Recent experiments on crystal growth in gels

Abstract

The paper gives an account of recent experiments on nucleation and crystal growth in gels and their relationship to crystal size and perfection, with special reference to calcium tartrate, lead iodide and silver iodide. Because the crystals in any one system grow competitively, nucleation is a key issue which, in all likelihood, governs the practical utility of the technique as a whole. Its limitation is believed to be the principal function of the gel. Heterogeneous nucleation is possible, but is substantially suppressed by the protective character of the medium. Moreover, there is evidence that a large number of the macroscopic crystals obtained owe their existence to “homogeneous” nuclei, rather than foreign substrates. The significance of pH and other factors which affect solubility has been explored and an attempt made to distinguish between the conditions which affect nucleation and those which affect growth. The conclusions are believed to have general validity, but for complete reliability each system must still be investigated in its own terms. The gel method is capable of yielding crystals of high optical perfection, of a variety of materials which have so far resisted orthodox growth techniques.