Preparation of Pure Alkali Halide Crystals and Some of Their Properties

This paper describes some of the techniques that have been used successfully in this laboratory for the purification and preparation of a number of alkali halide crystals, particularly KCl. Measurements of the optical absorption, ionic conductivity, and thermal conductivity, are employed to test the purity of the crystals. Surface contamination of the zone-refined salt upon exposure to air, during handling between the different steps of preparation, appears to be a major source of contamination as judged by the ionic conductivity. A special apparatus has, therefore, been designed to permit both zone refining and subsequent seed pulling of the crystal to be carried out without changing the protective atmosphere.