Magnesia-alumina spinel brick is a new type of refractory material produced by replacing magnesia-alumina spinel in magnesia-alumina brick. The chemical formula of magnesia-alumina spinel (MA) is MgO· Al2O3, in which MgO accounts for 28.2% and Al2O3 71.8%. When magnesia-alumina spinel brick is made of equiaxed minerals, N=1.715, hardness =8, density 3.55, melting point 2135℃, thermal shrinkage coefficient about 8.5x10-6k-1, the thermal shock resistance of refractory material can be greatly improved by adding magnesia-alumina spinel in magnesia. However, alumina can not improve the indirect refractory bonding degree, and can not fluctuate the C2S in the kiln skin. Therefore, the function of magnesia-alumina spinel brick is not as good as that of magnesia-alumina spinel brick. Therefore, the examination method of magnesia alumina spinel brick is to alleviate these defects and stop.
So far, four generations of magnesia-alumina spinel bricks have been developed. Among them, the first generation of goods have been eliminated: the second generation is used in the transition zone; the third generation, especially the fourth generation, is used in the cement kiln firing zone. The first generation of spinel brick is added alumina or high bauxite fine powder, made by sintering. Due to the composition of a small amount of in-situ magnesia alumina spinel at low temperature, the structure of the brick is lax. The second generation of products added decomposed spinel made of data, its volume density, apparent porosity, corrosion resistance and other functions have been greatly improved.
The third generation magnesia alumina spinel brick is made by combining the second and first generation technology. In brick making, one part of the spinel is predecomposed and the other part is in situ. In this way, the loosening effect that constitutes the magnesia-alumina spinel can be used to improve thermal shock resistance. The fourth generation of goods is made of fused spinel instead of sintered spinel refractories. Because the structure of fused magnesia alumina spinel is compact and the grain size is large, it is beneficial to improve the corrosion resistance of refractory materials and the leather of hanging kiln. Nevertheless, the hanging kiln skin and corrosion resistance of magnesia-aluminum materials are not as good as those of magnesia-chromium materials. Regarding magnesia-alumina spinel brick, such as improving its thermal shock resistance and reducing thermal conductivity, it is necessary to improve the amount of spinel. But such as improvement of corrosion resistance, hanging kiln skin, it is necessary to reduce the amount of spinel.
In order to understand this contradiction, it is necessary to increase the content of Al2O3 in the magnesia-alumina series data and add zirconia ZrO2 at the same time to prepare zirconium-containing magnesia-alumina spinel brick. Lanthanum zirconate La2O3·2ZrO2 will be formed when La2O3·2ZrO2 is added in the magnesia-alumina-zirconate refractory material of about 1%. With the addition of La2O3+ZrO2, the Mg-Al series data can obtain excellent thermal shock resistance and kiln skin hanging property. However, the price of ZrO2 and La2O3 is very high. Even if a large number of ZrO2 and La2O3 are added, the cost of goods will be added and the sales of goods will be affected.
Magnesium alumina spinel bricks also have weaknesses:
(1) poor hanging kiln skin.
(2) High thermal conductivity
(3) The spinel component in the brick is easy to react with the C3S or C3A in the cement clinker under the condition of overheating to generate C12A7 with low melting point, which leads to the burning flow of the kiln layer and forms the corrosion loss of the spinel mineral. These unfavorable factors limit the use of magnesia alumina spinel brick.
Two conditions are required for the application of magnesia-alumina spinel bricks in cement kiln firing zone:
(1) Cement kiln has the conditions to form a good kiln skin:
② carefully maintain the kiln skin.
Because C3S and C3A in cement clinker cannot coexist with magnesia-alumina spinel Ma, CaO and SiO2 in cement clinker and magnesia-alumina spinel brick will disperse into refractory material when they contact at low temperature. In the cement clinker, C3S will decompose and form C2S in small amounts in situ. In the refractory material, MA will be corroded, and the composition is close to the vitreous phase of calcium aluminum xanthite C2As. Thus, on the one hand, the kiln shell is easy to burn or collapse due to C2S pulmerization; on the other hand, the refractory data can not be ineffective maintenance of the kiln shell, so it will be damaged by deepening corrosion. Therefore, the key to the use of magnesia alumina spinel bricks is to quickly hang the kiln shell and maintain the kiln shell consistently.
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