Comparative effects of thermal quenching and ballistic collisions in SiO2–B2O3–Na2O glass.

Abstract: The differences between the effects of irradiation and thermal quenching were studied in SiO2–B2O3–Na2O glass by molecular dynamics. Classical molecular dynamics simulations reproduced quenching rates between 2×1012 K/s and instantaneous quenching. Each configuration was then subjected to a series of displacement cascades. An acceleration of the quenching rate and the accumulation of ballistic collisions result in qualitatively similar effects: swelling, increasing disorder, depolymerization of the glassy network, a decrease in the mean coordination number of B atoms. Nevertheless, ballistic processes induce specific effects that are not reproduced by accelerated quenching: an even larger degree of disorder, higher potential energy, greater depolymerization around B sites and different free volume distribution. The memory of the initial quenching rate is largely lost following an accumulation of displacement cascades, and the structure of the irradiated glasses adopts a final configuration weakly dependant on the initial state. This study shows that comparing the structure of the initial glass prepared at different quenching rates with the structure of irradiated glasses makes it possible to discriminate between thermal quenching and ballistic effects. [Copyright &y& Elsevier]