PREPARATION OF ZIRCONIUM PHOSPHATE BONDED SILICON NITRIDE POROUS CERAMICS REINFORCED BY IN-SITU REACTED SILICON NITRIDE NANOWIRES

In our previous study, ZrP2U7 bonded Si3N4 porous ceramics with controlled porosity (porosity > 50 %) are prepared. But the bending strength of the obtained materials is too low to apply. In this paper, Si3N4 porous ceramics with high porosity (porosity > 50%) and elevated mechanical properties are prepared by presureless sintering technique, using in-situ reacted Si3N4 nanowires (SNNWs) as a reinforcement. In these porous ceramics, pores with a pore size of less than 0.5 urn are formed by the continuous reaction of Y , I at 250 degrees C and pores with the pore size of-10, are formed by the burnout of starch at -550 degrees C. Finally, SNNWs reinforced porous ceramics are sintered at 1300 degrees C. The results suggest that the porosity of the obtained S13N4 porous ceramics is in the range of 50-55 %. a-Si3N4 is the major phase, keeping the character of S13N4 raw material. It is observed that the SNNWs with the diameter of less than 50 nm and the length of 2.5-10 , are formed in S13N4 porous matrix, in the pore wall area and within the pores. The bending strength of S13N4 porous ceramics increase significantly from 22 MPa to 39 MPa when the SNNWs content is 4 vol.%, while the porosity could maintains at 52 %, indicating that the mechanical properties of the S13N4 porous ceramics can be well enhanced by SNNWs.