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Ceramics International 37 (2011) 223–230 www.elsevier.com/locate/ceramint

Preparation of porous SiC ceramics by an infiltration technique
Atanu Dey, Nijhuma Kayal, Omprakash Chakrabarti *
Central Glass and Ceramic Research Institute, (Council of Scientific and Industrial Research) 196, Raja S. C. Mullick Road, Kolkata 700 032, India Received 18April 2010; received in revised form 15 May 2010; accepted 23 August 2010 Available online 29 September 2010

Abstract: The possibility of infiltration as a technique for synthesizing porous SiC ceramics was examined. SiC powder compacts were infiltrated with a liquid precursor which produced SiO2 during pyrolysis in air at a low temperature. Infiltrated SiO2 might act as a bond between the neighboringSiC particles at contacting points. The process parameters which control the rate of infiltration of liquid precursor to SiO2 into porous SiC powder compacts were studied. Results showed that the infiltration rate could be estimated by using weight gain measurements. Sintering infiltrated bodies at 1300 8C yielded specimens in which only silicon carbide and cristobalite were detected. The presenceof cristobalite significantly controlled the porosity as also the mechanical properties. Reasonable flexural strengths ($ 48 MPa) could be achieved at a porosity level of 26 vol.% with near uniform pore diameter of around 5 mm. # 2010 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Keywords: SiC Ceramics; Porous material; Infiltration; Silica sol

1. Introduction Currently, porous SiCceramics have been a focus of interesting research in the field of porous materials due to their excellent structural properties, high strength, high hardness, and superb mechanical and chemical stabilities, particularly at high temperatures and hostile atmospheres. Porous SiC ceramics have been considered as suitable candidate materials for catalyst supports [1,2], hot gas or molten metal filters [3],high temperature membrane reactors [4], thermal insulating materials [5], gas sensors [6] etc. Porous SiC ceramics are fabricated by various methods including partial sintering [7], carbothermal reduction [8,9], replication or pyrolysis of polymeric sponge [10–12], reaction bonding [13,14] etc. In all these methods SiC needs to be sintered which requires a very high temperature due to the strongcovalent nature of the Si–C bond, selective sintering additives, expensive atmosphere, costly equipment and delicate instrumentation. Processing of porous SiC ceramics at low temperature using a simple technique thus becomes necessary. In order to realize the low temperature fabrication of porous SiC ceramics She et al. [15]

* Corresponding author. Tel.: +91 33 2473469/3496x3473; fax: +91 3324730957. E-mail address: omprakash@cgcri.res.in (O. Chakrabarti).

developed an oxidation bonding technique in which porous powder compact of SiC was heat treated in air to promote oxidation and consequently to bind SiC particles by oxidation derived SiO2 glass. The author used graphite as a pore former [16]. The mechanical behavior of the oxidation bonded SiC was further improved by addition offine alumina powder which could react with silica with in situ formation of strong mullite bond [17]. Ding et al. [18] also reported formation of porous mullite bonded SiC ceramics following identical procedure and using a powder compact of SiC and Al2O3 formed by dry pressing. Bardhana et al. followed colloidal processing route to prepare SiC ceramics bonded with mullite formed in situ [19]. Liu etal. [20] investigated on in situ formation of cordierite for application as bonds in porous SiC ceramics. Oxide bonding of porous SiC ceramics of honeycomb structure has been reported by Morimoto et al. in which external addition of cordierite was made as a secondary bond phase [21]. Although all these methods are successful in forming oxide bond for porous SiC ceramics, they suffer from many...