R. Gopalan et al., THERMAL-STABILITY IMPROVEMENT ON PORE AND PHASE-STRUCTURE OF SOL-GEL DERIVED ZIRCONIA, Journal of Materials Science, 30(12), 1995, pp. 3075-3081
Thermal stability improvement of mesoporous zirconia is important for
its applications as catalyst supports or membrane layers at high tempe
ratures. Yttria-coated zirconia is synthesized by doping a small amoun
t of yttrium nitrate solution in zirconia sol. The sol-gel derived und
oped and 2 and 3 mol% yttria-doped zirconia samples after calcination
at 450 degrees C are in the metastable phase. Undoped zirconia starts
to transform to thermodynamically stable monoclinic phase at 600 degre
es C. The yttria-doped zirconia samples remain in the metastable phase
after heat treatment in air at 900 degrees C for 30 h. Doping yttria
also retards the sintering and grain-growth rates of the sol-gel deriv
ed zirconia. Doping with 2 mol% yttria gives the most effective result
s with respect to retarding the surface area loss of zirconia at high
temperature. Yttria with a loading up to 2 mol% is possibly present on
the grain surface of zirconia. The improvement of the thermal stabili
ty of zirconia by coating yttria is explained in terms of the effects
of dopant on the mobility and concentration of the surface defects.