Effect of Organic Additives on the Structure and Morphology of Calcium Sulfate Hemihydrate Prepared Using Hydrothermal Method

Abstract Calcium sulfate hemihydrate (CSH) crystals are a high‐value‐added industrial material with broad application prospects. Effective control of CSH morphology is crucial to preparing high‐quality products and improving their performance. This study investigates the effect of citric acid, succinic acid, and polyacrylamide additives on the hydrothermal crystal growth and morphological evolution of CSH. CSH crystals are obtained in the presence and absence of these additives, and the products are characterized by X‐ray diffraction (XRD), Fourier‐transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). The XRD and FTIR results show that calcium sulfate dihydrate transformed into the hemihydrate form at the end of the hydrothermal process. SEM analysis reveals that citric acid led to the formation of prismatic crystals with reduced aspect ratios, while polyacrylamide resulted in thicker and irregular crystals. Additionally, fibrous need‐like CSH converted into regular prismatic crystals in the presence of succinic acid. In addition, thermogravimetric analysis coupled with FTIR is performed to investigate the thermal decomposition behavior and helped to understand the dehydration kinetics and thermodynamics of the CSH. The average activation energy calculated using the Friedman method is 35.02 kJ mol −1 . These findings demonstrate that additive‐assisted hydrothermal crystallization enables effective control over the shape parameters and morphology of CSH crystals.