Composition, Structure, and Thermal Properties of Potassium Acetate Hydrates

The crystal structure determines the properties of compounds and materials, although one can find simple yet industrially relevant compounds such as potassium acetate (KOAc) and its hydrates for which the properties and even the composition still remain misunderstood, owing to the lack of structural data. In this study, the crystal structures of KOAc polymorphs and hydrates were determined for the first time. The water content in the crystal hydrates was reliably determined revealing two new phases 3KOAc·2H₂O and KOAc·xH₂O (x = 0.38–0.44), instead of the “sesquihydrate” and “hemihydrate” that for a century were believed to be the main hydrated forms of KOAc at ambient temperature. The number and nature of phase transitions were clearly established, and the hydration–dehydration processes were studied in detail by variable-temperature X-ray diffraction and thermal analyses.