What is calcination as it relates to gypsum products?

Calcination, in the context of gypsum products, refers specifically to the process where heat is applied to gypsum (calcium sulfate dihydrate) to drive off water and convert it into other forms like calcium sulfate hemihydrate or anhydrite. This transformation typically occurs when gypsum is subjected to temperatures around 150°C to 180°C, causing the loss of chemically bound water. The result of this process is the formation of plaster of Paris, which is used in various construction applications.

The key aspect of calcination relevant to gypsum is the heat application and the subsequent release of water vapor. This chemical transformation is critical in the production of materials that harden after being mixed with water. The other options presented do not accurately describe the calcination process as it pertains to gypsum. For instance, while a severe combustion reaction involves significant heat and flame, it does not capture the essence of the water removal associated with calcination. Similarly, while gas release and physical changes in solid structure are relevant in other chemical processes or materials, they don't specifically align with the definition of calcination in gypsum products.