It is well known that the variation i the crystallised fraction, x(t), can be determined directly by optical microscopy (OM) or indirectly by differential scanning calorimetry (DSC) under isothermal conditions. In this work, the kinetic crystallisation parameters E (activation energy) and n (Avrami index) of a quasi-stoichiometric lithium disilicate glasss (Li2O.2SiO2-Ls2) were studied. First, bulk samples were heat treated in a vertical tube furnace between 500-530 deg C for different periods of time, and were carefully prepared. Furthermore, the same samples were then heated in a calorimeter from room temperature to 850 deg C at 10C/min. The following E and n values were obtained: (i) OM: 462:2 +/- 1.23 kJ/mol and 4; and (ii) DSC: 187.5 +/- 0.45 kJ/mol and 2.4. The results indicated that the activation energy was reduced due to the formation of new crystals and growing of the pre-existing crystals during the DSC experiments, and that the predominant crystallisation mechanism in the samples changed according to the chosen thermal history.
