In order to improve the connectivity between pores of gelcasted and solid-state-sintered SiC (S-SiC) foams, we utilized the synergetic poring mechanism of direct foaming and sacrificial solid template through introducing organic micro-beads into aqueous foamed SiC-B 4 C-C suspensions. The addition of micro-beads accelerated the formation of more bubble-derived pores in S-SiC foams, and generated abundant bead-derived pores in the bubble-derived-pore struts and partial-sintering-derived pores between SiC grains as well. This multiple pore microstructures induced excellent connectivity between pores and an ultrahigh porosity of 89.5%. Consequently, an outstanding nitrogen gas permeability of 9.2 × 10 −11 m 2 was acquired under the condition of a superior compressive strength of 2.2 ± 0.4 MPa.
Hao Xiong,Anze Shui,Qingliang Shan,Shenghui Zeng,Xiuan Xi,Bin Du
Polishing porcelain stoneware tile residues (PPR) is used to prepare foamed ceramic to solve the problem of solid waste discharge in ceramic industry. In this study, C, Al and Si powder were added to the simulated PPR to control foaming, and the mechanism of silicon carbide foaming in the PPR was discussed in detail. After these powders were introduced into the simulated PPR, the phenomenon of alumina crystallization on the pore wall of the foamed ceramic and the diffusion of gas in the foamed ceramic were discovered to be exciting. The foaming mechanism of PPR is detailed as follows: the diffusion rate of oxygen in silicate liquid is faster than that of CO during sintering, so the CO generated by incomplete oxidation of silicon carbide in PPR accumulates in the liquid, which makes the volume of ceramics expand and causes foaming.
ZrB 2 –SiC foams were prepared from composite poring mechanisms of foaming and solid poring (PAA beads) by the application of a gelcasting technique. The porosities and microstructures of sintered bulks were tailored through changing the solids loading of slurries and the amount of added PAA beads. The increase in solid loading caused high viscosities of slurries, and thus resulted in the reduction of porosity and a tendency to form close pores. With increasing the amount of PAA beads, high porosities (up to 91.4%) and obvious connectivity improvement between bubble-derived pores emerged owing to efficient foaming and presence of bead-derived pores. As the porosity increased, the compressive strength (0.4–8.2 MPa) decreased, and the gas permeability (9.7–62.1×10 −12 m 2 ) augmented because of the effects of bead-derived pores and the increase in window number and size of bubble-bead pores.
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