According to the experiment, it is not easy to obtain low creep high aluminum bricks with a creep rate of less than 0.8% with 1350e, 0.2MPa and 50h using natural high alumina bauxite clinker. However, certain additives must be added to improve the structure and material of the material. Microstructure to improve its high creep properties at high temperatures, the addition of andalusite gradually converts to mullite at 13501400e, a volume expansion of 3% 5%, and is relatively stable, the additive silicon powder is a high-silicon mineral, Molybdenum reacts with the corundum phase in the matrix at high temperatures, causing a volume expansion effect of about 10%, and the active alumina powder must be added.
Because andalusite is a typical type of aluminum silicate, its chemical formula is 3Al2O32SiO2. Its crystals keep the density and volume unchanged after calcination, and thus its internal porosity does not change. Its prismatic crystals are several millimeters in size. Each crystal grain is a single crystal or a fragment of crystal. Its mullitization process starts slowly and smoothly from 1200e. Since the linear expansion is small, it only has a small amount. The glass phase cannot occupy the free space of the mullite crystals and become free.
The silica-enriched glass, which is separated from the particles, can participate in the reaction of the alumina addition to form secondary mullite, and the secondary mullite acts as a ceramic bond between the primary mullite components. The role of the agent is such that when the andalusite microparticles are mixed with the finely pulverized alumina, the secondary mullite needle crystals develop due to the reaction between the glass phases formed by the regeneration of the andalusite mullite. . In this way, the properties of the andalusite, microsilica, and A-Al2O3 have the following characteristics: volume stability, high mechanical strength, excellent creep resistance, high thermal shock resistance, good CO resistance, low thermal conductivity , good chemical stability, very low porosity and good anti-shedding effect.
1 The creep rate is -1.26%, which is significantly higher than the 2 formula. This is due to the fact that the additive andalusite is partially converted to mullite during firing of the 1450e brick. Due to the low addition of andalusite, the microstructure structure of the product is not improved enough, and thus the high temperature creep resistance is improved. The effect is not great; the creep of 2 and 3 is low and the effect is obvious. The above reactions all cause the volume expansion effect and can compensate the compression under the action of external stress.
As the amount of andalusite is increased, the amount of mullite produced is large, a needle-like network structure is formed in the matrix, and the microstructure is optimized, so the creep performance is improved. Under the premise of constant sintering temperature and other process conditions, the apparent porosity, re-sintering line change rate, and post-fired line change rate of the product increase with the increase of the amount of andalusite, while the load softening temperature shows a curve change. The peak value was reached at 15%. The amount of andalusite added affects the creep performance.
The influence of the amount of andalusite added on the creep performance is mainly due to the high content of impurities in the raw materials and the presence of more glass phases at 1350e. The formulation of the matrix is ​​further optimized for the formulation 5, and the additive silicon powder is used. The mullite reaction occurs in corundum at a high temperature and generates a volume effect. The creep rate of the product studied by the above-mentioned process measures is -0.48%, and the effect is significant.
Based on the amount of fixed andalusite added, the formula increases the purity content of the raw material, which is significantly lower than the creep rate of the formula 1. The reason is to add high-purity synthetic mullite and corundum to reduce the matrix composition, 3, 4 formula added high-purity raw materials, increase the amount of additive B, with the increase in the amount of creep rate decreased. The reason is that there is one mullitization and two mullitization in the heating process of B, the volume expansion is 7% 8%, and the conversion rate is slower. With the increase of the amount of addition, the volume effect produced by mullitization is large, compensating the outside. The amount of stress compression, so the creep performance increases. However, due to the volume expansion effect and the addition of high-purity raw materials, the product is not easy to sinter, so it is necessary to add a sintering agent M. To promote sintering, improve the degree of compactness of the product, so the addition of the sintering agent M formula 4 creep better.
Effects of several factors on the performance of the product The effect of mud moisture on the performance of the product Due to the low water absorption of the raw materials used, the moisture content of the mud has a great influence on the apparent porosity of the product. The relationship between mud moisture and apparent porosity is shown. According to the knowledge, high or low moisture content will result in high porosity of the product, and the appropriate moisture content is 2.8% 3.0%.
Relationship between mud moisture and apparent porosity The effect of firing temperature on product performance Under the premise of constant addition of additives, the relationship between the physical and chemical properties of the product and the firing temperature can be seen from the knowledge, the rate of change after burning and The apparent porosity increases with the increase of the firing temperature; the highest softening temperature of the load and the resistance to the normal temperature at 1450e.
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