corundum, synthetic corundum.7, Seiko, floating zone, gems

Floating-zone crystal growth was first devel-oped in 1953 to produce high-purity silicon as a semi-concluctor. It has since becn used to produce refractory mctals, alloys, and other sen~iconductingcompounds. Although colorless synthetic sapphire has been grown by this method in the past, it was not until thc Suwa Seikosha (SeikoWatch)Company Ltd. of Japan, became involved, as part of their efforts to make a better elec-tronic crystal for their watches, that this technique was developed to produce synthetic gems. 111 thc floating-zone crystal growth process, a sin-tcrcd rod, composed of a uniform mixture of all of thc coinponcnts necessary to producc thc dcsired gcin material, is held vertically at both thc top and bottom. An infrared radiation convcrgcnce heater, using a halogen lamp and an ellipsoidal reflector with its inncr surfacc gold plated, hcats a small region ncar the top of thc rod until it melts. The two holdcrs thcn bcgin to rotate whilc at the same timc the hcat source begins dropping down the rod at an cvcn rate. Eventually, the sintered rod is consunled and a single crystal results.