Yehong Cheng

In Situ Growth of Core–Sheath Heterostructural SiC Nanowire Arrays on Carbon Fibers and Enhanced Electromagnetic Wave Absorption Performance

Large-scale core-sheath heterostructural SiC nanowires were facilely grown on the surface of carbon fibers using a one-step chemical vapor infiltration process. The as-synthesized SiC nanowires consist of single crystalline SiC cores with a diameter of ∼30 nm and polycrystalline SiC sheaths with an average thickness of ∼60 nm. The formation mechanisms of core-sheath heterostructural SiC nanowires (SiCnws) were discussed in detail. The SiCnws-CF shows strong electromagnetic (EM) wave absorption performance with a maximum reflection loss value of -45.98 dB at 4.4 GHz. Moreover, being coated with conductive polymer polypyrrole (PPy) by a simple chemical polymerization method, the SiCnws-CF/PPy nanocomposites exhibited superior EM absorption abilities with maximum RL value of -50.19 dB at 14.2 GHz and the effective bandwidth of 6.2 GHz. The SiCnws-CF/PPy nanocomposites in this study are very promising as absorber materials with strong electromagnetic wave absorption performance.

Enhanced mechanical, thermal, and electric properties of graphene aerogels via supercritical ethanol drying and high-temperature thermal reduction

Graphene aerogels with high surface areas, ultra-low densities and thermal conductivities have been prepared to exploit their wide applications from pollution adsorption to energy storage, supercapacitor, and thermal insulation. However, the low mechanical properties, poor thermal stability and electric conductivity restrict these aerogels’ applications. In this paper, we prepared mechanically strong graphene aerogels with large BET surface areas, low thermal conductivities, high thermal stability and electric conductivities via hydrothermal reduction and supercritical ethanol drying. Annealing at 1500 °C resulted in slightly increased thermal conductivity and further improvement in mechanical properties, oxidation temperature and electric conductivity of the graphene aerogel. The large BET surface areas, together with strong mechanical properties, low thermal conductivities, high thermal stability and electrical conductivities made these graphene aerogels feasible candidates for use in a number of fields covering from batteries to sensors, electrodes, lightweight conductor and insulation materials.

Ordered Silica Nanoparticles Grown on a Three-Dimensional Carbon Fiber Architecture Substrate with Siliconborocarbonitride Ceramic as a Thermal Barrier Coating

Hierarchical structure consisting of ordered silica nanoparticles grown onto carbon fiber (CF) has been fabricated to improve the interfacial properties between the CFs and polymer matrix. To improve the reactivity of CFs, their surface was modified using poly(1,4-phenylene diisocyanate) (PPDI) via in situ polymerization, which also resulted in the distribution of numerous isocyanate groups on the surface of CFs. Silica nanoparticles were modified on the interface of CF-PPDI by chemical grafting method. The microstructure, chemical composition, and interfacial properties of CFs with ordered silica nanoparticles were comprehensively investigated by scanning electron microscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. Results indicated an obvious increase in the interfacial shear strength, compared to that of CF precursor, which was attributed to silica nanoparticles interacting with the epoxy resin. Furthermore, siliconborocarbonitride (SiBCN) ceramic was used as thermal barrier coating to enhance 3D CF architecture substrate antioxidant and ablation properties. Thermogravimetric results show that the thermal stability of the CF with SiBCN ceramic layer has a marked increase at high temperature.

A ZrB2–SiC/SiC oxidation protective dual-layer coating for carbon/carbon composites

ABSTRACT In order to improve the oxidation resistance of C/C composites, a ZrB2–SiC/SiC oxidation protective dual-layer coating was prepared by a pack cementation combined with the slurry paste method. The phase and microstructure of the coating were characterised by X-ray diffraction, scanning electron microscope and energy-dispersive spectrometer analyses. The anti-oxidation and thermal shock resistance of the coating were also investigated. It was found that the ZrB2–SiC/SiC coating could effectively improve the oxidation resistance of the C/C composites. The weight loss of the coated samples was only 1.8% after oxidation at 1773 K for 18 h in air. The coating endured 20 thermal shock cycles between 1773 K and room temperature with only 4.6% weight loss.

Hot corrosion resistance of Zrb2-based ceramic composites against NaCl molten salt

Abstract Hot corrosion resistances of ZrB2–SiC–C ceramic composites were studied at 1000°C in molten NaCl. Results indicated that the sample underwent a slight corrosion. Both macrograph and microstructure of the composites exhibited no obvious change. The ZrB2–SiC–C composite showed good resistance to [Cl−] corrosion in high temperature.

Spark plasma sintering of B4C–ZrB2 and B4C–ZrB2–SiC ceramics

Abstract Micrometre-sized B4C powder added with ZrB2 powder or the mixed powders of ZrB2 and SiC were sintered by spark plasma sintering under the load of 30 MPa at 1950°C for 18 minutes. The microstructure and mechanical properties of the composites were investigated. The B4C-20 vol.-% ZrB2 composite showed the highest flexural strength and fracture toughness of 489 MPa and 4·8 MPa·m1/2, were obtained of the B4C-20 vol.-%ZrB2 composite and which were much higher than those of monolithic B4C ceramic. The Vickers hardness of B4C composites ranged from 28·9 to 34·6 GPa. The toughening mechanisms have been analysed because of the deflection of microcrack along with the grains boundary and the mismatch of coefficient of thermal expansion between matrix and additions. Besides, the addition of ZrB2 and SiC was observed to enhance the electrical conductivity and electron discharge machining performance of B4C composites.