The synthesis of mullite
Release time:
2023-08-25
The synthesis method of mullite can be divided into sintering method and electric melting tube fitting method. Sintering method according to the raw material production method and dry and dry method, dry processing technology is the seasoning together with cement powder, after pressing ball or compact fired by cement rotary kiln or tunnel kiln; The dry processing technology is to put the mixed material into water and grind it into slurry, and then dry it into filter cake by filter press, and squeeze mud into mud section or mud blank by vacuum pump and then fire.
The fusion tube method is to add the mutual matching material to the medium frequency furnace, melt in the high temperature weather generated by the electric arc, refrigerate crystallization, and choose natural raw materials seasoning (such as bauxite, etc.), without grinding immediately crushed small pieces of raw materials to <1.5mm particles can be mixed with other powdered raw materials in the mixing machine evenly.
Sintered mullite synthesis is generally carried out at 1650 ~ 1700℃. The specific processing elements of synthesis of mullite by sintering method are purity of raw material, mesh number of raw material and forging temperature. The key to the synthesis of mullite by sintering method is the solid-phase reaction between Al2O3 and SiO2, so the particle size distribution of the raw material is improved, which may speed up the in-phase reaction process.
In particular, particles <8μm have a very large effect on the establishment and sintering of synthetic mullite. It can be seen that sufficient mixing and grinding of raw materials is the main processing technology to promote the solid phase reaction of synthetic mullite. Mullite generally forms gradually at 1200 ° C and stops at 1650 ° C. When the temperature exceeds 1700℃, the crystal growth and development are good. It can be seen that the ignition temperature immediately harms the growth and development of mullite crystals.
Therefore, heating to a certain firing temperature and increasing a certain holding time are essential conditions for the synthesis of mullite. The purity of the raw materials commonly used in the synthesis of mullite is very strict, and a small residue composition can reduce the composition of mullite. In industrial production, it is difficult to avoid to bring a variety of residues, the book is Fe2O3, TiO2, CaO, MgO, Na2O, K2O, in which the harm is Na2O, K2O, they inhibit the production of mullite, and cause a lot of silicon-rich laminated glass phase caused by reducing the composition of mullite.
Fe2O3 slows down the mullite fossilization process and increases the total number of laminated glass phases. When there is a small amount of TiO2, a part of Ti positive ions enter the mullite properties to produce ionic crystals, promoting the establishment of mullite and the growth and development of crystals. When the TiO2 composition is too high, it still acts as a solution.
The mullite is prepared by melting the mutual compound in the medium frequency furnace, and the mullite is prepared by refrigeration crystallization from the melting. The crystallization process is similar to the crystallization process in the phase diagram of the Al2O3-SiO2 system software. When the Al2O3 of the mutual compound is higher than 71.8% of the basic theoretical group in mullite, the mullite ion crystal with dissolved Al2O3 of excess capacity, that is, β-mullite, will occur only when the Al2O3>80%.
The mineral phase composition of mullite in fused pipe fittings is generally mullite crystal and laminated glass phase. Compared with sintered mullite, fused pipe mullite crystal growth and development is sound, large crystals, fewer shortcomings, crystal specifications are hundreds of times that of sintered mullite, so sustained high temperature physical properties and corrosion resistance are relatively better.
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