GB707978A - Improvements in or relating to methods of growing crystals - Google Patents

Abstract

<PICT:0707978/III/1> Crystals, e.g. of ethylene diamine tartrate or lithium sulphate, are grown from seed immersed in a supersaturated solution of the salt by cooling (or heating in the case of substances such as lithium sulphate, which have a negative solubility/temperature coefficient,) the solution from one predetermined temperature to another, and then bringing the temperature back to its initial value while maintaining the solution supersaturated by passing it during this stage at an appropriate temperature through recharging apparatus containing solid solute. The cooling (or heating) and recharging steps are repeated until the crystals are the desired size. Limitation in size of crystals grown by the falling temperature method due to instability of certain solutions outside certain temperature ranges is thereby avoided. The Figure shows suitable recharging apparatus comprising a wide bore tube 2 containing solution 1 and solute 12 closed by end caps 3, the upper having a liquid inlet 4, a funnel 13 for introducing solid solute and the lower having a liquid outlet 4. A filter 10 is interposed between outlet and solute. The liquid inlets and outlets have enlargements 5 in which are thermometers 8. The temperature of the solution is controlled by heater 9 surrounding the tube 2 and auxiliary heaters 19, 20 surrounding tubes 17, 18 connected to the liquid inlet and outlet. A pump 21 draws solution from the tube 2 and feeds it to the growing tank through a tube 23 of heat insulating material having outlet holes 25, solution being withdrawn from the growing tank by the U tube 22. The flow of solution may however be in the reverse direction, the filter 10 then being at the top of tube 2. The time the recharging apparatus is connected to a growing tank may be much less than the time crystals are growing by the fall (or rise) in temperature and one apparatus may therefore serve a number of growing tanks. When the recharging apparatus is connected to a growing tank the saturation temperature of the solution in the tank is continuously measured by the apparatus described in Specification 684,042, [Group XX], and the temperature in the tank maintained about 2 DEG C. below (or above) the saturation temperature to keep the solution supersaturated. When not in use the tubes 22 and 24 may dip in another container for solution and the circulation of solution through the saturator maintained continuously. Specification 707,976 also is referred to.