A nanometric silicon oxycarbonitride powder was synthesised by CO_2 laser pyrolysis from a mixture of an aerosol of a liquid precursor (hexamethyldisilazane, HMDS), a gaseous precursor (silane, SiH_4) and ammonia. The amorphous nanopowder and the sintering aids (6 wt yttria and 3 wt alumina) were mixed together in ethanol and de-agglomerated by milling with Si_3N_4 balls. The mixture was then dried and sintered to nearly full density by hot-pressing. The nature and amount of the crystalline phases in the as-sintered materials appeared to be very sensitive to the drying stage. When drying was performed in a confined atmosphere, a noticeable amount of Si_2N_2O was detected in addition to β-Si_3N_4, whereas the crystalline phases were α- and β-Si_3N_4, when the slip was dried under vacuum. The creep behaviour of the two grades was assessed under compressive loading in air. The creep deformation of the Si_2N_2O containing material was about twice that of the other material under the same test conditions.
展开▼
