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To further improve the oxidation resistance of PDC (Polymer Derived Ceramic) composites in harsh environments, Cf/SiC/SiHfBOC composites were prepared by CVI (Chemical Vapor Infiltration) and PIP (Precursor Impregnation Pyrolysis) methods. The weight retention change, mechanical properties, and microstructure of Cf/SiC/SiHfBOC before and after oxidation in air were studied in detail. Microscopic analysis showed that only the interface between the ceramic and fibers were oxidized to some extent and hafnium had been enriched on the composite surface, after oxidation at different oxidation environments. After Cf/SiC/SiHfBOC composites oxidized at 1500 ℃ for 60 min, it was mainly determined by the HfO2 and HfSiO4 phase. Moreover, the weight retention ratio and compressive strength of the Cf/SiC/SiHfBOC composites are 83.97 % and 23.88 ± 3.11 MPa, respectively. It indicates that the Cf/SiC/SiHfBOC composites can be used for a long time in the oxidation environment at 1500 ℃.

Although axially aligned fibrous monolithic ceramics have superior mechanical properties in ceramic fiber axial direction, the obvious anisotropy in physical and chemical properties of fibrous monolithic ceramics predetermine the significant on-axis and off-axis discrepancy. The existing ZrB2-based fibrous monolithic ceramics were all arranged by axially aligned ceramic fibers. Non-axially aligned ZrB2-SiC/ZrB2-SiC-graphene short fibrous monolithic ceramics with isotropic in-plane properties were fabricated by hot pressing of disorderly-arranged short ZrB2-SiC/ZrB2-SiC-graphene fibers to overcome in-plane anisotropy of the ZrB2-based fibrous monolithic ceramics. ZrB2-SiC/ZrB2-SiC-graphene short fibrous monolithic ceramics have remarkable increase in fracture toughness, critical crack size and work of fracture compared with ZrB2-SiC ceramics. The toughening mechanism of ZrB2-SiC/ZrB2-SiC-graphene short fibrous monolithic ceramics include macroscopic toughening of crack deflection, crack branching, interface friction and ZrB2-SiC cell extraction, and microscopic toughening of graphene bridging and pull-out.

Graphene is one of the important candidates in ceramic toughening due to its outstanding physical and chemical properties. For the weak interface toughening of large-diameter graphene sheet and alleviation of the interfacial reaction between ceramic precursors and graphene sheets during high-temperature pyrolysis, ZrC–SiC‒Graphene composite was synthesized via a facile technology of infiltrating ceramic slurry instead of ceramic precursor into macroporous graphene network and spark plasma sintering. The incorporation of the graphene network improved fracture toughness, critical crack size, and fracture energy of ZrC–SiC ceramic. The multiple length-scale toughening mechanisms of ZrC–SiC‒Graphene composite include the macroscopic toughening mechanism of crack deflection and bifurcation and the micro toughening mechanism of graphene bridging, ceramic micro zone tearing, graphene pull-out, graphene and ceramic brick slipping.

SiC nanowires (SiCnws) were incorporated in supercritical-ethanol-dried graphene aerogel (GA–S) via chemical vapor infiltration (CVI) to fabricate a lightweight, thermostable, high-performance electromagnetic (EM) absorbing composite. The SiCnws improved the yield strength of GA–S from 0.15 MPa to 0.47 MPa in the linear elastic region. The oxidation temperature of GA–S contained in situ grown SiCnw exceeded 660 °C in air. The double-scale surface roughness increases the water contact angle from 53° of GA–S to 134° of SiCnw/GA–S. The SiCnw/GA–S composite showed a minimum EM wave reflection loss (RL) value of −54.8 dB at 5.3 GHz with thickness of 3.63 mm. The SiCnw/GA–S sample demonstrated a wide effective absorbing bandwidth of 6.5 GHz from 9.3 to 15.8 GHz at thickness of 2.0 mm. In addition, the SiCnw/GA–S sample could achieve effective absorption covering the entire X-band in a wide thickness range of 2.2–2.7 mm. Three-dimensional networks and residual oxygen functional groups of GA–S, the high-density stacking faults, and the abundant interfaces between SiCnws and graphene sheets played important roles in enhancing the EM dissipation of SiCnw/GA–S composites. The SiCnw/GA–S composites are promising EM-wave-absorbing materials in extreme environment.

Silicon oxycarbide (SiOC) ceramic aerogels in mesopores range have been fabricated by pyrolyzing polycarbosilane aerogels in nitrogen (N 2 ) atmosphere. The reactants, poly(methylhydrosiloxane) and 2, 4, 6, 8-tetramethyl-2, 4, 6, 8-tetravinylcyclotetrasiloxane have been heated in the presence of hydrochloroplatinic acid. As-prepared SiOC preceramic aerogel has specific surface area of 299 m 2 /g at room temperature, and decomposes during pyrolysis. Structural evolution of the aerogels as a function of heat-treatment temperature has been investigated by Fourier transform infrared spectrophotometer, X-ray diffraction analysis, transmission electron microscopy and X-ray photoelectron spectroscopy. Results indicate that tetrahedral Si–O–C network underwent four structural changes during thermal treatment from room temperature to 1600 °C.

This paper presents a double-layered coating system consisting of MoSi2 ceramic reinforced with SiC whiskers and a MoSi2-TaSi2 ceramic coating reinforced with SiC whiskers. This system improves oxidation resistance of carbon-bonded carbon fiber (CBCF) composites. Double-layer coating was about 160 µm in thickness and no interfaces or cracks between the layer and matrix were observed. Isothermal oxidation tests revealed that as-prepared coating presented excellent oxidation resistance, which could protect CBCF composites at 1500 °C for 160 min with 0.02% weight loss, whereas weight loss of single MoSi2 ceramic coating reinforced with SiC whiskers reached 0.08%. High-temperature resistance barrier of the glassy phase and Ta2O5 had a positive effect on improving the oxidation resistance of double-layer coating.

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 ...

Multi-composition coating consisting of multilayer MoSi 2 -SiC w -SiB 6 -borosilicate glass/TaSi 2 -MoSi 2 -SiC w -SiB 6 -borosilicate glass has been prepared on the surface of SiOC ceramics-modified carbon bonded carbon fiber composites by a rapid sintering method. Arc jet test has been utilized to evaluate the oxidation-resistance ability from room temperature to 1800 K during the total exposure time between 1000 s and 1500 s. The experimental results show that the multilayer coating can form a robust oxidation protection layer to protect M-CBCF substrates effectively. The surface temperatures of tested samples reach 1573–1973 K and mass ablation rates of the samples vary from 1.23 × 10 −6 g/s cm 2 to 9.39 × 10 −6 g/s cm 2 .

To improve the ablation resistance of graphite, ZrB 2 SiC/SiC coating was prepared by pack cementation. Ablation resistance of the coating was investigated by oxyacetylene torch. After ablation for ∼200 s, the linear and mass ablation rates of ZrB 2 SiC/SiC coated graphite at center area were 4.647 μm/s and 1.216 mg/s, respectively. During ablation process, chemical erosion and particle denudation occurred at the same time were the main factors leading to ablation.

Hierarchical structure consisting of graphene oxide (GO) grafted onto carbon fiber (CF) has been synthesized to improve the interfacial properties between the CFs and polymer matrix. The modified CFs are coated with siliconborocarbonitride (SiBCN) preceramic polymer by in situ polymerization to enhance their antioxidant and ablation properties. X-ray photoelectron spectroscopy were used to monitor the composition of the composites. Scanning electron microscopy images revealed that GO was successfully grafted onto CF (CF-g-GO) and coated with SiBCN preceramic polymer (CF-g-GO/SiBCN). Loading of SiBCN preceramic polymer on the surface of CF-g-GO increased remarkably compared to that on the surface of untreated CFs. Pyrolysis of CF-g-GO/SiBCN preceramic polymer at 1400 °C in inert atmosphere led to the formation of SiBCN ceramics with the approximate elemental composition of Si3N4/SiC/BN. TG results show that the thermal stability of the CF with ceramic layer has improved noticeably at high temperature.

ZrB 2 –SiC coatings were prepared on the SiC coated specimens by pack cementation method at 1900 °C for 2 h. The phase, microstructure, anti-oxidation and thermal shock resistance properties of these coatings were investigated. It was found that ZrB 2 –SiC coatings improved anti-oxidation and thermal shock resistance. ZS50 coating endured 15 thermal shock cycles between 1500 °C and room temperature with 20.2% weight loss, which was attributed to the dense glass phase formed after oxidation.

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.

The ZrB2–20 vol.% SiC composites were oxidized at a constant temperature of 900 °C for 5, 30 and 60 min, respectively. Some of the oxidized specimens were immersed in water to remove the B2O3 glass from the surface in order to investigate the effect of surface microstructure and component on the flexural strength. The flexural strengths of immersed specimens are higher than original strength, but lower than those of the oxidized specimens. The increase in flexural strengths is strongly dependent on both ZrO2 and outer glassy phase. For comparison, the ZrB2–SiC composites were also oxidized at 1300 °C in air. The high oxidation temperature is detrimental to the flexural strength of composites, however, the reliability of specimen oxidized at 1300 °C is improved significantly. The effect of oxidation time was also investigated, and the flexural strength of specimens is not sensitive to oxidation time within a certain range.

To safely and reliably use aluminum nitride (AlN) helices in the fabrication of novel micro/nanodevices, it is very important to know their mechanical properties. Herein, we investigate the mechanical properties of individual AlN helices using an in situ tensile-bending test. Tensile tests reveal that an AlN helix has an average e of ~4.7 ± 0.8% elastic deformation before a typical brittle fracture occurs. The bending test shows a two-step mechanical feature—linear-elastic followed by an elastic-plastic process—with an average e bent of ~54.5 ± 0.6%. Our results provide direct cognition about the mechanical properties of AlN helices and their benefit to the design of AlN-based flexible micro/nanodevices.

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.

To improve the oxidation-resistance of carbon bonded carbon fiber composites (CBCFs), the low density and porous CBCFs modified with ZrB2 and SiC ceramics with a density of 0.26, 0.40, 0.61 and 0.77 g cm−3 were prepared by precursor infiltration and a pyrolysis method. The pyrolysis behavior of the Zr and B-containing hybrid polymeric precursor was studied. The densification behaviour was investigated through the analysis of the microstructures of CBCFs–SiC–ZrB2 (denoted as CSZ) composites with different density. The mechanical properties, thermal properties and oxidation behavior of the CSZ composites were studied. The results show that the incorporation of a ZrB2 ceramic coating does not change the anisotropic properties of the CBCF composites. The CSZ composites with a density of 0.77 g cm−3 with a continuous ZrB2 ceramic coated layer on the surface of the carbon fibers which exhibit better mechanical properties and antioxidant properties. The composites show remarkable thermal properties which are good for thermal insulation applications.

ZrB2–20 vol.%SiC ultrahigh temperature ceramic containing 5 vol.% carbon black of nanometer size (ZSC) was prepared by hot-pressing at 1900 °C. The effect of carbon black addition on the microstructure and mechanical properties was investigated. Compared to the ZrB2–SiC ceramics, the fracture toughness was significantly improved whereas flexural strength and hardness of the ZSC ceramic were slightly degraded. The fracture toughness as high as 6.6 ± 0.5 MPa m1/2 was much higher than that of monolithic ZrB2 (2.3–3.5 MPa m1/2) and ZrB2–SiC ceramics (4.0–4.5 MPa m1/2). The toughening mechanisms were the crack deflection, bridging and branching. Furthermore, the effect of carbon black addition on the thermal shock resistance was systematically investigated and discussed.

ZrB 2 –20 vol% SiC ultrahigh temperature ceramics matrix composite was hot-pressed at 1900 °C doped with the 15 vol% graphite flake (ZrB 2 –SiC–graphite). It was found that the addition of the graphite flake promoted the grain refining and densification of the ZrB 2 –SiC–graphite composite. The effect of the graphite flake orientation on microstructure and mechanical properties of the ZrB 2 –SiC–graphite composite was investigated. The results revealed the anisotropy in the flexural strength and fracture toughness of the ZrB 2 –SiC–graphite composite. In contrast to the flexural strength and fracture toughness, the hardness of the ZrB 2 –SiC–graphite composite did not show significant anisotropy.

Ablation behavior of ZrB 2 –SiC–ZrO 2 ceramics with two ZrO 2 contents was investigated using oxyacetylene torch. Thermogravimetric analysis demonstrated that ceramic with 10 vol% ZrO 2 showed initial weight change at higher temperature than the one with 20 vol% ZrO 2 . After same ablation condition, lighter oxidized microstructure and lower weight loss and line gain were obtained from ceramic with 10 vol% ZrO 2 . Ablation mechanism revealed that excessive ZrO 2 would supply much path to the inward transport of oxygen, which led to the dissatisfactory resistance to oxidation and ablation for the ceramic with 20 vol% ZrO 2 .