G. Pacheco et Jj. Fripiat, Physical chemistry of the thermal transformation of mesoporous and microporous zirconia, J PHYS CH B, 104(50), 2000, pp. 11906-11911
In fine-grained zirconia, the order of stability of the three polymorphs is
exactly the reverse of that observed in a coarse-grained sample. Starting
from a disorder amorphous material, the crystallization into the cubic form
occurs, in general, below 500 degreesC. It is followed, or accompanied, by
the formation of tetragonal ZrO2 and, finally, by the crystallization into
monoclinic zirconia above 700 degreesC. This sequence is observed in mesop
orous and microporous zirconia. It has been suggested that this anomalous b
ehavior is due to a high surface energy of the monoclinic phase or to strai
ns present in the small particles. It is shown here that the surface effect
explains satisfactorily and semiquantitatively the observations. This does
not rule out other factors.