Molybdenum and tungsten in sapphire crystal growth industry
High-temperature refractory metals such as molybdenum- and tungsten-based materials are essential in today’s sapphire crystal growing technologies and are widely used for crucibles, hot-zone shieldings or heaters. The worldwide sapphire production capacities are dominated by the three growing methods Kyropoulos process, heat-exchange method and edged-defined film-fed growth. The key for economic success of all these methods lies in high-quality, large-size crystals while keeping production costs as low as possible. Consequently, performance and lifetime of high-melting metal components are crucial for cost reduction in this competitive market.
The paper gives a broad insight into high-temperature characteristics of molybdenum, tungsten and their alloys. The discussion focuses on mechanical and thermo-physical properties, and on interactions of liquid alumina with refractory metals at 2100 °C. We propose MoW as an interesting alloy with high creep resistance and modified thermo-physical behavior. Additional efforts on conditioning refractory metal surfaces in contact with melts could boost particularly crucible lifetimes.