New insight into the salt role during preparing α‐hemihydrate gypsum in atmospheric salt solution: Particle size control

Abstract The synergistic control of the crystal morphology and size of α‐hemihydrate gypsum (α‐HH) was achieved by adjusting the Na 2 SO 4 concentration and maleic acid content. Maleic acid primarily regulated the α‐HH morphology through surface adsorption. The concentration of Na 2 SO 4 determined crystal size by tailoring the maximum relative supersaturation ( S max ) during α‐HH crystallization. Higher Na 2 SO 4 concentrations led to higher S max and smaller crystal sizes. The S max of α‐HH in a 9% Na 2 SO 4 solution was 4.5 times that in a 6% solution, resulting in a significant decrease in crystal size from approximately 40–18 µm as the Na 2 SO 4 concentration increased from 6% to 9%, while maintaining similar crystal morphology (average aspect ratio of about 1.0). This study filled the gap in research on particle size control during the preparation of α‐HH using the salt solution method under atmospheric pressure, contributing to a more systematic and comprehensive understanding of this method.