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.At the 19th Plansee Seminar Dr. Michael Mark, Dr. Hannes Traxler, Robert Schiftner, Dr. Bernd Kleinpaß and Dr. Wolfram Knabl gave a broad insight into high-temperature characteristics of molybdenum, tungsten and their alloys. The discussion focused on mechanical and thermo-physical properties, and on interactions of liquid alumina with refractory metals at 2100°C. They proposed 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.

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