The magnitude of thermal stress in ceramic materials depends on the mechanical and thermal properties of the materials. It is also affected by factors such as the geometry of the components and the environmental medium. Therefore, thermal shock resistance, which is a sign of the ability of ceramic materials to resist temperature changes, must also be a comprehensive expression of its mechanical and thermal properties corresponding to various heating conditions. The thermal shock stability of alumina tubes is between 200 to 250 △T.℃.
The study of the thermal shock resistance of ceramic materials began in the 1950s. So far, various thermal shock resistance evaluation theories have been proposed, but they all have limitations and one-sidedness to varying degrees. Experiments have shown that with the changes in the sample size rm and the surface heat transfer coefficient h. From the changes in each curve, as the product of the sample size and the surface heat transfer coefficient increases, the thermal shock temperature difference that the material withstands for thermal stress damage decreases significantly at the beginning, and when it reaches a certain level, it tends to be a constant. Similarly, changes in material properties will also have a significant impact.
Studies have shown that the presence of a moderate amount of cracks will help Al2O3 ceramics improve their thermal shock damage resistance. For example, in non-dense Al2O3 ceramics with a porosity of 10% to 20%, the formation of thermal shock cracks is often inhibited by pores, because the presence of pores plays a role in passivating cracks and reducing stress concentration. On the contrary, dense Al2O3 ceramics are prone to bursting under thermal shock.
Engineering applications have increasingly stringent requirements for ceramic materials, and single-phase materials are increasingly difficult to meet their use requirements. Therefore, it is often necessary to combine materials to make up for their shortcomings and prepare dual-phase or multi-phase ceramic composite materials with better comprehensive performance. For example, the composite material of Al2O3 toughened with ZrO2 is one example.
Some studies have found that the thermal shock resistance of Al2O3 composite materials after adding SiC whiskers is significantly higher than that of pure Al2O3 materials. SiC whiskers significantly improve the thermal shock resistance of Al2O3 ceramics.
SiC whiskers can improve the thermal shock resistance of Al2O3, ZrO2, and Al2O3+ZrO2 ceramics. The reasons can be attributed to the following: SiC whiskers have higher thermal conductivity and lower thermal expansion coefficient, which is conducive to reducing the thermal stress of composite materials during thermal shock; in addition, whiskers can also play a significant role in strengthening and toughening through mechanisms such as pull-out, bridging and deflection of induced cracks. However, there is sometimes an optimal value for whisker content, and the more the better. Studies on Al2O3 polycrystalline ceramics show that as the grain size increases, the expansion behavior of thermal shock cracks in the material also changes from a discontinuous dynamic form to a continuous quasi-static form.
Edgetech Industries is a leading supplier of Al2O3 ceramics. With our expertise, we are committed to producing reliable, durable alumina ceramic products that meet the stringent requirements of the industry.