Quality Requirements of Kaolin for Refractory Materials

The quality requirements of kaolin for refractory materials are not very strict, but the change of the ratio of alumina and silica content in kaolin directly affects the change of refractoriness.

The values of alumina and calcium silicate in high-quality kaolin are generally between 0.7-0.8 or slightly higher. The ratio of alumina to silica in pure kaolin is 0.85. When the ratio is bigger than 0.85, rich aluminum minerals exist and the refractoriness increases. When it is less than 0.7, the content of kaolin is low, quartz is present, and the refractoriness is reduced. In addition, the high content of iron oxide, titanium oxide, and potassium oxide in kaolin will reduce the refractoriness, which is harmful.

There are two main types of kaolin clay used as refractory material products :refractory bricks,silica-alumina-bulk. The former is the refractoriness not less than 1730 degrees Celsius, the 2*105Pa load softening starting temperature is not less than 1350 degrees Celsius, and the re-sintering line shrinkage is less than 0.5% (1400C, 2H)Various sizes and shapes of refractory bricks can be made as required. The latter is a lightweight, fire-resistant insulation material manufactured using kaolin, calcined at 1000-1100C, and then melted with a 2000C electric arc furnace to tell it to remain blown to make bulk.

In China, clays with refractoriness greater than 1580 degrees Celsius and bauxite mines with refractoriness greater than 1770 degrees Celsius are commonly referred to as fire-resistant clays.

The former is divided into hard clay, soft clay, semi-soft clay, and the latter is called high alumina clay. Some colored kaolin cannot be used for ceramics and paper, but it is a good raw material for refractory materials. Therefore, refractory materials is an important market for comprehensive application of kaolin.