Kinds of refractory materials

Refractory materials can be divided into three groups, i.e. a) insulation materials, b) refractory concrete and mortar and c) refractory bricks. The last group is not discussed in this paragraph but in a later one. 

We distinguish two kinds of insulation materials fibre materials and insulation bricks. I received information on this subject from the American firm BNZ Materials Inc. and its Dutch subsidiary INSULCON. They manufacture insulation bricks which are called Marinite. 

Insulation materials contain more air and have an lower apparent density than ordinary refractory materials. In the case of insulation bricks the desired porosity is obtained by making use of additives which produce gases when heated (e.g. calcium carbonate), or of porous raw materials. In figure 11.3. 2 the effect of the appplication of insulation bricks is represented. 

In figure 11.3. 2, X (the Greek letter lambda) stands for the heat conduction coefficient. This is part of the following formula in which (p (phi) stands for the heat current through the brick. 

A is the area through which the heat current passes, dT is the temperature difference between the outer and inner walls, dx is the thickness of wall 

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