GB653737A - Improvements in or relating to method of growing crystals - Google Patents

Abstract

Crystals are grown in two stages: in the first stage seed bodies cut from crystals of the material-to-be-crystallized are planted in a solution of the material and the solution is caused to flow relative to the seed bodies while the temperature is progressively lowered; all the seed crystals thereby grown are removed from the solution and inspected, and only the sound crystals are replanted in solution for the second stage of growth. In the growth of ammonium dihydrogen phosphate and its isomorphs, the yield of sound full-size crystals obtained by this two-stage process is greater than in prior one-stage processes. In an example, seed plates 5 (Fig. 3) cut from crystals of ammonium phosphate with the larger sides <PICT:0653737/III/1> <PICT:0653737/III/2> <PICT:0653737/III/3> <PICT:0653737/III/4> 1.5 inches long, are mounted in a tray 7 (Fig. 5), which is rocked back and forth on a fixed axis, as indicated by the double-arrow, in a chamber (not shown) through which warm air is circulated. An aqueous solution (saturated at 36 DEG C.) of ammonium phosphate at a temperature of 38 DEG C. is introduced into the preheated tray; and the temperature of the circulating air is then gradually lowered to normal room temperature during about 8 days. The crystals thereby grown are removed from the tray, and those which have a clear pyramidal shell 11 (Fig. 4) on one or both ends are replanted with suitable spacing (Fig. 6) for growth into full-size crystals. In this second stage the initial temperature of the solution is about 41 DEG C., and the growing-time is about 45 days. The two-stage process of crystallizing makes possible the use of addition substances in the first stage, which would be deleterious to the product in a one-stage process. Specification 653,736 is referred to.