thermal-shock-resistant design
If thermal shock is the disease, thermal-shock-resistant design is the cure: the deliberate choice of material and shape so a ceramic can weather sudden temperature changes without cracking. The recipe falls straight out of the R and R' parameters. To make R large you want high strength and low expansion and low stiffness; to make R' large you add high thermal conductivity. In plain words: pick a ceramic that expands little, conducts heat well, is strong, and is not too rigid — and if you cannot avoid cracks entirely, arrange for them to stop.
There are two philosophies, and good design knows which it needs. The first is crack avoidance: make the body strong and defect-free so no crack ever starts below the service shock. Here you reach for low-expansion materials (fused silica, cordierite, lithium-aluminosilicate glass-ceramics, aluminium titanate) or high-conductivity ones (silicon carbide, silicon nitride), and you keep the microstructure clean and flaw-free. The second is damage tolerance: accept that cracks exist and design so a shock only nibbles at them. Here you deliberately introduce porosity or microcracking to lower the modulus and expansion and to blunt and arrest running cracks — which is why a crumbly firebrick outlasts a pristine dense oxide through hundreds of furnace cycles even though it is far weaker. The two philosophies pull in opposite directions: one wants strong and dense, the other tough and porous.
Design is not only material choice; it is also geometry and operation. Avoid sharp corners and thick sections that build steep gradients, do not rigidly clamp a part that must expand, match the expansion of any coating or seal to its substrate, and heat and cool gradually whenever the schedule allows. The payoffs are everywhere: borosilicate and glass-ceramic cookware that goes from freezer to oven, cordierite honeycombs that survive a catalytic converter's thermal cycling, silicon nitride turbocharger rotors and diesel glow-plug tips, and refractory brick engineered porous on purpose so it shrugs off the daily shock of a steel furnace.
A cordierite catalytic-converter substrate is a masterclass in the approach: its near-zero expansion coefficient keeps thermal stress tiny, its thin honeycomb walls minimise gradients, and its slightly microcracked, low-modulus structure blunts any crack — together letting it survive thousands of cold-start-to-full-throttle cycles.
Low expansion, thin walls, and a crack-blunting microstructure combine to make cordierite a benchmark thermal-shock-resistant ceramic.
The two design routes conflict: maximising crack-initiation resistance calls for a strong, dense, flaw-free body, while maximising damage tolerance calls for a porous, microcracked, low-modulus one. You cannot have both at once, so decide up front whether your part must never crack or must survive with cracks.