Molecular dynamics simulations of the ballistic effects arising from displacement cascades in glasses have been investigated in silica and in a SiO(2)-B(2)O(3)-Na(2)O glass. In both glasses the T-O-T' angle (where T and T' are network formers) diminishes, despite radiation causes opposite effects: while the ternary glass swells and silica becomes denser. We show that radiation-induced modifications of macroscopic glass properties result from structural change at medium/range, reflecting an increasing disorder and internal energy of the system. A local thermal quenching model is proposed to account for the effects of ballistic collisions. The core of a displacement cascade is heated by the passage of the projectile, then rapidly quenched, leading to a process that mimics a local thermal quenching. The observed changes in both the mechanical and structural properties of glasses eventually reach saturation at 2 10(18) alpha/g as the accumulated energy increases. The passage of a single projectile is sufficient to reach the maximum degree of damage, confirming the hypothesis postulated in the swelling model proposed by J.A.C. Marples. (C) 2011 Elsevier B.V. All rights reserved.
Delaye, J. -M. Peuget, S. Bureau, G. Calas, G. 11th International Conference on the Structure of Non-Crystalline Materials (NCM 11) JUN 28-JUL 02, 2010 Paris, FRANCE SI