Homogeneous doping of ceramics by infiltration–gelation

Advanced ceramics require small amounts of cation dopants to improve the sintering process or achieve certain properties. Dopant precursors are often dissolved in initial processing liquids, which may adversely affect ceramic colloidal stability, and dopant transport during drying. This would lead to chemical and microstructural inhomogeniety in the eventual ceramics. Here we present a method that circumvents these problems using the example of Al3+-doped TiO2 ceramics. Homogeneous TiO2 compacts with 34% porosity are first prepared by colloidal casting and calcined at 700 °C. The obtained compacts are infiltrated with an aqueous solution of Al(NO3)3, citric acid and ethylene glycol. The solution composition is adjusted such that during drying, a gel forms that covers the internal pore surface. Subsequent decomposition of organics results in a homogeneous dopant distribution in the porous and then dense-sintered TiO2 compacts. This is verified with SEM-EDX, and laser ablation coupled ICP-MS on dense compacts sintered at 1100 °C.