calcined

Calcined refers to a material that has undergone calcination, a thermal treatment conducted at high temperatures to bring about decomposition, phase change, or loss of volatile constituents, such as water or carbon dioxide, without melting the material. The process is typically carried out in kilns or furnaces and may occur in air or in a controlled atmosphere. The word calcine comes from the Latin calcinare, meaning to burn lime.

The primary purpose of calcination is to remove bound water or other volatile components and to drive chemical changes that convert hydrates or carbonates into oxides or other a­­nhydrous forms. Temperature ranges vary by material: hydrated minerals may dehydrate around 100–600 °C, carbonates such as calcium carbonate decompose around 800–1000 °C (producing oxide and CO2), and clays can be dehydroxylated to form calcined clays like metakaolin. In cement manufacture, calcination of limestone to produce lime is an essential preliminary step, after which further high-temperature processing forms clinker.

Calcined materials find wide use. Calcined limestone yields quicklime for construction and chemical processes; calcined gypsum forms plaster of Paris for plastering and molding; calcined clays and alumina serve as reactive bases in cement and ceramics. The term also applies to materials like calcined coke and calcined clays used as catalysts or supplementary cementitious materials. The process is energy-intensive and raises considerations related to CO2 emissions and dust control, depending on the material and scale.