Toughening function of glass fiber cloth refractory fiber (thermal shock resistance):
(As an additive, refractory fiber can improve the performance of conventional refractory materials. In refractory materials and high-density ceramic materials, adding refractory fiber improves the toughness of the matrix material, and can also be said to improve the resistance of aluminum silicate refractory materials. Thermal shock resistance. The introduction of a certain amount of short refractory fibers with a suitable length-to-diameter ratio can form a large number of microcracks in the refractory matrix, and the toughening of microcracks is one of the main mechanisms for refractory fibers to enhance the thermal shock resistance of refractory materials.
At the very beginning, fiber-toughened ceramic materials were used at home and abroad, mainly based on SiC and Si, N, which are relatively expensive. On the fiber, these fibers are easy to oxidize at high temperature, and the introduction of alumina refractory fiber solves the high temperature oxidation.
The refractory fiber reinforced ceramic matrix composite material is a new material with high strength, high thermal shock resistance, high oxidation resistance, high temperature resistance and wear resistance. In order to achieve the purpose of refractory fiber reinforcement, the refractory fiber and the matrix material must meet two conditions: first, the elastic coefficient of the fiber must be higher than the elastic modulus of the ceramic matrix; second, the fiber and the matrix must be compatible. Due to the limitations of these two basic conditions, only refractory fibers are compatible with ceramic-based refractory materials. Table 2-7 is the effect of the amount of refractory fiber added on the strength and thermal shock resistance of the refractory material, and Table 2-8 is the effect of the amount of refractory fiber added on the thermal conductivity and bulk density of the refractory material.
It can be seen from Table 2-7 that as the amount of fiber added increases, the strength increases slightly, but when the amount of fiber added reaches 12%, the strength shows a downward trend, and the residual strength retention rate shows an upward trend. The addition of refractory fiber has a significant impact on thermal shock resistance, but the introduction of more fibers will affect the combination of aggregate particles in the refractory material and the base material, so the amount of refractory fiber added is controlled at about 8%. To achieve a better strengthening and toughening effect.
It can be seen from Table 2-8 that as the amount of refractory fiber added increases, the bulk density of refractory products decreases, and the thermal conductivity decreases more significantly. When the amount of refractory fiber added is 12%, the bulk density of the product is reduced by 8%, but the thermal conductivity is reduced by 61.7%. This shows that it is also an effective method to improve the thermal insulation of the material and reduce the thermal conductivity by adding refractory fibers.
Two groups of samples with refractory fiber addition amount of 0% and 8% were selected, and the thermal shock temperature difference AT was 200C, 400, 600, 800 and 100C respectively. The sample is a small square with a size of 30mm x 30mm x 5mm, and the formation and propagation of cracks are observed with an optical microscope.
It can be seen from Figure 2-13 that when oT = 400C, the strength of the sample without refractory fiber drops more, and then as the temperature difference increases, the strength shows a rapid decline trend. When 4T = 10, the strength is only About 3MPa, it can be determined that the critical temperature of the sample is A.40. The strength of the sample added with 8% refractory fiber is gradually decreasing, and there is no sudden drop in strength. It can be concluded that the critical temperature difference of the sample is AT.=600C.