What are the properties and application characteristics of magnesia ceramics

       Magnesium oxide (MgO) is an alkaline oxide with a high melting point, with a melting point of up to 2820 degrees Celsius, which is higher than that of zirconia. Its density is 3.58g/cm3~3.60g/cm3, Mohs hardness is 5~6, thermal expansion coefficient is 14.3X. It has high resistivity and high dielectric constant at high temperature, and is a high-temperature insulating material with excellent performance. It also has excellent resistance to molten metal erosion and alkali slag erosion, and is the main component of alkali refractories for high temperature.

    Magnesium oxide has an equiaxed cubic crystal structure. As a stabilizer for zirconia modification, the incorporation of magnesia into zirconia crystals can transform the crystal form of zirconia from m to t. When the amount of magnesium oxide added is 20%~30%, the zirconium oxide crystal zirconium crystal can keep the crystal form stable at different temperatures, especially during high thermal cycles. Therefore, magnesium zirconate ceramics (MSZ) have excellent high temperature resistance, thermal shock resistance, low thermal conductivity, high thermal insulation, and stable high temperature chemical properties. However, like calcium oxide, it has a high vapor pressure and is volatile in the high enthalpy of the plasma spray jet, which favors the air gap in the coating, which affects the density and stability of the coating.

    Magnesium oxide volatilizes very quickly at 2400°C to 2500°C. It is also difficult to form a magnesium oxide coating under the conditions of rapid heating and quenching cooling of the plasma flame. In order to improve its spraying process performance, the magnesium oxide powder can be coated with silicon oxide to prevent the volatilization of magnesium oxide at high temperature, which can greatly improve the deposition efficiency of the powder. The addition of silicon oxide can reduce the melting point of magnesium oxide. Nevertheless, magnesia containing 7% silica still has a higher melting point than alumina.

Because magnesium oxide does not undergo crystal transformation, and has good melt corrosion resistance and high temperature insulation performance, at the same time, the bonding strength of magnesium oxide coating and steel substrate is higher than that of ordinary ceramic coatings, so it is It will be used as a basic refractory oxide coating in industry, especially metallurgical industry.