The role of the synthesis route to obtain densified TiO2-doped alumina ceramics

Alumina specimens doped with 1 wt.% of titanium oxide were successfully prepared by three different synthesis routes: Pechini method, coprecipitation and sol–gel processes. This paper describes the phase sequence in each synthesis process and its effect on the final particle size and shape, as well as, on the microstructure of the calcined powders and the sintering behaviour. The intermediate phases to obtain α-alumina were κ-Al2O3, θ-Al2O3 and γ-Al2O3for the Pechini, coprecipitation and sol–gel processes, respectively, as could be detected by FT-IR and XRD. Secondly, the calcined powders were isopressed and sintered at 1625 °C for 4 h. Density measurements, and microstructure were investigated by Archimedes method and TEM/SEM, respectively. The sintering behaviour of the materials is discussed on the basis of the characteristic of the metastable phases obtained by each route. Coprecipitation yielded rounded particles with the smallest size. Sol–gel process produced larger grains with vermicular shapes and Pechini method led to hexagonal corundum crystals.