Refractories are commercial products created from nonmetallic minerals that possess the capacity to maintain their form and strength when subjected to highly elevated temperatures amid varying extremes of mechanical stress and chemical attack by hot gases, liquids, or molten and semi-molten substances. In the modern economies of the world, alumina (Al2O3), the oxide of aluminum, is the principal ingredient of a significant number of the products used in these high – temperature industrial applications. The alumina content of a particular refractory may range from 30% to 100%, depending on the nature of raw material employed to produce the refractory product.
General Specifications
The principal aluminum hydroxide minerals found in varying proportions within bauxite are: gibbsite, Al(OH)3; boehmite, AlOOH; and diaspore, AlOOH.
The bauxite used for producing abrasive, chemical, and refractory products must fulfill much more rigid compositional requirements than the crude ore that is commonly used for aluminum metal production, as shown in Table II. The natural chemical impurities that exist within these raw materials are not chemically removed from the ore during product processing, as in the case of metallurgical grade bauxite, where impurities are eliminated through a caustic leaching method that is known as the Bayer process. These specialty ores are utilized in an essentially unrefined form, as direct feedstocks for the production of their ultimate end products.
A number of tests are customarily applied to calcined bauxites to assess their suitability for use as a refractory raw material. Primary among these physical tests are: determination of pyrometric cone equivalent (PCE), a measure of the material’s softening or deformation temperature; measurement of bulk specific gravity; and calculation of apparent porosity.
