Colloidal filtration of silicon nitride aqueous slips, part II: Slip casting and pressure casting performance

rn a previous part, the rheological behaviour of silicon nitride aqueous slips was optimized by dispersing with TMAH up to pH 11.5 using different mixing procedures and including different concentrations of sintering aids (Al2O3 and Y(2)O3). rn this part, the obtention of pressureless sintered silicon nitride bodies by colloidal filtration techniques is studied. The kinetics of the different compositions is studied for both slip casting and pressure casting. The pressure casting kinetics is up to 20 times faster than that of slip, casting, which allows the scale-up of the process for a low cost production, The obtained green density is slightly >58%th for slip casting and 57-55%th for pressure casting, depending on the applied pressure. This small difference does not influence sintered density. At 1750 degrees C/2 h, a final density around 96% th is obtained. The sintering conditions are studies considering the time, temperature, atmosphere and sintering bed. The best results are obtained when the sintering bed has the same composition to that of the sample to be sintered. The room temperature properties of the sintered materials show a K-IC value higher than 6 M Pam(1/2), comparable to those found in the literature for pressure sintered materials. (C) 1998 Elsevier Science Limited. All rights reserved.