STUDIES ON PERMEABILITY PROPERTIES AND PARTICLE CAPTURE EFFICIENCIES OF POROUS SiC CERAMICS PROCESSED BY OXIDE BONDING TECHNIQUE

Abstract

Porous SiC ceramics bonded with mullite MBS of fractional porosity (epsilon) of 0.29-0.56, average pore size (d(pore)) of 5-11 mu m, flexural strength (sigma) of 9-34 MPa, and elastic modulus (E) of 7-28 GPa] and cordierite (CBS with epsilon of 0.33-0.72, d(pore) of 6-50 mu m, sigma of 5-54 MPa, and E of 6-42 GPa) were prepared by heating in air at 1350-1500 degrees C compacts of desired amounts of SiC, Al2O3, and MgO powders and petroleum coke dust as the pore former. Air permeation behavior of well-characterized samples was studied with fluid superficial velocity (v(s)) from 0.08 to 1.0 m s(-1) and at RT to 750 degrees C. The Darcian (k(1)) and non-Darcian (k(2)) permeability coefficients were evaluated by fitting the Forchheimer's equation to experimental pressure drop-superficial velocity data. Porosity dependence of permeability coefficients was explained in terms of structural characteristics. Changes in pressure drop experienced by the porous ceramics at high temperatures were explained by temperature dependence of permeability coefficients and variation of fluid properties. Collection efficiency (E-overall) of filter ceramics operating on removal of solid NaCl nanoaerosol particles (of 7-300 nm size) was determined from particle counts before and after filtration at v(s) = 0.05-0.10 m s(-1). Experimental results showed variation of E-overall from 96.7 to 99.9% for change of epsilon from 0.56 to 0.68. The size-selective fractional collection efficiency at different porosity levels was derived using the well-known single-collector efficiency model considering some boundary conditions and the model data were validated with experimental results. The test results were used to examine the applicability of the filter ceramics in nanoparticle aerosol filtration processes.