A COMPARISON OF SECONDARY NUCLEI PRODUCED BY CONTACT OF DIFFERENT GROWTH FACES OF POTASH ALUM CRYSTALS UNDER SUPERSATURATED SOLUTIONS

Secondary nuclei of potash alum crystals may easily be produced by gen tle crystal contact. In this investigation, crystal faces of the {100} , {110} and {111} families were identified in a parent crystal, and ge ntle contact between these and a solid surface in a slightly supersatu rated solution of potash alum produced many secondary nuclei of the sa me orientation. Breeding of the large number of particles produced by contact between a parent crystal and a glass surface under supersatura ted aqueous solution was directly observed by optical microscopy with an in situ, thermostatic cell. A strong correlation was found between the symmetry of the nuclei produced and that of the parent crystal fac e. Ex situ scanning (SEM) and transmission electron microscopic (TEM) measurements were also carried out to study this type of secondary nuc lei. produced from a known surface geometry. In these cases, many smal l nuclei in the size range of 50 nm to 1 mu m were produced and studie d. The larger crystals displayed morphologies commensurate with that o f the parent face; the very small nuclei, whilst frequently showing ve ry poorly ordered boundaries, nonetheless were highly ordered internal ly, as shown by electron diffraction, the symmetry observed reflecting that of the parent face.