Authorities differ on the meaning of Calcination (also referred to as calcining). The IUPAC defines it as 'Heating to high temperatures in air or oxygen'. However calcination is also used to mean a thermal treatment process in the absence or limited supply of air or oxygen applied to ores and other solid materials to bring about a thermal decomposition, phase transition, or removal of a volatile fraction. The calcination process normally takes place at temperatures below the melting point of the product materials. Calcination is not the same process as roasting. In roasting, more complex gas–solid reactions take place between the furnace atmosphere and the solids. Calcination takes place inside equipment called calciners. A calciner is a steel cylinder that rotates inside a heated furnace and performs indirect high-temperature processing (1000-2100 °F) within a controlled atmosphere.

 

The calcined products were obtained by calcining ammonium paratungstate(APT) at different phase transition temperatures and then reduced to tungsten powder under hydrogen atmosphere in reducing furnace. The micro-morphology and particle size distribution of the reduced tungsten powder were analyzed by scanning electron microscope(SEM) and laser granulometer,respectively.The results show that the calcination temperature for APT has a great effect on the tungsten powder properties.The tungsten powder with uniform particle size and good dispersity can be obtained at the calcination temperature of 425 ℃.