Magnesia (MgO, magnesia) is a basic refractory ceramic distinguished by its high melting point (2852 °C) and resistance to basic slags and alkaline environments that decompose acidic refractories like alumina and silica.
It is widely used in steel-making (linings, tundish nozzles), non-ferrous metal casting (brass, bronze furnaces), and as a substrate or breaker ring in electrically heated furnaces. Its high vapour pressure above 2000 °C limits continuous use in vacuum, but in atmospheric-pressure basic-service applications it is often the most economical choice.