1) Water Smoking Stage in Firing
In the ceramic bodies after completing all the process the firing process begins with the expulsion of the mechanical/physical combined water which is not removed by drying. The mechanical/physical water is nothing but the water used in the Shaping process of the ceramic articles. Most of this water is removed […]

In the form of artificial sillimanite bricks, Mullite is of great importance in industrial ceramics. kyanite is pre-fired, mixed with a bond of Clay and Alumina and shaped by Casting, Stamping, Pressing, Vibrating etc and fired at a temperature range of 1500oC to 1550oC. These bricks can be used upto a temperature of 1600oC under […]

When we fire the clay at high temperature the foreign oxides in the clay along with free Silica form a glass which can be detected by its transformation point in thermal expansion curves. This glass is responsible for the loss of in mechanical strength of fired clay at the softening point and the body deforms […]

The Mullite presence in ceramic materials is always regarded as a favourable advantageous property because it improves the product properties by its great hardness and low coefficient of expansion. The Mullite generation takes place between 1000oC and 1200oC after the producion of a glassy melt in the biscuit and it increases further between 1200oC and […]

Since all the fired clay contains high proportion of Silica it is obvious that its presence in the free Crystalline state must always be expected beside Mullite. The presence of Silica can be demonstrated by X-ray methods. The study on a dilatometer occasionally discloses a well developed Cristobalite effect at its conversion temperature of about […]

The heating effect on Kaolin may be followed by using Electron Microscope. Upto 1100oC we can not observe the breakdown of the hexagonal lamellae. Above 1100oC the fine needles begin to separate and that is the first nuclei of Mullite. When we heat it further we can observe the well formed needles of Mullite scattered […]

The excess Silica in the body materials acts as a strong flux. Clays which contain excess quantity of Silica easily sinters. Since the ceramic materials are not melted in the course of manufacturing, the Aluminum Silicates produced in them arise due to the result of reactions in the solid state. In slagged fire clay bricks, […]

The alumino silicates gained importance in the ceramic field not only as raw material for ceramic bodies but also as new materials often found in the fired wares, were they occur in the form of acicular crystals. They are usually felted together in a state of disorder and occur preferentially as local agglomerations. They were […]

Free silica in the form of cristobalite has been observed in the glass.
Sillimanite is most suitable as a raw material for refractory shapes, since normally it does not need to be pre-fired. With the transformation of other forms to mullite powerful stresses are associated which render pre-firing essential before using the minerals in the […]

The greatest heat evaluation was observed for andalusite followed by kyanite and sillimanite. Sillimanite is the most stable form of these minerals. All of them become instable on heating to a white heat. They are then transformed into a new silicate, 3Al2O3.2SiO2 which is called mullite, and a glassy melt.
Mullite is the most stable aluminum […]