hydration process (Fruhwirth et al., 1985). The TGA results show that the commercial magnesia had an initial hydroxide content of 5%. Additionally, the hydroxide can also inherit from atmospheric water, which absorbs and hydrates on the hygroscopic MgO surface (Smithson and Bakhshi, 1969). The material was handled under normal environmental conditions, in which H2O uptake was unavoidable. However, the results are in good accordance with comparable data from Aphane (2007), which indicates good validity of the applied method.