Wednesday, April 6, 2011

Calcination

Definition:
The process of heating a substance to a high temperature but below the melting point or fusing point causing loss of moisture reduction or oxidation and dissociation. Into simpler substances, the term was originally applied to the method of driving off carbon dioxide from limestone to obtain lime.

Calcination is also used to extract metals from ores.

Or

To heat a substance to a high temperature but below the melting point or fusing point causing loss of moisture, reduction or oxidation and the decomposition of carbonates and other compounds.

Explanation:
Calcination also referred to as calcining a thermal treatment process applied to ores and other solid materials in order to bring about a thermal decomposition phase transition or removal of a volatile fraction. The calcinations process normally takes place at temperatures below the melting point of the product materials.

Calcination is to be distinguished from roasting. In which more complex gases, solids reactions takes place between the furnace and the solids.

Calcination reactions:
Calcinations reaction usually takes place at or above the thermal decomposition temperature or transition temperature. This temperature is usually defined as the temperature at which the standard energy of reaction for a particular calcination reaction is equal to zero.

Example:
Examples of chemical decomposition reactions common in calcination processes and their respective thermal decomposition temperature include
CaCO3 = CaO + CO2 : 484ÂșC

Occurance:
Calcination occur under layers of hot volcanic ash.

Physical properties:
The physical properties which involves bulk density, total pore volume, and the pore size distribution of the calcines prepared under different conditions were determine by using a Mercury porosimeter.
It was found that the physical properties of calcines were dramatically affected by the calcinations conditions, at high calcination temperature, because of sintering and shrinking affects, a decrease in properties. An increase in bulk density and average pore radius were observed.
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