GB1385234A - Crystal growing - Google Patents

Abstract

1385234 Computerized crystal growth WESTERN ELECTRIC CO INC 6 April 1972 [7 April 1971] 15932/72 Heading B1G A synthetic crystal is grown from a seed crystal supported in an upper zone of an elongated vessel and a crystal growing nutrient solution provided in the lower zone of the vessel by applying heat to the upper and lower zones to establish a convective flow of dissolved nutrient over the seed crystal with a temperature gradient existing between the upper and lower zones and controlling the temperatures in the zones thereby controlling the rate of flow of the nutrient solution over the seed crystal. The temperature control conditions are obtained from an empirical formula which has been reduced to a finite number of steps and such steps as an algorithm are fed into a computer which automatically controls the temperatures in the two zones. Figure 1 shows a crystal growing apparatus 100, comprising a cylindrical autoclave 101 supported on fire brick 102 and set in a concrete pad 103. The autoclave is divided by perforated baffle 104 into two zones. In the lower zone the nutrient to be dissolved e.g. quartz is contained in a wire basket 106 whilst in the upper zone a wire rack 108 supports a plurality of seed crystals 109. In operation the interior of the autoclave contains aqueous media e.g. a solution of sodium hydroxide and one or more dopants e.g. lithium nitrate. Heating is provided by heater bands 112 and 113, and current supplied to these heaters can be individually adjusted by the magnetic amplifiers &c shown in Figure 15 and controlled by digital computer 142 which comprises a central processing unit 151, coupled to a memory storage device 152 and control circuit 153. The apparatus also includes a pressure sensing device 114 positioned in the autoclave via an aperture in threaded seal 111, to permit pressure monitoring during the crystal growing process. The temperature in the heater bands is monitored by thermocouples 116, 117, 118 and 119. The entire autoclave is enclosed in a thermal insulating jacket 122. In operation the temperature difference between the upper and lower zones is about 70‹F, and the pressure in the autoclave approximately 25,000 pounds per square inch. The apparatus is preferably used for the growth of quartz crystals but may be used for emerald, corundum (Al 2 O 3 ), berlinite (AlPO 4 ), calcite (CaCO 3 ), zincite (ZnO), tourmaline, magnetite, fluorite, scheelite, garnets and zircons.