When the clay refractory is in contact with molten glass at high temperature, the surface of the brick body is initially infiltrated by molten glass. Thereafter, due to the action of the capillary, the molten glass is sucked into the pores of the brick, and the alkali-rich ions in the melt will gradually diffuse into the gaps of the clinker product phase around the pores, and the metasomatism reaction occurs. Glass liquid first
Dissolve the free SiO2 in the refractory material, and the mullite is dissolved at a lower speed, so it gathers at the interface between the molten glass and the refractory material. After that, the small crystalline mullite is dissolved, and recrystallized (secondary) mullite is produced near the pores or at the interface in contact with the glass liquid. The clinker may also be transformed into β-Al2O. Because the explanation is not deep, most of these crystal grain sizes are very fine. In addition, the metasomatization reaction also forms a part of the glass phase that has a different composition from the original glass liquid. This is because the clinker is partially dissolved, and SiO2 and Al2O2 components are added to the melt. These melts will diffuse into the rest of the glass liquid. With the development of the metasomatic reaction, the clinker particles will gradually disintegrate and become residual aggregates, and there may be grown up mullite and β-Al2O3 around them, and β-Al2O crystals will gather in the interface layer. Nepheline and glass phases may also appear. At this stage, Na2O and K2O have penetrated into the clinker agglomerates. It reacts with mullite in clinker as follows:
3Al2O3?2SiO2+Na2O=NaO?Al2O3?2SiO2+2Al2O3
Mullite nepheline
When mullite coexists with R2O, it will decompose at a lower temperature. The more R2O, the lower the temperature at which mullite decomposes into corundum and nepheline liquid phase. The alkaline components from the metasomatic interface into the brick body gradually diffuse inward, so the alkaline components in the interface layer are high, and the BAl2O3 crystals aggregate more.
With the further development of metasomatism, the clinker particles may be transformed into fragmented layers, and even all of them will be transformed into secondary or new mineral facies. They mainly include secondary mullite and BAl2O derived from decomposition and conversion and Xia generated by metasomatic reaction. Stone, striline nepheline, leucite, orthoclase, albite, etc. After further erosion, they will melt into the molten glass and become high-aluminum streaks or bumps.
This erosion is most intense at the liquid surface of the glass, where not only the temperature is high, but also at the junction of the gas, liquid and solid phases, and the surface will be affected by the lye and nitrate in the batch. The nitrate water reacts with clay bricks to produce SiS. When this substance decomposes, gases are generated to foam the metamorphic layer of the bricks, thereby accelerating erosion. The volatiles of alkali metal oxides can react with clay bricks at 1000~1100℃, that is, R2O reacts with mullite in clay bricks to form corundum and nepheline glass phase. The latter continues to be affected by R2O to form a feldspar glass phase. If the main component of R2O is K2O, a strong protective layer of potash and BAl2O2 in the high-viscosity zone can be formed on the surface of the clay brick. However, if the brick contains less SiO2, the glassy glaze layer will remain after the reaction with R2O.
After the clay bricks in the regenerator are eroded by the batch dust, a layer of glaze is formed. In addition to the glass phase, this layer of glaze also has complex twin crystals of nepheline, leucite, feldspar and mullite. This glaze layer will be lost at higher temperatures. Residues solidify at the lower temperature of the checker bricks and easily block the checker holes, which will greatly reduce the heat storage effect of the checker bricks in the regenerator. It is usually difficult to use clay checker bricks for more than 30 months.
