Differential scanning calorimetry and thermal desorption analysis of crystalline synthetic quartz

High-purity crystalline synthetic quartz samples with different Al contents have been analysed by using differential scanning calorimetry (DSC) and thermal desorption analysis (TDA). The DSC measurements revealed an exothermic process in the 623–673 K temperature range with an enthalpy value of the order of 0.3 J/g following thermal dissociation of aluminum-related centers and hydrogen emission as detected by TDA: by considering the high enthalpy variation, the exothermic effect is tentatively attributed to a lattice relaxation process occurring near the Al–OH or Al–M dissociated centers.