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How do large grains and pores help some refractory ceramics resist thermal shock?

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traditional ceramics Stages in the slip casting of a thin-walled whiteware container. Clay powder is mixed in water together with a dispersing agent, which keeps the clay particles suspended evenly throughout the clay-water slurry, or slip. The slip is poured into a plaster mold, where water is drawn out by capillary action and a cast is formed by the deposition of clay particles on the inner surfaces of the mold. The remaining slip is drained, and the cast is allowed to dry partially before the drain hole is plugged and the mold separated. The unfinished ware is given a final drying in an oven before it is fired into a finished product.

In refractory ceramics, the presence of large grains and pores serves as a structural mechanism to enhance resistance to thermal shock. When a ceramic object is rapidly cooled from a high temperature, the surface layers contract against the inner layers, creating tensile stress that typically leads to crack propagation.

While the inclusion of large grains (often on the scale of millimetres) and significant porosity reduces the overall load-bearing strength of the material, these features are effective at blunting cracks as they develop. By interrupting the path of a crack, these microstructural elements reduce the material's susceptibility to failure under thermal stress. However, it is important to note that this porous structure is generally undesirable in environments where the refractory must contact corrosive substances, as higher density is required to prevent degradation in those specific conditions.1