Technical ceramics have high mechanical strength, hardness, wear resistance, heat resistance, and low density. In terms of conductivity, it is an excellent electrical and thermal insulator material.
After a thermal shock, which is rapid heating that causes the ceramic to expand, the ceramic can handle sudden temperature changes without cracking, breaking, or losing its mechanical strength.
Thermal shock, also known as "thermal collapse," is the disintegration of any solid substance caused by a sudden temperature change. The temperature change may be negative or positive, but it must be significant in either case.
Mechanical stresses form between a material's exterior (shell) and interior (core) as it heats or cools faster on the outside than on the inside.
The material is irreparably damaged when the temperature difference exceeds a certain threshold. The following factors have an impact on this critical temperature value:
Changing one or more of these can often improve performance, but as with all ceramic applications, thermal shock is only one part of the equation, and any changes must be thought of in the context of all performance requirements.
When designing any ceramic product, it is critical to consider the overall requirement and frequently find the best workable compromise.
Thermal shock is frequently the primary cause of failure in high-temperature applications. It is made up of three components: thermal expansion, thermal conductivity, and strength. Rapid temperature changes, both up and down, cause temperature differentials within the part, similar to a crack caused by rubbing an ice cube against a hot glass. Because of varying expansion and contraction, movement causes cracking and failure.
There are no simple solutions to the problem of thermal shock, but the following suggestions may be useful:
Select a material grade that has some inherent thermal shock characteristics but meets the requirements of the application. Silicon carbides are outstanding. Alumina-based products are less desirable, but they can be improved with proper design. Porous products are generally better than impervious ones because they can withstand greater temperature changes.
Products with thin walls outperform those with thick walls. Also, avoid large thickness transitions throughout the part. Sectional parts may be preferable because they have less mass and a pre-cracked design that reduces stress.
Avoid using sharp corners, as these are prime locations for cracks to form. Avoid putting tension on the ceramic. Parts can be designed to be pre-stressed to help alleviate this problem. Examine the application process to see if it is possible to provide a more gradual temperature change, such as by preheating the ceramic or slowing the rate of temperature change.
