Commercially, 3 mol% Y 2 O 3 -stabilized tetragonal zirconia (70-90 nm) compacts were fabricated using a conventional and a nonconventional sintering technique; microwave heating in a resonant mono-mode cavity at 2.45 GHz, at temperatures in the 1100-1400°C range. A considerable difference in the densification behavior between conventional (CS) and microwave (MW) sintered materials was observed. The MW materials attain a full density of 99.9% of the theoretical density (t.d.) at 1400°C/10 min, whereas the CS reach only 98.0% t.d. at the same temperature and 1 h of dwelling time. Therefore, the MW materials exhibit superior Vickers hardness values (16.0 GPa) when compared with CS (13.4 GPa).*a.borrell@cinn.es

The aim of this work is to study the application of microwave sintering to consolidate yttria-stabilized zirconia polycrystalline (Y-TZP) ceramics commonly applied in dentistry, so as to obtain highly dense materials and fine microstructure with shorter sintering cycles. Three Y-TZP materials are considered: two commercially available for dental applications and one laboratory studied powder. Microwave sintering was carried out at 1200 and 1300 ºC for 10 min and conventional sintering at 1300 and 1400 ºC for 2 h. Relative density, Vickers hardness and fracture toughness values for sintered samples were determined. Microwave sintering results, generally, in improved mechanical properties of the materials in terms of hardness and fracture toughness compared to conventional sintering and, in some cases, at lower sintering temperatures.A finer grain microstructure (final grain size < 250 nm) was obtained with microwave sintering for both commercial materials. Fracture toughness values differ significantly between sintering techniques and chosen parameters. These results suggest that 2 microwave heating can be employed to sinter Y-TZP commercial ceramics for dental applications obtaining improving the mechanical properties of the materials with a very important time and energy consumption reduction.

Microwave sintering has emerged in recent years as a novel method for sintering a variety of materials that have shown significant advantages against conventional sintering procedures. This work involved an investigation of microwave hybrid fast firing of alumina-zirconia nanocomposites using commercial alumina powder and monoclinic nanometric zirconia. The suspensions were prepared separately in order to obtain 5, 10 and 15 vol.% of ZrO 2 in the alumina matrix. The samples were sintered in a 2 monomode microwave furnace at 2.45 GHz in air at different temperatures in the range 1200-1400 ºC with 10 min of dwelling time and 200 ºC/min of heating rate. The effect of sintering temperature in densification, mechanical properties and microstructure behaviour of the composites was investigated.Higher density, hardness and Young's modulus, excellent fracture toughness properties and homogeneous microstructure were achieved by microwave sintering in comparison to conventional heating. Microstructure analysis showed that the alumina grains had not grown significantly, indicating that the zirconia particles provided a hindering effect on the grain growth of alumina.