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 sl ips was optimized by dispersing with TMAH up to pH 11.5 using different mix ing procedures and including different concentrations of sintering aids (Al 2O3 and Y(2)O3). rn this part, the obtention of pressureless sintered silic on nitride bodies by colloidal filtration techniques is studied. The kineti cs of the different compositions is studied for both slip casting and press ure casting. The pressure casting kinetics is up to 20 times faster than th at of slip, casting, which allows the scale-up of the process for a low cos t production, The obtained green density is slightly >58%th for slip castin g and 57-55%th for pressure casting, depending on the applied pressure. Thi s 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. T he best results are obtained when the sintering bed has the same compositio n 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), comparab le to those found in the literature for pressure sintered materials. (C) 19 98 Elsevier Science Limited. All rights reserved.