How much does zirconia expand when it changes from tetragonal to monoclinic form?

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advanced structural ceramics Figure 1: Resistance to cracking in transformation-toughened zirconia. In a ceramic composed of tetragonal zirconia dispersed in a zirconia matrix, the stress field advancing ahead of a propagating crack transforms the small tetragonal particles to larger monoclinic particles. The larger particles exert a crack-closing force in the process zone behind the crack tip, effectively resisting propagation of the crack.

When pure zirconia cools below 1,150° C (2,100° F), it undergoes a volume expansion of approximately 3 percent as it transforms from a tetragonal crystal structure to a monoclinic form.1

This phase transformation is the basis for transformation toughening, a process used to enhance the fracture toughness of advanced structural ceramics. By dispersing fine tetragonal particles within a matrix, the resulting volume increase during the stress-induced transformation to the monoclinic phase exerts a closing force on cracks, effectively resisting their propagation.1