Glass - Back to the Future!

Presenting Author:
Susanne Krüger

article posted 7 April 2016

Susanne Krüger was born in 1985, in 2005–2011 studied for a Bachelor's degree and subsequent Master's in Materials Science and Engineering with specialization in glass and ceramic materials at Clausthal University of Technology. Currently working as a doctoral candidate studying crystallization in glasses at the Institute of Non-Metallic Materials in Clausthal.

Towards single crystallization events of glass-forming liquids in DSC experiments

S. Krüger* & J. Deubener
Institute of Non-Metallic Materials, Clausthal University of Technology, Germany

Recently it has been shown that levitated lithium disilicate droplets fully crystallize from the surface due to growing of one or two crystals [1]. Another study reports on individually shaped DSC exotherms for each run if supercooling of a single lithium disilicate sample in a platinum crucible was repeated [2]. Both results indicate that the liquid does not crystallize by a large ensemble of crystals but is initiated by nucleation of just one or few crystals. In order to understand the involved heterogeneous nucleation and crystal growth processes, isothermal treatments are performed in the present study. Therefore, a single lithium disilicate sample is repeatedly heated above the melting point Tm, quenched to a constant temperature below Tm and hold for up to 60 min. As expected crystallization exotherms show a different shape in each run. Using an instantaneous Avrami analysis the number of nuclei formed during the crystallization process is determined due to the sudden change of the Avrami coefficient in dependence of the crystallized fraction. To confirm the calculated crystal number densities samples showing different crystallization peaks are studied by optical microscopy. From the analysis the growth direction of the crystals and thereby the origin of nucleation (wall of the platinum crucible, melt-air interface or secondary phases) are determined.

[1] K.S. Ranasinghe, C.S. Ray, D.E. Day, J.R. Rogers, R.W. Hyers, T. Rathz, J. Mater. Sci. 42 (2007) 4291–4297.
[2] S. Krüger, J. Deubener, J. Non-Cryst. Solids 388 (2014) 6–9.