Borosilicate and Boroaluminosilicate Glasses

Borosilicate and boroaluminosilicate glasses are important glass compositions with wide industry and technology applications. These glass compositions are also the archetypes of multicomponent boron-containing oxide glasses. However, due to their complicated structural nature and particularly boron coordination change with composition and thermal history, atomistic simulations of these glasses lag behind the more extensively studied silicate glasses. Classical and ab initio molecular dynamics simulations, on the other hand, can provide valuable information at the atomic scale thus help understand the experimental observed properties and behaviors (for example the well-known boron anomaly). In this chapter, we start with the introduction of the structure features of these glasses from experimental studies and theories based on them. Particularly, experimental determination and theoretical models that describe the fraction of four-coordinated boron ( N 4 ), one of the most important structural features in these systems, as a function of composition (e.g. the R and K values) are introduced. Classical molecular dynamics and ab initio molecular dynamics simulation methods, both of which have been used to simulate borosilicate and related glasses, are briefly discussed in terms of their advantages and limitations. This is followed by discussions of two important aspects of classical molecular dynamics simulations: the development and evaluation of the boron-related empirical potentials, and the effects of simulation details (i.e. cooling rate and system size). Applications of these new empirical potentials in simulating bulk/surface structures of borosilicate and other multicomponent boron-containing glasses including bioactive and nuclear waste glasses are presented as examples of applications of molecular dynamics (MD) simulations. A summary of B 2 O 3 and related empirical potentials with their functional forms and parameters, including a few that have been recently developed, are presented as supplemental materials of the chapter.