Patent GB-707976-A (GB)
Title: Improvements in or relating to apparatus for use in growing crystals
IPC: C30B7/00
Filed: 1950-05-22
Abstract: Apparatus for growing crystals from a supersaturated solution comprises a heated tank for the solution, thermostatically controlled, a seed crystal support in the tank, a recharging column into which solid supply material can be introruced and having filters to prevent escape of the solid and means for applying heat uniformly along the length of the column, a pump for circulating the solid between the tank and recharging column, and tubular connections between the tank, pump and column, two of the connections, between the column outlet and tank return and immediately after the tank outlet, being heated to control the temperature of the solution entering and leaving the tank and column.  As described the apparatus comprises a growing tank 1 containing a rotatable crystal support comprising a shaft 11 from which project arms 20 supporting annular plates 10 with inward and outward radial projections 25, 26 (Fig. 3). Seed crystals 27 are mounted on the plates in the positions shown by means as described in Specification 702,526.  The shaft 11 is secured by a screw 16 to a shaft 12 mounted in a bearing in the lid 4 of the tank 1, the shaft 12 being rotated first one way and then the other by an electric motor driving the bevel gear 14.  The lid 4 has a viewing window and a window for admitting light into the tank.  The lid is <PICT:0707976/III/1> <PICT:0707976/III/2> <PICT:0707976/III/3> <PICT:0707976/III/4> removable to enable the crystal assembly to b introduced into or removed from the tank by the method described in Specification 707,977.  The tank has a dished bottom to hinder spurious seeding at the circumference and to assist collection of seeds so formed into the centre of the base of the tank.  The tank is heated by an electric heater underneath, fed from an adjustable autotransformer controlled by a motor the direction of rotation of which is controlled by a thermometer 30 immersed in the tank. When this direction changes a sudden change also occurs in the current in the heater, to cause a definite start to the process of raising or lowering the temperature.  The control operates over a small temperature range only, the tank temperature being substantially constant.  A small electric lamp is positioned in the tank adjacent to the thermometer to increase the sensitivity of the control, the lamp being energized when the tank heater voltage is increasing.  The recharging column or saturator of the apparatus comprises a wide bore tube 57 containing solute 58 supported on a porous filter 59.  The top cover 67 for the tube has a central opening, normally closed by a bung 74, for introducing solute, and a channel 69 with thermometer chamber 71 for introducing or withdrawing solution.  The bottom cover is similar but has no central opening.  A pump 55 circulates solution through the growing tank and saturator, the solution preferably passing down the saturator.  If the solution circulates in the opposite direction the filter is fitted at the top of the saturator. Heaters 56 and 60 control the temperatures of the solution entering and leaving the saturator and ensure that no crystallizing occurs in the conduits.  The heater 56 is as close as possible to the tank 1 and comprises a wire resistance wound round one stem of a U tube dipping into the tank.  The saturator is maintained at a constant temperature above or below that in the tank 1, depending on whether the temperature/solubility coefficient of the solute is positive or negative, by an octagonal hot air enclosure provided with thermostatically controlled heaters.  Specification 684,042, [Group XX], also is referred to.  The Provisional Specification describes a saturator having the inlet and outlet formed from U tubes and having a funnel for adding solute.  The return to the tank is made of p "Tufnol" (Registered Trade Mark).  Specification 683,971, [Group XXIII], also is referred to in the Provisional Specification.