Growth kinetics of ammonium‐ and potassium‐dihydrogen phosphate crystals

Growth rates of ammonium‐ and potassium‐dihydrogen phosphate crystal faces have been measured in a simple laboratory apparatus under carefully controlled conditions of temperature, supersaturation and solution velocity. The growth process, which was found to be second‐order with respect to the supersaturation, is considered to be controlled by surface reaction. Growth rates of the ammonium salt (ADP) are much higher than those of the potassium‐salt (KDP) under equivalent conditions. It is suggested that this is due to the occurrence of hydrogen bonding between ADP molecules, which give larger integrating units (thicker growth layers) than occur with KDP.