Cambridge 7th to 9th September
Presenting Author:
Wenlin Chen
<wec2@aber.ac.uk>
article posted 27 Apr 2015
Wenlin Chen
Wenlin Chen is a PhD student at the Department of Physics at Aberystwyth University in Wales (United Kingdom). His subject is about molecular dynamics simulation of zeolitic glass such as nepheline and ZIF. His other interests include the ab initio modelling of zeolite and performing simulation with GPU computation.
Ion distribution in nepheline glass: A molecular dynamics study
Wenlin Chen*1, Zhongfu Zhou1, Charles Le Losq2,3, Daniel R. Neuville2, George N. Greaves5,6
Understanding the links between chemistry, nanostructure and properties of silicate glasses and melts remains a fundamental problem for Earth and Material Sciences. Central to this, is whether the distribution of mobile metallic ions, like alkalis, can be considered random or not. This drastically affects our understanding of their properties, and ways to model them.
We have performed molecular dynamics
simulations of the alumina-silicate nepheline (KXNa4-XAl4Si4O16) glasses to support the contention that micro-segregation of metallic ions into percolation channels is a universal phenomenon, strongly influenced by their ionic radius and field strength. Five different compositions of alkali ions (X=0,1,2,3,4) were studied with the same process of melting and annealing. Radial distribution functions, VDOS and molecular structure snapshots have been calculated and reveal how K+ and Na+ are indeed distributed non-randomly, creating distinct nanostructure in glassy nepheline and its molten versions.
In particular the confirmation of this nanostructure at the glass transition, at 1200 K, is virtually the same as it is for the glass at room temperature. Moreover, the percolation threshold is crossed in nepheline as K+, with its higher field strength, replaces Na+. In particular this occurs at the same composition at which the melt viscosity is observed to dramatically increase, as well as the boson peak intensity of the quenched glass.
Institutions:
1 Department of Physics, Aberystwyth University, Aberystwyth, Ceredigion, SY23 3BZ, UK
2 Géochimie & Cosmochimie, CNRS-IPGP, Paris Sorbonne Cité, Paris, France.
3 Geophysical Laboratory, Carnegie Institution for Science, Washington D.C., USA.
5 University of Cambridge, Department of Materials Science & Metallurgy, Cambridge CB3 0FS, UK.
6 State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology, Wuhan 430070, China.