Ceramic Protective Coatings for Cordierite-Mullite Refractory Materials

The issue of cordierite-mullite refractories protection from the influence of aggressive factors is considered. The interaction between the components of protective coatings has been studied. It has been investigated that in the systems based on poly(methylphenylsiloxane) filled with magnesium oxide, alumina and quartz sand, the synthesis of cordierite (2MgO•2Al2O3•5SiO2), mullite (3Al2O3•2SiO2) or magnesium aluminate spinel (MgO•Al2O3) is possible. The basic composition of the protective coating, which can be recommended for the protection of cordierite-mullite refractory, is proposed.

Fabrication of High Porosity Mullite Foams and their Thermal Properties

Already, we developed a high porosity alumina foam. However, alumina has high thermal conductivity about 36W/mK at room temperature, and it need to achieve to high porosity to decrease thermal conductivity to for application of refractory bricks. Therefore, high porosity mullite refractory brick is developed using GS (Gelation of Slurry) method that is already developed for production of high porosity metal foam. Appling this method to production of mullite foams, the ceramics foams from 93 to 97% porosity can be produced. Also, their thermal conductivities are proportional to densities and obey to Ashby-Glicksman model. Its thermal conductivity is about 0.07W/mK when density is 0.1 g/cm3. The high porosity mullite foams achieved enough thermal insulating properties for refractory brick.

Dynamic Transmission Performances of Alumina and Mullite Refractory Ceramics in Microwave High-Temperature Heating

This paper proposes an analytical approach to optimize the thickness of refractories for achieving maximum microwave power transmission in microwave heating based on the analysis of power transmission coefficient (PTC). The microwave PTCs of alumina (Al2O3) ceramics over the temperature range of 22–1,379°C at 2,450 MHz, mullite ceramics in the temperature range of 27–1,027°C at 2.45 GHz and 400–1,300°C at 915 MHz are studied. The results show that there are several transmission peaks in the PTC patterns. The transmission peak amplitude depends sensitively on the thickness of the refractory and the peak shifting towards a smaller thickness as the temperature of the refractory increases. We also show that high microwave transmission can only be achieved in a refractory with a small thickness corresponding to a slight transmission peak shift in the entire microwave heating (less than one eighth wavelength in the refractory).