Casting large silicon crystals in clear silica crucibles

Silicon crystals were cast by a directional solidification technique which uses a high temperature heat exchanger to extract heat from the bottom of the crystal. This method has been used effectively to grow sapphire crystals (up to 25 cm in diameter and weighing 30 kg). Silicon forms a tenacious bond with clear fused silica which results in cracking during cooling. Cracking can be limited to the outside surface by using thin walled crucibles. The heat-exchanger method has been used to produce silicon for use in solar cells. (FS)