Experimental techniques for identifying operating variables of crystal growth and nucleation—From readily soluble salts to sparingly soluble salts

The classical experiments performed by McCabe and his co-workers confirmed several important operating factors that influence the secondary nucleation (contact nucleation) rate and crystal growth rate, such as supersaturation, temperature, impact energy, and contacting material for readily soluble salts, using the single crystal technique. The key to success is that the experiment was designed by varying an operating variable while keeping the others constant. Following the same strategy, a pH-stat, or constant-composition system, was constructed in our laboratory for investigating the crystallization and precipitation of sparingly soluble salts. The supersaturation and pH were carefully controlled using an autotitrator so that the factors affecting crystal growth and nucleation were identified, including supersaturation, pH, ionic strength, species ratio, and impurities. The nucleation and crystal growth behaviors exhibited by the readily soluble and sparingly soluble salts were then compared.