Fabrication Of 3-D Interconnected Macroporous Silicon Carbide

Silicon carbide (SiC) ceramics with 3-D interconnected macroporous structures themselves can not only be used as filters and membranes in harsh conditions, absorbents, insulator panels, physical and chemical sensors, etc., but also can be used as matrix for fabricating composite materials. In view of this, increasing attention has been paid to the development of viable fabrication methods.In this paper, the different fabrication methods for macroporous silicon carbide ceramics were attempted, including the non-templated and templated ones. For non-templated method, this work puts forward a novel process combining the decompression process with previously developed PAF (PVA-assisted pore-forming) method. The influence of the mass ratios of SiC to PVA, surfactant contents and volume expansion ratios on the pore structure and size was studied. For templated method, we investigated the influence of adhesive and defoaming agent on the pore structure of 3-D SiCs using polyurethane (PU) foam as hard template. Aimed at attenuating the hole defects in the struts left by the decomposition of PU foam,3-D SiCs can be obtained with minimized strut pores via one kind of phenolic resin assisted carbonization process.Main results are as follows:PAF method can improve the interconnectivity between macropores in the 3-D SiCs by changing the stirring rates, surfactant contents and concentrations of PVA, while is not able to further increase the pore diameters of 3-D SiCs exceeding 0.3 mm; Decompression method once combining with the PAF method can lead to the 3-D SiCs with pore sizes range from 0.5 mm to 1.0 mm by simply altering the mass ratios of SiC and PVA, the volume expansion ratios and surfactant contents. The maximum average pore size can reach 0.95 mm. Considering the pore size and uniformity in the pore size distributions, the optimal experimental conditions are:w(SiC)/w(PVA) ratio of 0.32, the volume expansion of three times. The porosity and compressive strength of 3-D SiCs thus obtained are 83.82% and 1.8 MPa, respectively; based on the coating method using PU as hard template, controlling of the contents of adhesive and defoaming agent can lead to SiC slurries with high solid content, good fluidity and thixotropy. The problems of cracking and existence of a large number of air bubbles can be solved. The maximum compressive strength of 3-D SiCs thus obtained is 0.52 MPa; It has been confirmed that the carbon skeleton can be obtained by carbonizing the impregnated PU foam in ethanolic solution of phenolic resin. Following silicization by liquid silicon transformed the 3-D carbon into 3-D SiC. The 3-D SiCs faithfully duplicating the 3-D networked structure of PU foam can eventually be obtained, importantly with significantly reduced strut pores. The work could pave the way for the future development of 3-D porous SiC ceramics.