Processing highly porous SiC ceramics using poly(ether-co-octene) and hollow microsphere templates

Ceramic components with high porosity, high strength, andgood permeability are especially required for hot-gas andmolten metal filters, catalyst supports, preforms for makingmetal matrix composites, gas burner media, and light-weight structural parts [1–8]. Silicon carbide (SiC) hasbeen considered a candidate material for hot-gas filters dueto its unique combination of such properties as high ther-mal conductivity, superior mechanical features, high ther-mal shock capacity, and corrosion resistance [9–13].Highly porous (porosity C 80%) SiC ceramics are pre-pared using the following processing methods: (1) immer-sion of the polyurethane (PU) foams in a ceramic slurry,and drying, burning out the PU, and then sintering [1, 5,14]; (2) freezing of gel containing SiC powders [4]orfreezing the polycarbosilane/camphene solution [15]; (3)gel-casting of SiC powder mixtures using agar as the gel-ling agent [16]; and (4) pyrolysis of a cross-linked bodyconsisting of a polycarbosilane precursor and polymermicrobead templates [17], or pyrolysis and carbothermalreduction of a cross-linked body consisting of a polysi-loxane precursor, polymer microbead templates, phenolresin, and optional sintering additives [18].The recent research studies indicate that highly porousceramic structures can be prepared by the compoundingand pyrolysis of polysiloxane and low density polyethelene(LDPE) blends [19, 20]. The processing temperature usingLDPE was 110–140 C. Polysiloxane is likely to cross-linkat such high temperatures [21], and the cross-linked poly-siloxane structure will in turn suppress the LDPE phasedispersion in the polysiloxane phase. Moreover, under highshear conditions, the dispersed polymer phase will tend toagglomerate again due to the rapid relaxation of thepolymer chain at high processing temperatures. Poly(ether-co-octene) (PEOc) is a type of thermoplastic elastomerwith a low melting point (melting peak around 60 C), highmolecular weight, and low crystallinity [22]. Thus, theconsequences of the high-temperature cross-linking ofpolysiloxane can be avoided during blending, and thedegree of co-continuous structure and mechanical proper-ties can be improved by using polysiloxane–PEOc polymerblends.This study describes a new method of preparing highlyporous SiC ceramics using polysiloxane, PEOc, and hollowmicrosphere templates. Commercially available polysilox-ane (YR3370, softening point: 109 C, melting point:*155 C GE Toshiba Silicones Co., Ltd, Tokyo, Japan), acarbon black (Corax MAF, Korea Carbon Black Co., Ltd.,Inchon, Korea), a-SiC (FCP15C, Norton AS, Lillesand,Norway), hollow poly(methyl methacrylate) microspheres(461DU40, Expancel, Sundsvall, Sweden), PEOc (metal-locene catalyzed copolymer of ethylene and 1-octene,Engage 8200, melting peak: 63.0 C, Dow Chemical Co.,Michigan, USA), AlN (Grade F, 1.3 lm, Tokuyama Soda.,Tokyo, Japan), and Y