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Abstract: In this paper, novel porous Si3N4 ceramics were prepared by aqueous gelcasting using Si3N4 poly-hollow microspheres as pore-forming agent. The effect of Si3N4 poly-hollow microsphere content on the phase composition, microstructure, shrinkage, porosity and mechanical properties of the prepared porous Si3N4 ceramics were investigated. It is found that there is only β-Si3N4 phase in all the prepared porous Si3N4 ceramics. Meanwhile, the SEM results show that the pores in the porous Si3N4 ceramics distribute uniformly, the added Si3N4 poly-hollow microspheres and the basal body contact closely. With the increase of Si3N4 poly-hollow microsphere content, the shrinkage of the porous Si3N4 ceramics decreases gradually, and the porosity of the porous Si3N4 ceramics decreases firstly and then increases. Furthermore, the flexural strength and fracture toughness of the porous Si3N4 ceramics decrease with the increase of the Si3N4 poly-hollow microsphere content. [Copyright &y& Elsevier]

Indirect selective laser sintering (SLS) was combined with reactive melt infiltration (RMI) to fabricate RB-SiC, and the effects of preform impregnation with different carbon source on the carbonized sample and final RB-SiC were investigated. Results show that the impregnation treatment led to increased bulk density and mechanical strength of samples at all stages. The pore size dwindled and the porosity decreased significantly for the carbonized sample, and the content of Si reduced for the final RB-SiC. The impregnation with PF resin containing 30 % nano carbon black (PFnanoC) seems more promising for the comprehensive properties improvement, the final RB-SiC had a relatively fewer amount of residual pore and carbon and showed superior mechanical properties compared with those of sample impregnated with only PF resin. Kinetics analysis indicates a slower pore-clogging rate under the PFnanoC impregnation condition, which avoided or hindered a too-early infiltration cease during the RMI process. [ABSTRACT FROM AUTHOR]