Growth and coarsening of pure and doped ZrO2: A study of microstructure by small-angle neutron scattering

When precipitated zirconium hydroxide is heated above 3000C, an amorphous powder is formed which slowly crystallizes to tetragonal ZrO2. A high density of very small crystallites forms, which can be detected by small-angle scattering when they exceed approx. =2 nm in diameter. The growth and coarsening of these crystallites was studied in pure and MgO-doped ZrO2 from 3000 to 8000C. The small-angle neutron scattering (SANS) pattern is dominated by a strong interparticle interference peak which sharpens as the coarsening proceeds. The data can be simulated by a hard-sphere progressive potential model in which the particle size and spatial distribution are refined independently. The kinetics of precipitation growth and scattering intensity confirm a pure Ostwald ripening process. With a t1/sup/4 growth law corresponding to grain-boundary diffusion. The activation energy for coarsening calculated from the temperature dependence of the reaction is calculated to be 59 kJ/sup.mol-1/ for pure ZrO2 and 114 kJ/sup.mol-1/ for 3% MgO-doped ZrO2 over this temperature range, where the particle diameters range from 4 to 20 nm