What are the properties and application characteristics of alumina-silica composite powder

       Alumina-silicon oxide (Al2O3-SiO2) composite powder is a ceramic coating material based on alumina containing a certain amount of SiO2. The addition of SiO2 significantly reduces the melting point of the coating, which is in the state of glass or enamel. The coating is very dense and the porosity is greatly reduced. Since SiO2 is a strong acid oxide, the coating has excellent acid resistance.



   According to the content of Al2O3 and SiO2, Al2O3-SiO2 composite powder is mainly divided into mullite powder, mullite powder, refractory cement powder and so on.

   Coatings can be prepared by gas-stabilized plasma spraying, flame spraying, explosive spraying and other processes.

  1) Mullite powder

    Mullite is an acidic refractory material composed of alumina and silica, with a molecular formula of Al2O3·SiO2, containing 71.80% alumina and 28.20% silica. The melting point is 1830℃, and the thermal expansion coefficient is 4.5X10-6K-1 (20℃~1300℃).

    The mullite coating is pink and vitreous, and the coating is very dense. It has excellent corrosion resistance, especially good acid corrosion resistance, and can resist the corrosion of most acids (including hydrofluoric acid), but not alkali liquid corrosion ; Can resist high temperature erosion of many kinds of metal melts and acid slag corrosion, but not resistant to alkali metal, alkaline earth metal melt and alkaline slag corrosion. It is suitable for use in acid medium corrosion and wear conditions, and can also be used to prepare thermal barrier coatings, high temperature oxidation protective coatings, insulating and dielectric coatings.

    Coatings can be prepared by gas-stabilized plasma spraying, flame spraying, explosive spraying and other processes.

  2) Mullite powder

      Mullite is also an aluminosilicate ceramic material composed of Al2O3 and SiO2, but its composition is not fixed, and its alumina content is between 72% and 78%, which is equivalent to the molecular formula 3Al2O3 2SiO2 or 2AI2O3 SiO2. The melting point is 1810℃~1830℃, and the thermal expansion coefficient is 4.5x10-6K-1 (20℃~1300℃).

    Similar to mullite coatings, mullite coatings have excellent corrosion resistance. It is also suitable for the preparation of acid medium wear-resistant coatings and insulating coatings.

    Coatings can be prepared by gas-stabilized plasma spraying, flame spraying, explosive spraying and other processes.

  3) Refractory cement powder

    Refractory cement powder is a thermal spray powder made of mineral raw materials such as high alumina refractory clinker or corundum fire mud commonly used in the metallurgical industry. Its cost is low, but its composition is relatively complex, so that the composition and performance of the coating are not the same.

    This coating has very good heat resistance and oxidation resistance, has good wetting ability to steel substrates, etc., has relatively strong diffusion and penetration ability on the surface of refractory furnace lining, and has good adhesion to matrix materials. It is often used as a Heat-resistant and anti-oxidative protective coatings for steel base materials and repair materials for crucibles and furnace linings.

   Coatings are mostly prepared by powder flame spraying process.