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Refractory materials, including complex refractories and rare earth corundum, can significantly enhance the thermal shock resistance of corundum-based ceramics. Thermal shock resistance is typically evaluated through parameters such as hot end area loss, residual flexural strength, or strength retention after a specific thermal cycle—such as 950°C followed by rapid cooling with water or air. This method is particularly suitable for materials subjected to bending loads.
To improve thermal shock resistance, refractory materials should aim to increase their workability and reduce the coefficient of thermal expansion (α). A higher E/α ratio is also beneficial, while maintaining moderate mechanical strength is essential. When the microstructure consists of fine grains, minimal grain boundary defects, small and uniformly distributed pores, the material exhibits better thermal shock resistance. For example, M-Si can promote a fine-grained structure in corundum, but it may leave pores and defects at the grain boundaries, which can negatively impact thermal shock performance. However, adding elements like Yao Chou or M4 can effectively reduce these defects, thereby enhancing the material’s resistance to thermal shock. Products made from A12 field plates also demonstrate excellent thermal shock resistance due to their favorable microstructure.
Tabular alumina, with its sheet-like structure, acts as a reinforcing skeleton in refractories and ceramics. This structure helps distribute stress evenly, reducing damage caused by rapid heating or cooling, thus significantly improving thermal shock resistance. Additionally, tabular alumina offers high thermal conductivity, good thermal stability, and strong erosion resistance, making it an ideal refractory material. However, its production process tends to be costly.
From the perspective of thermal expansion, when two-phase materials have a certain difference in thermal expansion coefficients, micro-cracks formed near the phase boundaries during firing can help improve thermal shock resistance without compromising mechanical strength. However, if the thermal expansion differences are too large, destructive cracks may form, leading to a decrease in mechanical properties.
Professor Shen Jiyao proposed that multiphase materials composed of two or more phases with controlled thermal expansion differences and appropriate proportions often exhibit superior thermal shock resistance compared to single-phase materials. Multiphase modification is therefore an effective strategy for enhancing refractory performance. In particular, using plate-like alumina as a matrix improves both the bending strength and thermal shock resistance of refractory products, contributing to better overall quality.
The addition of rare earth oxides promotes the sintering of corundum, resulting in highly dense materials with uniform microstructures and excellent thermal shock resistance. Transparent alumina tubes, thermocouple protective sheaths, and compounds doped with meta-magnesium or ytterbium also show outstanding thermal shock performance. These examples highlight the various methods available to improve the thermal shock resistance of corundum materials.
In this study, both sintering promotion and thermal shock resistance improvement were considered. The powder was fully processed and pressed on a Y71-LOA hydraulic press. Flat samples of 50x10 mm were molded under 80 MPa pressure to measure bulk density, while 2.5x5x25 mm bars were used for flexural strength and thermal shock tests. Dried samples were placed in a 63-D thermostatic oven at 90–105°C for about 4 hours. Finally, all samples were fired in a silicon-platinum rod high-temperature box furnace. Flexural strength was tested using a three-point bending method with a SJ-AZA three-axis shear instrument, YJ-16 static resistance strain meter, and a desktop automatic balance recorder. The sample dimensions were 2.5x5x25 mm.