Fabrication and properties of macro-porous SiC using Al2O3-Y2O3-SiO2 as bonding additives

Abstract

Macro-porous SiC was fabricated without using pore-forming agents by an in situ reaction bonding process. A bonding additive, Al2O3?Y2O3?SiO2, with a low melting temperature was mixed with SiC particles and sintered at 1500 ?C and 1600 ?C for 1 h in Ar. Macro-porous SiC with a porosity of 32.7?45.9%, a pore size of 3.4?4.2 ?m, and a relatively narrow and uniform pore size distribution was fabricated by varying the amount of bonding additive. The flexural strength of macro-porous SiC prepared at 1500 ?C increased from 47.2 MPa to 71.2 MPa while the porosity decreased from 45.9% to 42.8%, respectively. When the sintering temperature of the macroporous SiC was increased to 1600 ?C, the flexural strengths were significantly reduced to 32.6?35.6 MPa, along with a reduction in porosity and pore size. The permeability of macro-porous SiC prepared at 1500 ?C varied from 1.59 x 10-12 m2 to 1.26 x 10-12 m2, depending on the porosity. As the sintering temperature increased from 1500 ?C to 1600 ?C, the permeability decreased to less than 1.00 x 10-12 m2 because of the reduced porosity and average pore size. The electrical resistivity of macro-porous SiC prepared at 1500 ?C and 1600 ?C varied from 2.7 x 108 ?-cm to 1.4 x 109 ?-cm and from 1.3 x 108 ?-cm to 1.7 x 109 ?-cm, respectively, with increasing volume percent of bonding additives. The relatively high electrical resistivity was apparently due to neck bonding phase between SiC particles formed by phases consisting of Y2Si2O7, YAG, and residual Al2O3.