Synthesis Of Mullite
The synthesis methods of mullite can be divided into sintering method and electric melting method. Sintering method can be divided into dry method and wet method according to the way of raw material preparation. The dry method is to grind the ingredients together and then burn them by rotary...
The synthesis methods of mullite can be divided into sintering method and electric melting method. Sintering method can be divided into dry method and wet method according to the way of raw material preparation. The dry method is to grind the ingredients together and then burn them by rotary kiln or tunnel kiln after pressing ball or compact. The wet process is to grind the compound material into slurry with water, then press and filter to dehydrate into mud cake, and vacuum squeeze mud into mud section or mud blank and then burn.
The electric melting method is to add the compound material to the arc furnace, melt in the high temperature formed by the arc, cooling crystallization, the use of natural raw materials (such as bauxite, etc.), can be crushed directly to <1.5mm particles without grinding, and then mixed with other powdered raw materials in the mixer evenly.
Synthesis of mullite by sintering is generally carried out at 1650 ~ 1700℃. The main factors affecting the synthesis of mullite by sintering are purity of raw material, fineness of raw material and calcination temperature. The synthesis of lenite by sintering method mainly depends on the solid phase reaction between Al2O3 and SiO2, so improving the dispersion of the raw material will accelerate the process of the same phase reaction. In particular, the particles <8μm have a great effect on the formation and sintering of synthetic mullite. It can be seen that the full mixing and fine grinding of raw materials is an important process condition to promote the solid phase of the synthesis of mullite. Mullite generally begins to form at 1200 ° C and ends at 1650 ° C. At this time, it is micro-grained, and the crystallization develops well when the temperature exceeds 1700℃. It can be seen that the combustion temperature directly affects the formation and crystal development of mullite. Therefore, heating to a certain firing temperature and extending a certain holding time are necessary conditions for the synthesis of mullite. The purity of the raw materials used to synthesize mullite is very strict, and a small amount of impurities will reduce the content of mullite.
In industrial production, it is inevitable to bring a variety of impurities, such as Fe2O3, TiO2, CaO, MgO, Na2O, K2O, among which the most harmful are Na2O and K2O, which inhibit the formation of mullite, and lead to the production of a large number of silica-rich glass phases, reducing the mullite content. Fe2O3 slows the process of mullite fossilization and increases the number of glass phases. When a small amount of TiO2 exists, part of Ti ions enter the mullite character to form a solid solution, promoting the formation of mullite and crystal development and growth, when the TiO2 content is too high, it still plays the role of flux. Electromelting mullite is prepared by melting the compound in an arc furnace and cooling mullite from the melt. The crystallization process is similar to that of the phase diagram of the Al2O3-SiO2 system.
When the Al2O3 of the compound is higher than 71.8% of the theoretical group in mullite, a mullite solid solution with excess Al2O3 is formed, that is, β-mullite, and only when the Al2O3>80% will appear corundum phase. The mineral phase composition of fused mullite is generally mullite crystal and glass phase. Compared with sintered mullite, fused mullite crystals are well developed, with large grains and fewer defects, and the crystal size is hundreds of times that of sintered mullite, so the high temperature mechanical properties and erosion resistance are relatively good.
Hot Tags: synthesis of mullite, China synthesis of mullite manufacturers, suppliers, refractory silicates, refractory for heaters, refractory for waste heat recovery systems, refractory leadates, refractory for barbecues, refractory perchlorates
You Might Also Like
Send Inquiry
