The Role of Sintering in the Synthesis of Luminescence Phosphors

The phenomena of calcination, roasting and sintering are closely related and often used intermittently. Calcination is the process of subjecting a substance to the action of heat, but without melting or fusion, for the purpose of causing some change in its physical or chemical constitution. The objects of calcination are usually: (1) to drive off water, present as absorbed moisture, as "water of crystallization," or as "water of constitution"; (2) to drive off carbon dioxide, sulphur dioxide, or other volatile constituent; (3) to oxidize a part or the whole of the substance. The process of calcination derives its name from the Latin calcinare (to burn lime) due to its most common application, the decomposition of calcium carbonate (limestone) to calcium oxide (lime) and carbon dioxide in order to produce cement. In roasting, the minerals impose heartburn, which is used to drive out volatile components whereas in sintering, small pieces of ore or powder are heated to make bonding. Sintering is a method for making objects from powder through agglomeration by heating the material in a furnace to 80-90% of its melting point until its particles adhere to each other. It is known as solid state sintering. The clay particles sinter even before they actually begin to melt into a glassy state (vitrification). The production of powder metal components can be summarized in three steps; powder preparation, compaction and sintering.