Overheating-Dependent Heterogeneous Crystal Nucleation in a Lithium Disilicate Melt

The influence of thermal history on the kinetics of liquid-solid transformations is investigated for heterogeneous crystal nucleation near the liquidus temperature in a melt with lithium disilicate composition in contact with a PtRh10 carrier. It is shown that the achieved undercooling depends on the preceding superheating protocol. This is explained by a distribution of nano-sized cavities on the surface of the precious metal, in which crystalline clusters can persist above the liquidus temperature for a characteristic time. In series of different surface quality of the PtRh10 carrier and for air purging, these times are in the range of 5-20 s, which seems relatively long compared to metallic melts, where this phenomenon was first observed in the millisecond range. The high viscosity of the silicate melt at the liquidus temperature is discussed as the reason for the difference in the persistence time.