t is a general term for products of magnesite and other magnesia raw materials which have reached sintering degree after high temperature treatment. The magnesia produced by using natural magnesite as raw material is called sintered magnesia by one-step or two-step calcination process of high-temperature equipment such as shaft kiln and rotary kiln; the magnesite formed by using magnesite as raw material through arc furnace melting to reach melting state and cooling is called electromelted magnesia; and the magnesia produced by extracting magnesium oxide from seawater is called seawater magnesia. Magnesia is one of the most important raw materials for refractories. It is used to manufacture various magnesia bricks, magnesia-alumina bricks, ramming materials, furnace feeding materials and so on. Containing more impurities, it is used to pave the bottom of the steelmaking furnace, etc.