Improving the strength and oxidation resistance of phenolic resin derived pyrolytic carbons via Cu-catalyzed in-situ formation of SiC@SiO2

Abstract

Silicon carbide (SiC) whiskers were synthesized by a facile catalyst reaction. Phenolic resin and silicon powders were the raw materials, and cupric nitrate (Cu(NO3)2) was a catalyst precursor under a reducing atmosphere at 1200 °C. The whiskers with Cu(NO3)2 catalyst had a core-shell structure. The inner nanowire had a diameter about 15 nm, and the external structure had a thickness of 38–65 nm. Upon increasing the as-calcined temperature, the thickness of SiO2 shell decreased, and the diameter of the SiC core increased. The copper oxide (CuO) phase derived from Cu(NO3)2 was reduced to copper (Cu) by gases during the process of pyrolysis phenolic resin. Cu played a pivotal role in SiC whiskers formation and its morphology control. The Cu/Si alloy was formed by Cu dissolving with Si, and this step triggered a chain reaction to promote the production of more silicon monoxide (SiO). With the Cu(NO3)2 catalyst, the synthesis mechanism of SiC whiskers transformed from vapor-liquid-solid (V-L-S) to vapor-solid (V–S). The transformation of single carbon bonding phase into C–SiC/SiO2 combined bonding phases to generate much more amount of unique C–SiC/SiO2 interfaces improved the strength and oxidation resistance of the pyrolytic carbons of the phenolic resin.