Effects of cooling rate and oxygen partial pressure on heterogeneous crystal nucleation of supercooled lithium disilicate melt in PtRh20 containers

Publication date: 15 November 2019Source: Journal of Non-Crystalline Solids, Volume 524Author(s): R. Al-Mukadam, J. DeubenerAbstractLithium 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.
Source: Journal of Non Crystalline Solids - Category: Chemistry Source Type: research