How can the microstructure of a ceramic refractory improve thermal-shock resistance?

The microstructure of a ceramic refractory can be adjusted during processing to improve its resistance to thermal shock, which occurs when rapid cooling causes surface layers to contract against inner layers, leading to tensile stress and crack propagation.1

To mitigate this, manufacturers often engineer a coarse microstructure characterized by:

• Large filler grains: Unlike the fine, micrometre-scale grains found in whiteware, refractory grains are often on the scale of millimetres. These large grains help blunt advancing cracks, thereby reducing the material's susceptibility to failure.1
• Controlled porosity: Incorporating significant amounts of air spaces of varying sizes can also blunt cracks. While this porosity may reduce the overall load-bearing strength of the material, it is a common strategy for enhancing thermal-shock resistance.1

It is important to note that these microstructural features involve a trade-off. In environments where the refractory must contact corrosive substances, such as in glass-melting furnaces, high porosity is undesirable, necessitating a denser material structure.1