At about 900oC to 1000oC an exothermic reaction takes place while heating the clays. Two reactions are considered possible causes of the evolution of heat.
1. Conversion of alumina from the gamma to alpha form.
2. Combination of gamma alumina and silica to form sillimanite or mullite.
It takes place with strong evolution of heat. The second reaction is theoretically possible, since the exothermic character of Sillimanite formation from the oxides.
By determining the strength of porcelain body at different firing temperature a good insight into the reactions occurring during firing has been observed.
To be contd……..
