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 […]
Drying shrinkage and apparent specific gravity of the dry ware increases with rising surface tension. But the water content at the critical point and the speed of drying are lowered. When the surface tension is increased the so called secondary shrinkage which takes place beyond the critical point reduces and the drying speed falls over […]
Infra-red radiation is also utilized for drying of ceramic articles. The infra-red radiation is largely reflected or transmitted by ceramic materials, where as water adsorbs it and converts it into sensible heat. Special lamps with comparatively low filament temperature radiate 80% of their energy in the infra-red.
This type of drying is suitable for green ware […]
In the first stage, the ware is warmed from 20oc to 45oc and the relative humidity of the air is maintained at 85%. In the second stage the relative humidity is lowered from 85 to 75%. In the third stage it is reduced to the maximum extent possible and at the same time the temperature […]
