Guangdong Zhao

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.

Graphene nanosheet reinforced ZrB2–SiC ceramic composite by thermal reduction of graphene oxide

A graphene nanosheet reinforced ZrB2–SiC ceramic composite (GNs/ZrB2–SiC) using graphene oxide (GO) was hot pressed at 1950 °C and 30 MPa for 1 h. Raman and XPS analysis showed multilayer GNs structures were successfully introduced into the composite by in situ thermal reduction of GO during the hot pressing process. The homogeneous dispersion of GO guaranteed the uniform distribution of GNs structures in the composite. Mechanical properties such as bending strength, fracture toughness and hardness were studied for the ZrB2–SiC composite with different volumes fraction of GO. The addition of approximately 5 vol% graphene nanosheets improved the fracture toughness of ZrB2–SiC up to 7.32 MPa m0.5, and the strength was also raised to 1055 MPa. The toughening mechanisms were graphene crack bridging and pulling out induced crack deflection in the GNs reinforced composite.

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.

Preparation, characterization, and properties of graphene-based composite aerogels via in situ polymerization and three-dimensional self-assembly from graphene oxide solution

Three-dimensional reduced graphene oxide/phenolic resin (RGO/PR) composite aerogels were synthesized through a simple and facile one-pot polymerization-induced phase separation (PIPS) of a phenolic prepolymer with hexamethylenetetramine (HMTA) as a catalyst in an ethylene glycol (EG) suspension of graphene oxide (GO), followed by solvent exchange and ambient pressure drying. The RGO/PR composite aerogels showed an interpenetrating framework with high meso- and macroporosity. By adjusting the amounts of GO in the co-precursor solution, aerogels with different textural properties were prepared. A self-assembly mechanism based on the adsorption and chemical interactions between GO sheets, PR and HMTA, as well as PIPS in the precursor solution was proposed to explain the formation of the composite aerogels. Furthermore, enhancement of GO on the thermal stability of the RGO/PR composite aerogels were studied, the characteristic thermal degradation temperature and char yield of the RGO/PR composite aerogels are higher than that of the as-prepared PR aerogels. The anchored effect of chemical bonds and π–π stacking of PR polymer chains at the interface of GO sheets and PR resin, and the induced effect of GO on PR char formation and graphitization should be a contributing factor to the enhancement. Graphene/carbon composite aerogels were also fabricated by carbonization of the aerogels at 1000 °C in argon. A hierarchical porous microstructure with large micropores was achieved by pyrolysis gas evolution, phenolic particle shrinkage and preservation of the meso- and macroporous structure during the carbonization.

Carbon Nanofiber Arrays Grown on Three-Dimensional Carbon Fiber Architecture Substrate and Enhanced Interface Performance of Carbon Fiber and Zirconium Carbide Coating

Carbon nanofibers (CNFs) were grown around the carbon fiber architecture through a plasma enhanced chemical vapor deposition method to enhance the interface performance between CF architecture substrate and ZrC preceramic matrix. The synthesized 3D CF hierarchical architectures (CNFs-CF) are coated with zirconium carbide (ZrC) ceramic to enhance their antioxidant property and high temperature resistance. The composition and the crystalline phase structure of the composite were detected with the X-ray photoelectron spectroscopy and X-ray diffraction. The results of scanning electron microscopy show that, the as-prepared CNFs and consistent ZrC ceramic coating are uniformly covered on the surface of carbon fiber architecture substrate. The ZrC ceramic products with excellent crystallinity were got from the pyrolysis of preceramic polymer at 1600 °C in inert atmosphere. Comparing with the untreated CF, the loading of ZrC ceramics around the CNFs-CF architecture surface are significantly increased. The thermal stability and mechanical property of CNFs-CF/ZrC nanocomposites have been promoted obviously compared with the CF/ZrC ceramic nanocomposite. The prepared CNFs-CF/ZrC ceramic nanocomposite is one of the potential candidate materials for the thermal protection application.

Multifunctional Thermal Barrier Application Composite with SiC Nanowires Enhanced Structural Health Monitoring Sensitivity and Interface Performance

Carbon fiber (CF)-reinforced ceramic composites show the attractive potential for next generation thermal protection materials because of their outstanding reliability and excellent high-temperature resistance but are facing great challenges in the combination of the engineering practicality and versatility. Herein, it is demonstrated that silicon carbide nanowires can be grown on the surface of CF to create a multifunctional thermal barrier application composite. The embedding of the silicon carbide nanowires in the interface of CF and ceramic matrix significantly increased the structural health monitoring sensitivity and interface strength of the composites. Compared to the conventional CF/ZrC composites, the structural health monitoring sensitivity of the composites with SiC nanowires is greatly elevated with a 14-fold improvement. Additional investigations revealed that the multifunctional SiCnws-CF/ZrC nanocomposites enjoyed a low thermal conductivity of 0.49 W/(m·K), a light weight (0.76-1.85 g/cm3), and a relative high compressive strength of 23.64 MPa, which is favorite in applying as a thermal barrier material. Furthermore, the interface design strategy could be extended as a universal method in fabricating various fiber-reinforced composites for a wide range of other applications.

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.