to the monoclinic WO₃ system. Activation energies, frequency factors and rate constants of the corresponding processes are determined. It is shown that the hexagonal WO₃ system adsorbs hydrogen at approximately 480 K, and desorbs at room temperature in air or an argon-nitrogen atmosphere. It is also shown that H_xWO₃ is unstable and that it decomposes with time, forming brown WO₃ which gives no yellow modification during the WO₃ phase transformation. The newly formed modification adsorbs hydrogen without changing colour.