The synthesis method of mullite can be divided into sintering method and electrofusion pipe fitting method. The sintering method is divided into dry method and dry method according to the method of raw material preparation. The dry processing method is to grind the seasoning together with cement, and then use the cement rotary kiln or tunnel kiln after briquetting or compacting; dry processing. The process is to grind the mixed materials into slurry with water, and then de-dry it into a filter cake by a filter press.
The method of electrofusion pipe fittings is to add mutual batching materials into the intermediate frequency furnace, melt in the high temperature weather generated by the electric isolation, and refrigerate and crystallize. When using pure natural raw materials (such as bauxite, etc.) The small pieces of raw materials can be crushed to <1.5mm particles, and then mixed with other powdered raw materials in a mixer evenly.
The mullite synthesized by sintering is generally carried out at 1650-1700 °C. The specific processing elements of mullite synthesis by sintering method are the purity of raw materials, the mesh number of raw materials and the calcination temperature. The key to the synthesis of mullite by sintering is to use the solid-phase reaction between Al2O3 and SiO2, thus improving the particle size distribution of the raw materials, which may speed up the process of in-phase reaction.
Especially the particles <8μm have great effect on the establishment and sintering of synthetic mullite. It can be seen that the raw materials are sufficiently mixed and refined, which is the main processing technology to promote the solid phase reflection of synthetic mullite. Mullite generally forms gradually at 1200°C and stops at 1650°C. At this time, it is microscopic, and when the temperature exceeds 1700 ° C, the crystal growth and development are good. It can be seen that the ignition temperature immediately harms the formation of mullite and the growth and development of crystals.
Therefore, heating to a certain firing temperature and increasing a certain holding time are necessary conditions for synthesizing mullite. The purity requirements of the commonly used raw materials for synthesizing mullite are very strict, and a small amount of residue will reduce the composition of mullite. In industrial production, it is inevitable to bring various residues. The book contains Fe2O3, TiO2, CaO, MgO, Na2O, K2O, among which Na2O and K2O harm people, which inhibit the production of mullite, And lead to the formation of a lot of silicon-rich laminated glass phase, reducing the mullite composition.
Fe2O3 slows down the mulliteization process and increases the total number of laminated glass phases. When a small amount of TiO2 exists, a part of Ti positive ions enter into the mullite quality to generate ionic crystals, which promotes the establishment of mullite and the growth and development of crystals. When the TiO2 composition is too high, it still functions as a solution.
Electric melting pipe fittings mullite is produced by melting the mutual batch materials in an intermediate frequency furnace, and the mullite is obtained by cooling and crystallization from the melting. The whole crystallization process is similar to the crystallization process of the Al2O3-SiO2 system software phase diagram. When the Al2O3 of the mutual material is higher than 71.8% of the basic theoretical group in the mullite, the mullite ion crystal with the excess capacity Al2O3 dissolved, that is, β-mullite, occurs only when Al2O3>80%. Steel Jade Phase.
The mineral phase composition of mullite for electrofusion pipe fittings is generally mullite crystal and laminated glass phase. Compared with sintered mullite, the mullite crystal growth of electrofusion pipe fittings is sound, the crystal is large, and the defects are few. The crystal size is hundreds of times that of sintered mullite, so the physical properties and corrosion resistance of continuous high temperature are relatively better.
