Interfacial structures of spinel crystals with borosilicate nuclear waste glasses from molecular dynamics simulations

Abstract

Spinel crystal formation presents a critical issue and glass formulation in nuclear waste glass processing. In this paper, the interfacial structures of the model borosilicate nuclear waste glasses, the international simple glass (ISG), with two types of spinel crystals, namely the MgAl 2 O 4 and NiFe 2 O 4 , were studied using classical molecular dynamics simulations with effective partial charge potentials and recently developed composition-dependent boron-related parameters. The simulation results revealed the structural features of the borosilicate nuclear waste glasses and their interfaces with the two types of spinel crystals. It was found that there exist notable structural changes of glasses close to the interfacial region, affected by the adjacent crystal structures, terms of preferential segregation and ordering of cations, as well as ctaion coordination numbers. Specifically, the fraction of fourfold coordinated boron (B 3 ) in glass near the interface decreases as compared to the bulk glass. In addition, the amount of fourfold coordinated Al decreases while fivefold Al increases in the glass region close to the glass-crystal interface, which suggests indication of initial stage of crystal growth as Al adopts higher (sixfold) coordination like in the crystal as compared to majority of fourfold coordination in the glass. These interfacial structure changes obtained from MD simulations provide evidence of the influence of the precipitated crystals on the surrounding melt and glass and the initial stage of crystal growth. 4584 | SUN aNd dU How to cite this article: Sun W, Du J. Interfacial structures of spinel crystals with borosilicate nuclear waste glasses from molecular dynamics simulations. J Am Ceram Soc. 2019;102:4583-4601. https://doi.

Effects of Surface Orientation and Termination Plane on Glass‐to‐Crystal Transformation of Lithium Disilicate by Molecular Dynamics Simulations

“…As the crystal part is fixed in this study, the interface area consists of the terminated layer from crystal side and few angstroms of surface region within the glass region, which is generated and considered as glass bulk due to the periodic boundary condition. [27,28] As expected, the crystal surface terminations impact atomic reorganization in glass that comes directly in their contact. In Figure 5b, the two terminations of LS2(110) result in different z-density profiles for the two interface regions.…”

“…For example, the different coordination numbers of Al atoms in MgAl 2 O 4 glass and spinel crystal (four in glass and six in crystal) allow the ability of identifying crystal growth by analyzing Al coordination changes in different regions in glass part. [ 28 ] In the lithium silicate system, the Si atoms in both LS2‐crystal and LS2‐glass demonstrate very similar behaviors on PDF, BAD, and coordination number distributions. The most noticeable difference in short range comes from pairs including Li atoms.…”

“…In the early studies mentioned earlier, this distinction was based on the atomic density profiles along the interface normal. Recently, Sun and Du [27,28] reported the structures of interfacial region between aluminoborosilicate glass and MgAl 2 O 4 spinel crystals using the recently developed classic interatomic potentials. [29] The results show that the coordination number changes, and the bond distance between O and Al/B atoms can be a useful indicator of crystallization of glass owing to the distinct Dr. W. Sun, Prof. V. Dierolf, Prof. H. Jain Institute for Functional Materials and Devices Lehigh University Bethlehem, PA 18015, USA E-mail: h.jain@lehigh.edu…”

Effect of iron redox ratio on the structures of boroaluminosilicate glasses

“…32,31 Understanding how iron oxide affects the structure and properties of borosilicate melt and glass is particularly important in the immobilization of nuclear waste through vitrification. 33 The process is also known as vitrification, a well-accepted way for nuclear waste disposal, 34 due to the high chemical durability of the borosilicate glasses and their relatively low melting temperature of glass processing. 35,36 Iron is one of the most common transition elements found in borosilicate nuclear waste glasses.…”

“…31 Classical MD has been proved to be an efficient way to provide systematic studies on short-and medium-range structures in multi-oxide glasses. 33,[50][51][52][53] The existence of two oxidation states of iron and composition dependence of coordination change of boron makes simulations of iron oxide-containing borosilicate glass a great challenge. Recently, Deng and Du 54 have reported a set of partial charge pairwise potential for borosilicate glasses that is compatible for a large number of cations.…”