Zirconia polymorphs

Question 1

What are the crystal structures of zirconia?

Answer 1

~ room-temp symmetry of ZrO2 is monoclinic

~ transforms sluggishly to tetragonal at 1100-1200C

~ this then transforms to cubic at 2285C, which is the fluorite structure

Question 2

What happens during the monoclinic to tetragonal transformation?

Answer 2

~ has an associated 3-5% volume change (contraction): material is severely weakened by this transformation

Question 3

How is zirconia stabilized into the cubic (fluorite) structure?

Answer 3

~ done over a broad temp range via batch additions of CaO, MgO, or Y2O3