GB1379231A - Method of growing crystals - Google Patents

Abstract

1379231 Growing crystals B A SECURITY SYSTEMS Ltd 22 March 1972 [24 Feb 1971] 5288/71 Heading B1G A crystal is grown by immersing a seed crystal in a saturated or near-saturated solution of the crystalline substance and maintaining the solution super-saturated by an amount such that the rate of growth of the crystal is below the optical growth rate, i.e. the rate at and above which defects arise in the crystal due to over-rapid growth. Super-saturation may be maintained by lowering the temperature or by evaporating off solvent. The weight of the substance deposited is preferably effected by (a) determining the surface area of the crystal (b) calculating the weight of substance to be deposited from solution over area (a) in a given time and (c) maintaing the solution supersaturated by such an amount that it will deposit weight (b) at a rate below the critical growth rate. In carrying out the method the crystal is mounted in a support wherein only one or a number of faces of the seed crystal may be exposed to the supersaturated solution, e.g. a major face which is a natural crystal facet. A suitable apparatus for carrying out the method is shown in the figure wherein vessel 1 contains saturated solution 2, and each seed crystal is mounted on a plate 3 positioned on an arm of a stirrer 4 driven by a motor 4' and a gearbox 5' at about 30 to 80 r.p.m. A rotating seal 7' is provided in lid 7 for stirrer 4 and the vessel 1 is surrounded by a jacket 5 which contains a heater 9 which controls the temperature of solution 2 by varying the air temperature in the space betwene 5 and 1. The crystals grown may be triglycine sulphate, or deuterated triglycine sulphate. The crystals may be used in infra-red radiation emission burglar alarms.