Water is chemically-bound into the crystal structure of many minerals (e.g. clays, especially kaolins). In firing of ceramic bodies, this moisture is expelled during this phase. In the process of making calcined kaolin (meta kaolin) the reaction is considered finished at 600C.
Calcining is simply firing a ceramic material to create a powder of new physical properties. Often it is done to kill the plasticity or burn away the hydrates, carbonates, sulfates of a clay or refractory material.
|Temperatures||Hygroscopic water removed in clay bodies (50-250C-)|