Alumina-Silica Composite

This composite is a very common refractory material. Due to easy availability and low cost aluminia-silica composite is widely utilized in industry today. The percentage composition may vary from pure alumina to pure silica. Fireclay is built with alumina varying from 20 to 40%. Between these limits of alumina and based upon degree of firing four classes of fireclay are obtained. They are super duty, medium duty, high duty, and low duty. Fireclay is used in form of bricks. Pure silica brick is typically acid. In composite of silica-alumina the acidic nature changes to neutral with enhancing proportion of silica. Acidic fireclay along high alumina content between 50-99% has high fusion temperature than fireclay bricks. They are utilzed for more severe furnace condition. The acidic fireclay bricks are more costly.

Basic refractories consist mostly of magnesia (MgO) lime (CaO), chrome ore or mixture of two or more of these materials. Basic bricks have greater density, high melting point temperature & good resistance to chemical associated by basic slag and oxides. These refractories, having 92 to 95% magnesia are utilized as linings in the basic oxygen steel making furnace. Though, refractories are costlier.