Production of Sapphire
In the part 2, we introduce 3 methods of production of sapphire.
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It's a method really similar to The Czochralski method, but a crystal is grown up by lowering the temperature of the melt slowly. Do not perform the pulling up of crystal, ( it may perform pulling up at slow speed in some cases ), a crystal is grown in melt. Therefore , crystallization is rarely exposed to atmosphere, and that is easy to get a high crystal of the quality future because it is hard to receive thermal stress. Like the Czochralski method, growth in the c-axis direction is difficult but the reduced production cost of wafers come to be produced in Russia.
Melting crucible (Heat Exchange Method)
The inventor Fred Schmid worked for the Army Research Laboratory in the State of Massachusetts.
He was requested by the US Army to develop a large sapphire for infrared sensor window of military aircraft sidewinder missile (air to air missile).
He took on that research work for large sapphire window.
The process requires that you place a molybdenum crucible in the center of a large vacuumed furnace, and set a seed crystal in the central bottom of the crucible. Sapphire crackle is loaded on top of the seed crystal, filling up the crucible with sapphire crackle and close by cover. The furnace is then heated up to the melting point of sapphire around 2050 Deg-C by heater which surrounds the crucible. At this time, in order to prevent melting of seed crystal, blowing Helium gas from outside of the crucible and exchange the seed part by helium gas. So, this method is called Heat Exchange Method. According to Fred Schmid’s research report, he has successfully achieved the large-sized sapphire cylinder of which
18.4 cm in diameter, 13.3 cm in thickness and over 15.2 kg in weight.
The EFG Method
The EFG method (Edge-defined Film-fed Growth) was reported by Labelle in 1971 and others. The slit called Die is inserted into a crucible, and raise the melt which rose to the die tip and crystallize it.
Because the crystal succeeds the tip shape of the die and grows up, it can get any cross-section.
Because can grow up a plate having a c-plane difficult as for several pieces by the Czochralski method at a time, the feature is that is advantageous to reduction in cost.
There are more information about artificial sapphire in Adamant Namiki Precision Jewel Co., Ltd. website.
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