Glass - Back to the Future!

Presenting Author:
Jean-Marc Delaye

article posted 22 March 2016

Jean-Marc Delaye has been graduated from the “Ecole Supérieure d’Electricité”, (Gif/Yvette, France) in 1987. He pursued his studies with a PhD at CEA Saclay dedicated to the study of diffusion mechanisms in amorphous materials using classical molecular dynamics. In 1995, he was engaged at CEA Saclay to work on radiation effects in nuclear glasses using computational methods and migrated to CEA Marcoule in 1997. He became Research Director in the field of nuclear glass modelisation in 2012.

Structural and mechanical property changes under ballistic effects in borosilicate glasses: a classical molecular dynamics study

Dimitrios A. Kilymis1, Le-Hai Kieu2, Simona Ispas1 & Jean-Marc Delaye2*
1 Laboratoire Charles Coulomb (L2C), UMR 5221 CNRS-Univ. Montpellier, Place Eugène Bataillon — CC069, F-34095 Montpellier Cedex 5, France
2 CEA, DEN, DTCD, SECM, F-30207 Bagnols-sur-Cèze, France

In France, nuclear glasses used to confine long lived actinides are aimed to be stored in a deep geological repository. Then it is important to guarantee their radiation resistance, in particular under the nuclear energy deposition which is responsible for the macroscopic property changes: decrease of the hardness, increase of the fracture toughness [1].
To better understand the origin of these modifications, classical molecular dynamics simulations have been performed on simplified nuclear glasses (SiO2–B2O3–Na2O). The ballistic effects have been first investigated on structures prepared with various initial densities. After the accumulation of displacement cascades the irradiated structures converge towards each other with a partial removal of the initial shifts [2]. Then crack propagation has been modelled by applying an external tensile stress on a pristine and a disordered structure prepared with a high quench rate to reproduce the radiation effects (Figure 1). The increase of the plasticity associated with the glass depolymerization was shown to be responsible for the increase of the fracture toughness [3]. Concerning the hardness, its decrease after irradiation has been correctly reproduced by the molecular dynamics simulations and correlated to the structural modifications at the atomic scale [4]. In the simplified nuclear glass, the decrease of the hardness can be explained predominantly by the depolymerization of the network rather than the increase of the free volume.

[1] S. Peuget, J.-M. Delaye, C. Jegou, Journal of Nuclear Materials, 444 (2014) 76.
[2] D.A. Kilymis, J.-M. Delaye, S. Ispas, Journal of Non-Crystalline Solids, 432 (2016) 354.
[3] L.-H. Kieu, J.-M. Delaye, C. Stolz, Journal of Non-Crystalline Solids, 358 (2012) 3268.
[4] D.A. Kilymis, J.-M. Delaye, Journal of Non-Crystalline Solids, 401 (2014) 147.
Figure 1: Crack propagation in a simplified nuclear glass (SiO2-B2O3-Na2O) at four different times. Top left: 26ps, top right: 32ps, bottom left: 40ps, bottom right: 44ps.