Refractory brick of the alumina-silica group which contain more than about 45% alumina are known as high-alumina brick. Various grades of high alumina brick are available,including 50,60,70,80 and 90 percent alumina content. The terms sillimanite、 bauxite、 mullite or corundum brick, named by raw material or main mineral constituent, are also included in these classes. Because their higher refractoriness and higher alumina content, high alumina bricks do not vitrify or soften easily and provide great resistance to the attack of such fluxes as metallic oxides and alkalies. The advanced properties of high alumina brick, enable them to have greater service life than the best fireclay or silica brick in many applications.