Hongjiao Lin

Anti-oxidation property of the ZrB2–SiC–Si-coated low-density C/C composites

ABSTRACT ZrB2–SiC–Si-coated low-density C/C composites were prepared by a low-cost and simple pack cementation. The microstructure, oxidation and ablation resistance of the ZrB2–SiC–Si-coated low-density C/C composites have been investigated. The ZrB2–SiC–Si-coated low-density C/C composites exhibited good oxidation, thermal shock and ablation resistance at high temperature. The mass loss of the coated low-density C/C samples was only 0.68% at 1773 K for more than 260 h. The mass gain of the coated low-density C/C samples was 1.5% after 50 thermal cycles. The coated low-density composites could also withstand from ablation at 2573 K for 60 s under oxyacetylene flame. The good oxidation and ablation resistance of the composites are mainly attributed to the interlocking-pattern structure and the protection of the oxide layer.

Synthesis and characterisation of self-assembled SiC nanowires and nanoribbons by using sol–gel carbothermal reduction

ABSTRACT Hexagonal-shaped 3C-SiC nanowires were grafted onto SiC nanoribbons by a sol–gel technique using ferrocene as catalyst. The nanowire diameter (∼200 nm) and the nanoribbon width–thickness ratio (20:1) are uniform along their entire length. Their length is about several tens to several hundreds of micrometres. Meanwhile, single SiC nanostructure (nanowire or nanoribbon) was obtained by adjusting temperature field. A novel cooperative growth mechanism of vapour–liquid–solid and vapour–solid was proposed for the self-assembled SiC nanostructure. The self-assembled SiC nanowires and nanoribbons exhibit two strong broad photoluminescence peaks at wavelengths of about 373 and 471 nm, which are significantly shifted to the blue compared with the reported luminescence of SiC nanowires. This study will pave a way for the controllable synthesis of SiC nanowires and nanoribbons, and provide a simple method to connect them together firmly as potential applications for nanodevices in future.

Simultaneously improving the mechanical strength and electromagnetic interference shielding of carbon/carbon composites by electrophoretic deposition of SiC nanowires

C/C composites with both high specific strength and excellent electromagnetic shielding efficiency are required for advanced space applications. For this purpose, SiC nanowires (SiCNWs) were introduced in C/C composites by electrophoretic deposition. The presence of SiCNWs in C/C induces the formation of a SiCNW/pyrocarbon coaxial structure, which refines the matrix and decreases the stress concentration of the matrix. The average flexural strength of C/C composites increases by ∼100% after adding SiC nanowires due to enhanced interlaminar bonding after introducing the nanowires. Meanwhile, the average electromagnetic shielding efficiency in the X band (8.2–12.4 GHz) increases from 35.6 dB to 60.5 dB with an optimized nanowire content. Reflection is the predominant mechanism for electromagnetic shielding while introducing SiC nanowires also enhances the electromagnetic absorption within the composites. As pyrocarbon in the SiCNW–pyrocarbon coaxial structure shows a higher degree of crystallization, the coaxial structure increases the electron loops in the matrix and greatly improves reflection at high frequency. Also, the absorption of electromagnetic waves inside the composites is enhanced by introducing SiCNWs due to the increase of electron hopping among interfaces. This work proves that introducing SiC nanowires is promising in fabricating lightweight C/C composites with excellent mechanical and electromagnetic properties.