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Because of low cost, low toxicity and simple synthesis method, transition metal oxides have been regarding as promising candidate materials for sodium ion batteries (SIB). In this work, O3-type layered oxide of Na0.9Ni0.45Ti0.55O2 was synthesized and evaluated as a novel bipolar material for SIB. It is found that, as a cathode material, the initial discharge capacity can reach around 109.6 mAh g−1 at 0.05C. When severing as anode material, it displays a reversible capacity of 44.5 mAh g−1. The bipolar character is attributed to two different redox active substances in Na0.9Ni0.45Ti0.55O2 with the high-voltage redox couple Ni4+/Ni2+ and the low-voltage redox couple Ti4+/Ti3+. This study provides new insights into the design and synthesis of novel electrode materials for SIBs and some other applications.

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 ...

(Gadolinium) Gd-doped antiperovskite compounds Mn 3 Cu 1−x Gd x N were synthesized by the conventional solid-state reaction. With increasing Gd concentration, two magnetic transitions appeared at a high Curie temperature (T C1 ) corresponding to paramagnetic (PM)-ferromagnetic (FM) transition and a low temperature (T C2 ) ascribed to the FM-antiferromagnetic (AFM) transition. The magnetic relaxation results show the formation of a magnetic metastable state after the FM-AFM transition at low temperature (lower than T C2 ), forming a novel magnetic-step feature in the process from AFM to FM under a certain magnetic field.

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.

Polycrystalline ZrB2 coating was prepared on graphite by chemical vapor deposition (CVD) using a gas mixture of ZrCl4, BCl3, H2, and Ar at 1200 °C. The microstructure and phase composition of the coating were investigated. The results indicated that the coating structure was loose. ZrO2 and B2O3 detected on the surface of ZrB2 grains were formed by oxidation due to exposure to air. Some adsorbed oxygen, nitrogen, and water vapor was also detected on the surface of ZrB2 grains. The feasibility of preparation of ZrB2 on graphite by CVD using ZrCl4, BCl3, and H2 was verified.

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.

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.