Assessment of glass-forming ability and the effect of La_2O_3 on crystallization mechanism of barium-lead-zinc phosphate glasses

摘要

Differential scanning calorimetry (DSC) was used in this work to study the effect of La_2O_3 addition on crystallization mechanism of barium-lead-zinc phosphate glasses. Bulk glasses from two different routes (using P_2O_5 and H_3PO_4 as starting materials) presented only one crystallization peak. An assessment of glass-forming ability (GFA) was performed from recent theory that is connected to glass stability (GS), and is also correlated to critical cooling rate, q_(cr). Systems with high La_2O_3 content presented some of the highest GS values and estimated critical cooling rates (q_(cr)) lower than 0.079 K/s. For both routes were determined the activation enthalpies for crystallization, that were 126±12 kJ/mol (for P_2O_5) and 110±32 kJ/mol (for H_3PO_4). The calculated Avrami n parameters, based on exothermic crystallization peaks, were 3.50±0.33 (for P_2O_5) and 3.09±0.91 (for H_3PO_4), considering data from the lowest heating rate (5 K/min). These values suggest that the DSC peaks should be associated to volume crystallization, due to La_2O_3 influence, and crystallization did not change significantly using different routes.