02The effect of silicon carbide addition amount on sample performance
Based on sample M3, add silicon carbide fine powder with mass fractions of 10%, 12%, 14% and 16% respectively, and adjust the M80 homogenized alumina content accordingly to prepare samples C1 and C2 (M3). , C3, C4. Figure 1 shows the effect of SiC addition on the physical properties of the sample after calcination at 1490°C for 3 hours. It can be seen from Figure 1 that as the addition amount of silicon carbide increases, the apparent porosity of the sample decreases. This is caused by the oxidation of silicon carbide at high temperatures to form a glass phase, which forms a glaze layer on the surface of the product and blocks the pores. The load softening temperature also tends to decrease. This is due to the oxidation of silicon carbide to form silicon dioxide, which increases the amount of liquid phase in the product at high temperatures. Taken together, the performance of sample C2 with 12% (w) silicon carbide is better.
03The effect of the addition amount of andalusite on the performance of the sample
Based on sample C2, add andalusite with mass fractions of 4%, 8%, 12%, and 16% and particle sizes of 2 to 1 and ≤0.088mm respectively, and adjust the M80 homogenized alumina content accordingly to prepare Samples G1, G2, G3, G4, F1, F2, F3, F4.
For samples with 2 to 1mm large-grained andalusite added, as the amount of andalusite increases, the linear change rate after burning increases, especially for samples G3 and G4 with 12% and 16% (w) additions. The line change rate after burning increases significantly; while the line change rate of the sample with ≤0.088mm andalusite fine powder added does not change much after burning. This may be because the primary mulliteization (3Al2O3·SiO2)→3Al2O3·2SiO2+SiO2) and the secondary mulliteization (3SiO2+2Al2O3→3Al2O3·2SiO2) of andalusite with particle size ≤0.088mm are larger before 1450℃. Part of it has been completed. Although mulliteization is still continuing at 1490°C, due to the effect of sintering, the volume increase effect of the sample becomes less obvious. The volume expansion of the sample is caused by the decomposition of andalusite and secondary mulliteization. The degree of mulliteization of andalusite is related to the calcination temperature and the particle size of andalusite. When ≤0.088mm andalusite fine powder is added, after firing at 1490°C, the sample is mainly sintered, and the volume shows shrinkage or little change. After the andalusite with a particle size of 2 to 1 mm is calcined at 1490°C, the decomposition is not very obvious. The secondary mulliteization reaction and the sintering reaction mainly occur in the sample, and the large particle size is not conducive to the sintering of the green body. Therefore, at 1490 At ℃, the sample will expand in volume.
It can be seen from the figure that when andalusite particles are added, the normal temperature compressive strength of the sample decreases as the amount of andalusite increases; when ≤0.088mm andalusite fine powder is added, the normal temperature compressive strength of the sample is within a certain range The internal structure increases as the amount of andalusite increases, but as the amount further increases, the volume expansion caused by the primary mulliteization and secondary mulliteization of a large amount of andalusite makes the internal structure of the sample loose, and the bonding between particles The force is reduced, resulting in a reduction in the normal temperature compressive strength. However, for the sample with andalusite fine powder added, mulliteization has been completed after burning at 1490°C. The sintering of the sample plays a leading role. A mullite reinforced structure is formed inside the material, and the compressive strength is not reduced, even within a certain range. There has been some improvement within.
As the addition amount of andalusite increases, the load softening temperature of the sample gradually increases first and then decreases. This may be due to the fact that within a certain range, the expansion of a small amount of andalusite during the mulliteization process in the sample causes the material to become more compact, and its load softening temperature increases as the addition amount increases; while when the addition amount of andalusite fine powder > At 12% (w), a stable mullite structure is formed at this time, and the excessive SiO2 glass phase in the sample cannot be completely transformed into secondary mullite, resulting in a decrease in the load softening temperature.
In view of the fact that the linear change rate, compressive strength and load softening temperature of the sample with a particle size of 2 to 1 mm andalusite added are not as good as those with a fine powder with a particle size of ≤0.088 mm, so only the addition of ≤0.088 mm was used when examining the thermal shock resistance. mm fine powder sample. Figure 5 shows the effect of the addition amount of andalusite fine powder on the thermal shock resistance of the sample after calcining at 1490°C for 3 hours. As the amount of andalusite fine powder added increases, the number of 1100°C water cooling cycles increases, and the thermal shock resistance gradually improves. This is because the sample with andalusite fine powder has been burned at a high temperature of 1490°C and the primary mulliteization and secondary mulliteization have been completed. A stable structure has been formed in the sample, and the excess SiO2 glass phase has played a role in the sample. The role of filling pores; at the same time, the thermal shock resistance may be improved due to the increase in high-temperature liquid viscosity of the silicate glass phase.
For refractory materials used in the transition zone of cement kilns, considering various performance requirements, it is appropriate to add 10% to 12% (w) andalusite fine powder.
03Conclusion
(1) Using M60 and M70 alumina-based sintered mullite as aggregate and 80 homogenized material and 85 homogenized material as fine powder can solve the problem of unstable high-temperature performance of products caused by natural alumina as raw material.
(2) A sample using M70 alumina-based sintered mullite as aggregate, 80 homogenized material as fine powder, and a mass ratio of aggregate to fine powder of 5545 will form a well-developed mullite structure after being fired at high temperature. , while the silicon carbide and glass phases are evenly distributed around the boundary.
(3) Considering the comprehensive performance of the sample, it is appropriate to add 12% (w) silicon carbide fine powder and 10% to 12% (w) andalusite fine powder.