Doped Tungsten Doubles lifetime in Sapphire Growth
Plansee has used a novel material to prolong the lifetime of heaters used in the high temperature growth of sapphire boules used in LED manufacturing Plansee uses the creep-resistant tungsten material 'WVM' to manufacture heaters for sapphire growth. These have more than twice the service life of conventional tungsten heaters. Sapphire growth takes place at high temperatures of approximately 2100 ¡ãC. In the Kyropoulos process, rod heaters made from pure tungsten are generally used. These often have to be replaced after just a few cycles. This is due to the high level of embrittlement and deformation. It can sometimes be so extreme that the heater rods touch the shielding and cause short-circuits. To meet the needs of single crystal growth applications, Plansee has further developed a material that has already earned the plaudits of the lighting industry for its behaviour at high temperatures. The material consists of pure tungsten with very low quantities (30-70 ppm) of potassium. The creep resistance of this material is several times better than that of pure tungsten. This capability was recently confirmed by a sag test performed by Plansee's materials engineers. Putting WVM to the test The scientists at Plansee simulated the use of its novel material at high temperatures and under various mechanical loads. The sag test proved that WVM sags four times less than pure tungsten. This is because potassium leads to a more stable and coarser crystalline structure than pure tungsten. This property also has a positive influence on the material's creep resistance. The graph below compares the sag for pure tungsten and WVM.
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