The energy contents of different polymorphous but chemically identical compounds in a system can be determined by comparing their heats of chemical reaction. The most instable form will have the highest heat of chemical reaction where as the most stable form will have the lowest heat of chemical reactions. Since generally the glass obtained by […]

Three naturally occurring important ceramic minerals of silicates of alumina have been intensively studied due to their prime importance in ceramic fields. They all have the formula Al2O3.SiO2 but differ in crystalline character and physical properties. The following are the three minerals:
1. Sillimanite
2. Andalusite
3. Kyanite
The important properties in ceramics for the three minerals studied were
1. The conditions under which […]

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 […]

A variety of clay containing alkalies gives up water at 360oC and 600oC on heating and at the same time preserves its micaceous habit. Muskovite is completely destroyed at 1100oC to 1200oC. Montmorrillinite does not change essentially in properties below 600oC. Later it loses its water of crystallization and undergoes conversion at 800oC to 850oC.
After […]

Different decomposition temperatures have been given for clays by different research workers. They are not easy to determine accurately because the rate of heating has pronounced effect. After the release of water from clay, it becomes a residual solid. The solid particles are closer together after the exodus of water which causes an overall shrinkage. […]

The water of constitution remaining in the clay is not completely removed even after drying and this is removed between a temperature range of 430oC to 600oC. When we heat the clay, the water is slowly expelled out accompanied by a slight contraction. The expansion curves for slowly heated clays shows that kaolin’s and most […]

The volume shrinkage can conveniently be measured by a simple form of dilatometer in which the loss of water can be read simultaneously from a balance.
Drying cracks and warping, the two important drying faults can be attributed to non-uniform shrinkage due to uneven distribution of water in clay. This uneven distribution can arise from temperature […]

If moist clay articles are dried by passing in between porous clays, it dries very fast. However the strength will be reduced. When dried clay wares are exposed to the air, moisture is taken up again and they become mechanically weaker.
The shrinkage associated with drying is not uniformly distributed over the article. It would be […]

In Brick manufacturing where the firing temperature is only 900oC to 1000oC maximum, the heat required for drying almost equals to the heat required for firing.
The mechanical strength of clay ware increases during drying and can be increased to the maximum extent by heating up to 300oC. The dry strength of clay increases with […]

The general assumption is that heat consumed in drying operation is very low. But it is not so, it is a wrong perception. The amount of heat consumed in drying operation is very high and it is in considerable amount. Since we are not seeing visible large fires, it is usually under estimated. A ceramic […]