Porous SiC ceramics were synthesized by oxidation bonding of compacts of commercial α‐SiC powder at 1300°C. Different volume fractions of petroleum coke powder were used for variation of porosity of ceramics from 36% to 56%. The material exhibited variations of pore size from 3 to 15 μm, flexural strength from 5.5 to 29.5 MPa, and elastic modulus from 3.3 to 27.6 GPa. Air permeation behavior was studied at 26–650°C. At room temperature Darcian (k1) and non‐Darcian (k2) permeability parameters vary from 1.64 to 18.42 × 10−13 m2 and 0.58 to 2.95 × 10−7 m, respectively. Temperature dependence of permeability was explained from structural changes occurring during test conditions.

Cordierite bonded porous SiC ceramics having pore fractions (ε) between 0.33 and 0.72 and pore sizes of 6−50 μm, flexural strength of 5−54 MPa, and elastic modulus of 6−42 GPa were prepared by oxide bonding at 1350 °C in air compacts of SiC, Al 2 O 3 and MgO powders with petroleum coke (PC) as the sacrificial pore former. To test the applicability of the porous ceramics in the fluid flow field, air permeation behavior was studied with fluid superficial velocity from 0.083 to 0.90 m s −1 and at 26−750 °C. The Darcian, k 1 , and the non-Darcian, k 2 , permeability coefficients were evaluated by fitting Forchheimer's equation to the experimental results. The temperature dependence of the permeability coefficients was explained from structural changes occurring during test conditions. The collection efficiency of filter ceramics (ε = 0.62−0.68) operating on removal of nanosized aerosol particles with sizes varying from 7 to 300 nm was determined by counting particles before and after filtration at a fluid superficial velocity of 0.1 m s −1 . Experimental results showed variation of collection efficiency from 96.7 to 99.9%. The size-selective fractional collection efficiency at different porosity levels was derived by using the well-known singlecollector efficiency model considering some boundary conditions, and the model data were validated with experimental results. The test results were used for examination of the applicability of the filter ceramics in nanoparticle filtration processes.

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A theoretical relation between processing parameters and porosity (29-56%) of mullite-bonded porous SiC ceramics was derived and validated with experimental data. Porosity-dependent variation of fracture strength (9-34 MPa) and elastic modulus (7-28 GPa) was explained by the minimum solid area model. At room temperature, the Darcian, k 1 (1.2 9 10 À13 -1.6 9 10 À12 m 2 ) and the non-Darcian, k 2 (4.6 9 10 À9 -2.7 9 10 À7 m) permeability coefficients showed linear variation with porosity. Tests conducted up to 650°C indicated an increase in k 1 with temperature and a reverse trend for k 2 . Airborne NaCl nanoparticle filtration tests showed good performance of SiC ceramics with fractional collection efficiency of >99% at 46-56% porosity levels.*omprakash@cgcri.res.in

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