Monolithic silicon carbide with interconnected and hierarchical pores fabricated by reaction‐induced phase separation

Porous silicon carbide (SiC) monoliths attract increasing attentions in catalyst/catalyst support, electromagnetic absorption, heat exchanger, hot gas separation, porous media combustion, and metal/ceramic composite areas, owing to their excellent properties including high-temperature stability, good mechanical strength, low thermal expansion coefficient, high thermal conductivity, and chemical inertness. In light of their promising applications, numerous methods have been developed for the fabrication of porous SiC monoliths, such as oxidation bonding, freeze-drying, sacrificial templating, direct foaming, and sol-gel method combined with carbothermal reduction. However, based on them, it is still not easy to build the interconnected and hierarchical porous structure, which showed improved performance compared with the single-size porous structure and was preferred in the applications for catalyst/catalyst support and hot gas separator.

In this work, hierarchically porous silicon carbide (SiC) monoliths (Fig. 1) were fabricated based on polycarbosilane (PCS), divinyl benzene (DVB), and decalin, by a sequence of procedures including catalyst-free hydrosilylation reaction-induced phase separation, ambient-pressure drying, calcination, and HF etching. The influences of ratios of each component on the phase separation were systematically studied. It was found that isotactic polypropylene added as a nonreactive additive could effectively tailor the microstructure and improve the mechanical properties of SiC monoliths. The resultant SiC monoliths mainly consisted of β-SiC nanocrystals (Fig. 2), and possessed low bulk density (0.7 g/cm3), high porosity (78%), large specific area (101 m2/g), high compressive strength (14 MPa), and hierarchical pores (macropores around 350 nm, mesopores around 4 nm and 20 nm). These properties make SiC monoliths promising materials for catalyst/catalyst support, gas separator, and the reinforcement of high-temperature composites.

Figure 1. Mechanism and route for the fabrication of silicon carbide monoliths

Figure 2. Cross-sectional SEM and TEM images after calcination at 1700 C and HF etching

Based on this technology, the researchers have applied for a Chinese patent. In addition, this work has been published in Journal of the American Ceramic Society. The first author of the article is Bo-xing Zhang (South China University of Technology). The corresponding authors are Prof. Wenfeng Qiu (South China University of Technology) and Prof. Tong Zhao (South China University of Technology).

B. Zhang, Y. Zhang, Z. Luo, W. Han, W. Qiu,* T. Zhao,* Monolithic silicon carbide with interconnected and hierarchical pores fabricated by reaction‐induced phase separation, Journal of the American Ceramic Society 2018, DOI: 10.1111/jace.16263

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Source from South China Advanced Institute for Soft Matter Science and Technology

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