Abstract
Lithium disilicate melt in DSC containers made of platinum rhodium alloy PtRh20 is repetitively supercooled at two different oxygen partial pressures. Using 5 different cooling rates and 332 runs per cooling rate, kinetic data of heterogeneous crystal nucleation are determined with high statistical significance. Two different types of crystallizations are evident. A first at higher supercooling temperature exclusively consists of lithium disilicate crystals and a second at lower supercooling temperature consists of a mix of lithium metasilicate and quartz crystals. Increasing oxygen partial pressure shifts the probabilities of both nucleation types to higher temperatures and shorter times. It is assumed that under oxidizing conditions an increasing oxygen saturation coverage at the surface of the platinum alloy promotes crystal nucleation close to the three-phase boundary between oxidized metal, supercooled melt and furnace atmosphere.
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