Theoretically dense and nanostructured ceramics by pressureless sintering of nanosized Y-TZP powders

Nanosized yttria-doped tetragonal polycrystalline zirconia (Y-TZP) powder was prepared by the coprecipitation method using isopropanol solutions of organic and inorganic precursors. A isopropanol-washing step led to a powder mainly constituted by very soft agglomerates with 6 nm crystallite size. Such a weakly agglomerated powder compacted uniformly (average diameter pore size = 6 nm) with a homogeneous shrinkage to full density. The small particle size of the Y-TZP powder, the small pores in the green compacts, and its homogeneous pore size distribution led to theoretically dense and nanostructured (< 100 nm) Y-TZP bodies by pressureless sintering at 1000°C for 80–100 h or at 1070°C for 2 h, in spite of the relative low green density (~43% theoretical). Comparatively, a commercial powder consisting of spherical weak agglomerates resulted in a fully densified ceramic but at higher sintering temperature (> 1200°C) and with a grain size higher than 0,25 mm.