چكيده به لاتين
Abstract
In this research, porous silicon nitride bodies were gelcasted using starch as both geling agent and pore forming agent at the same time.This novel method, also called starch consolidation casting, have been used just for oxide ceramic bodies until now.
At the first step, effect of parameters containing surface oxidation of silicon nitride powder, amount of dispersant, solid loading and starch content on viscosity and rheological behavior of silicon nitride – starch slurry was investigated. At the end of this step stable and castable slurries were achived.
After casting and heating the slurries up to 80ᵒC, green samples with strength of 5 to 9MPa were fabricated. Sintering was carried out in an air furnace under nitride powder bed condition using 1.5 wheight percent Al2O3 and 4.5 weight percent Y2O3 as sintering additives. Two step sintering was carried out at 1650ᵒC for 2, 4 and 6 hours with and additional holding at 1420ᵒC for 1 hour. One step sintering was carried out at 1650ᵒC for 4h. effect of amount, shape and size of starch granules on the amount, shape and size of pores in sintered samples have investigated. Finally, a silicon nitride sample with 108.85MPa flextural strength and 43.98 volume percent porousity have fabricated through starch consolidation casting and pressureless sintering. Flextural strength of porous silicon nitride samples fabricated through starch consolidation casting compared with common gelcasting methods is lower because of large pores. But it is sufficient for many applications and can be improved by optimizing parameters of the process in next researches.
