Refractory Materials and Application
Magnetite refractories are chemically basic materials, containing at least 85% magnesium oxide. These are made from naturally occurring magnetite (MgCO3) and Silica (SiO2). The physical properties of this class of brick are generally poor, and their great value is primarily in their resistance to basic slags, particularly to lime and iron rich slags. These constitute the most important group of refractories for the basic steelmaking processes. In addition to metallurgical furnaces, basic brick are now being successfully used in glass tank checkers and in lime and cement kilns.
Chrome-magnetite material usually contain 15-35% Cr2O3 and 42-50% MgO whereas magnetite-chromite refractories contain at least 60% MgO and 8-18% Cr2O3. Chrome- magnetite refractories are used for building the critical paths of high temperature furnaces. These materials can withstand corrosive slags and gases and have high refractoriness. The magnetite-chromite products are suitable for service at the highest temperatures and in contact with the most basic slags used in steel melting. Magnetite-chromite usually has a better spalling resistance than chrome-magnetite.
Zirconia refractories have a very high strength at room temperature which is maintained up to temperatures as high as 15000C. Its thermal conductivity is found to be much lower than that of most other refractories. Zirconia also does not react readily with liquid metals and molten glasses. They are, therefore, useful as high temperature constructional materials for metallurgical furnaces and glass furnaces.
Monolithic refractory, the name generally given to all unshaped refractory products, are materials installed as some form of suspension that ultimately harden to form a solid mass. Monolithic refractories are replacing the conventional type fired refractories at a much faster rate in many applications including those of industrial furnaces.