Formation of α-Hemihydrate Inside of a Gypsum Crystal during the Dehydration Process

Gypsum (calcium sulfate dihydrate) is one of the most used inorganic binding materials in world. During calcination, calcium subhydrates are formed and, for technical reasons, mixed with water to form dihydrate again. Therefore, dehydration process gypsum and rehydration hemihydrate were investigated. This technically performed three different ways. Heating up, i.e., a rotary kiln, leads preferred formation β-hemihydrate, which crystallizes comparatively small crystals. Similar results can be achieved by recrystallization from slurry around 100 °C an autoclave or under steam atmosphere. However, contrast, here larger, needle-like morphology sometimes branched α-hemihydrate The synthesis β-hemihydrate was investigated detail special thermal stage optical microscopy on natural single It observed that crystal loses transparency because breaking surface crystals due evaporation. Furthermore, within deeper layer crystal, new become visible but disappear during upper layers. These expected α-hemihydrate. theory inside experimentally proven present work. work firstly shows crystallization alpha-hemihydrate.