SiC fibers with electrical resistivity of different orders of magnitude are of great interest for the fabrication of advanced composites with electromagnetic wave absorbent performance as both structural and functional materials. KD-S and KD-SA fiber produced by National University of Defense Technology were oxidized at 800°C air to get KD-OS and KD-OSA respectively. The microstructure and electrical resistivity of near-stoichiometric SiC fibers (KD-S, KD-OS, KD-SA, KD-OSA) were analyzed and evaluated in detail. The SiC fibers consisted of β-SiC nanocrystallines and free carbon. Apart from KD-OSA, these SiC fibers exhibited a uniquely specific skin-core structure with thin carbon-rich layer of about 25 nm on their surfaces. So the electrical resistivity of KD-OSA was 2961.7Ωcm which was much higher than the rest of the fibers. After testing the porosity and pore size distribution of the fibers, we discover that the pore structure of KD-SA is more abundant than that of KD-S and KD-OS to the extent that the resistivity of KD-SA is higher than that of KD-S and KD-OS.

激光驱动惯性约束聚变有望解决能源危机,但聚变过程条件的苛刻性对在其中充当靶丸材料的空心微球的品质,如球形度、壁厚均匀性、表面粗糙度、壳层材料密度等提出了严格要求,而制备方法的选择及条件控制直接影响到微球的上述性能.本工作主要综述了研究较为广泛的炉内成球技术、降解芯轴技术以及乳液法的制备过程、适用范围、优劣势等,并对乳液法的形成机理和影响因素进行了较详细的阐释.

The energy is the material basis to support the whole process of human civilization, and it is also an integral part of modern social development basic condition. Wind, solar, tidal power, geothermal energy, and other all belonging to renewable clean energy will become the main energy source in the future. However, renewable energy generally has a large amount, low energy density, randomness, and intermittent, which cause it hard to use. In this situation, the development of efficient energy storage to meet human demand for energy is to become a hot spot in the worldwide. Electrochemical energy storage of high efficiency and low investment and the use of safe, flexible application characteristics have attracted people for the further research of this kind of energy storage methods. And lithium-ion batteries and battery as nowadays most rapid development, the paper first summarizes the development status of the existing lithium-ion battery. Then proposes a kind of by large algae biomass—Enteromorpha as precursor system of lithium-ion battery cathode materials and assemble them into analog battery. At last, the electrochemical properties and physical structure have been characterized in the paper.

The precursor-derived and near-stoichiometric SiC fibres (KD-S) were exposed at 1000–1500°C for 1 h in the simulated aeroengine circumstance of PH2O:O2:Ar = 14:8:78 KPa with the gas rate of 200 ml/min. The results indicated that the oxidized KD-S fibres were covered by silica layer. The oxygen content, grain size of silica, and oxide layer thickness increased, whereas the tensile strength decreased with rising annealing temperature. KD-S fibres treated under simulated aeroengine circumstances showed larger SiO2 grain size, thicker silica layer, and better residual strength than those annealed in dry air. The steam could accelerate the oxidation on KD-S fibres by reducing the active energy. The influence of water vapour on the oxidation behavior of KD-S SiC fibres was investigated and discussed as well.

Si-C-O ceramic fibers were prepared from commercial silicon resin by means of melt spinning, UV curing and pyrolysis. The composition and structure of the precursors were characterized with FT-IR and NMR. Silicon resin exhibited excellent spinning performance for use as a precursor to prepare continuous fibers. UV irradiation was employed to complete the cross-linking of the green fibers, and the mechanism of the curing process was determined with FT-IR. After pyrolysis at 1 000 degrees C, Si-C-O ceramic fibers were obtained, which exhibited good flexibility with 7.5 mu m in diameter and 0.8 GPa in tensile strength. The obtained fibers remained amorphous below 1 300 degrees C. When the temperature reached above 1 300 degrees C, SiC with a small crystal size appeared because of carbothermal reduction, and the fiber gradually lost mechanical strength owing to the pores caused by release of low-molecular-weight molecules such as CO, CO2 and SiO.

Silicon nitride (Si3N4) nanowires were synthesised using H-2-treated SiC fibres as raw materials and a graphite cylinder as the substrate at 1500 degrees C in N-2 atmosphere. The nanowires were characterised by X-ray photoelectron spectroscopy, chemical analysis, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The results showed that the Si3N4 nanowires have diameters ranging from a few tens to hundreds of nanometres and lengths of several hundred micrometres. The preferred growth direction of the nanowires was (010), and the nanowires comprised single-crystalline alpha-Si3N4. In addition, the formation mechanism of Si3N4 nanowires was discussed. The free silicon in the H-2-treated SiC fibres was found to react with N-2 to form Si3N4 nanowires, leading us to speculate that the growth mechanism involves a vapour-solid process.

The low oxygen content SiC fibers were exposed in simulated aeroengine circumstance of 14 kPa kPa kPa at 1200 ℃ for 1-50 h. Performances and structure of the fibers were characterized by element analysis, XRD, SEM and tensile test. The results show that the fibers have higher oxygen content, thicker oxide layer, lower strength compared with the fibers treated in dry air. Cracks and α-SiO2 crystal are more likely to occur in silica layer. The steam in the simulated circumstance can accelerate oxidation and crack formation in silica film.

As by-products produced by the synthesis of polycarbosilane, RLPS and dimethyldivinylsilane (DVS) can synthesise vinyl-containing liquid polycarbosilane (LPVCS) via hydrosilylation reaction. The structure, thermal curing performance and pyrolysis performance of PVCS are characterised by means of the analysis means such as FT-IR, GPC and TG, etc. According to the result, the structure of PVCS is affected by the different synthesised temperatures and different proportions of introduced DVS. And LPVCS that contains Si-H and -CH=CH2 groups is synthesised under the control of reaction condition. Cross-linking solidity is available at 350 degrees C in an inert atmosphere, and the total ceramic yield of LPVCS is 42.5%. The oxygen content of the pyrolysed product is just about 2.0% after heating in 1000 degrees C, which is a suitable precursor polymer for SiC-based composite.

Due to the extensive applications of SiC fiber-reinforced composite materials in the fields of aviation, aerospace, and nuclear power, there are increasing demands for SiC fibers with both excellent mechanical performance and high-temperature stability. In this work, nearly stoichiometric polycrystalline SiC fibers were fabricated using amorphous Si-C-Al-O fibers with excess carbon and oxygen (C/Si = 1.34, O content: 7.74 wt%). The nearly stoichiometric composition (C/Si = 1.05) of the product fibers was achieved by thermal decomposition of the starting fibers. The fibers were well-crystallized with grain sizes of similar to 200 nm due to sintering at a high temperature of 1900 degrees C. The fibers exhibited a high tensile strength and a high elastic modulus and were composed of SiC grains with twins and stacking-faults, exhibiting intragranular fracture behavior. Furthermore, the fibers maintained their original tensile strength after being maintained at 1800 degrees C for 5 hour or at 1900 degrees C for 1 hour under an inert atmosphere, and they exhibited a high strength retention (97%) after exposure at 1300 degrees C for 1 hour under air. The high-temperature stability and creep resistance of the fibers were comparable to that of commercial Hi-Nicalon S and Tyranno SA fibers.

Three dimensional and four directional carbon fiber reinforced SiC matrix (C-f/SiC) composites were fabricated by precursor infiltration and pyrolysis process employing a new precursor, liquid polyvinylcarbosilane (LPVCS). LPVCS is a novel precursor with active Si-H and -CH=CH2 groups with relatively high oxygen content (similar to 7.3 wt%). The mechanical properties improvement caused by ameliorated interface and low porosity was researched. Samples with ameliorated interface employing LPVCS show better mechanical properties than those employing polycarbosilane (PCS). The flexural strength and fracture toughness of the C f /SiC composites fabricated with PCS are 301 MPa and 11.2 MPa.m(1/2), respectively, whereas those of the samples fabricated with ameliorated interface are 442 MPa and 26.1 MPa.m(1/2), respectively. Employing LPVCS for the first infiltration and pyrolysis cycle forms suitable interface, employing PCS as precursor for the left several cycles forms relatively low oxygen content matrix, and then employing LPVCS for the last several cycles forms low porosity, which is the main reason of mechanical properties improvement.

The polycarbosilane-derived KD-II SiC fibers were exposed in air at 1200°C for 1-100h and the effect of heat treatment on structures and properties were studied by elemental analysis, XRD, SEM and tensile test. Experimental results indicated that oxygen content, grain size of SiO2 and oxide layer thickness increased, whereas the tensile strength decreased with rising the heat treatment time. When oxidizing over 20h, the amorphous silica crystallized into α-cristobalite and there were cracks on fibers surface and the cross section formed the skin-core structure with oxide layer wrapped inner SiC fibers after oxidizing for 100h. With the same experimental condition for Hi-Nicalon SiC fibers, the differences of oxidation resistance between KD-II and Hi-Nicalon SiC fibers were compared and the oxidation degradation of KD-II SiC fibers was analyzed.

Boron carbide is one of the most widely used non-oxide ceramics as it possesses excellent physical and chemical properties. Much attention has been paid to prepare boron carbide ceramics via precursor derived method. In this work, poly(6-norbornenyldecaborane)-b-poly(6-cyclooctenyldecaborane) (PND-b-PCD) block copolymer was synthesized by the ruthenium-catalyzed ring-opening metathesis polymerization (ROMP) of 6-norbornenyldecaborane with 6-cyclooctenyldecaborane. The synthesized boron carbide preceramic polymer had good solubility and film-forming ability with a high ceramic yield of 75% at 850 °C. TGA, XRD and TG-IR-GC–MS were used to investigate the ceramization process of the precursor. Boron carbide ceramic foams were prepared by the precursor via replicating polyurethane foam template. The component, crystalline and morphology were investigated in detail. The ceramic foams showed a good high temperature performance and could keep their structure even up to 1800 °C.

Three dimensional and four directional carbon fiber reinforced SiC matrix (C-f/SiC) composites were fabricated by precursor infiltration and pyrolysis process with ameliorated interface employing a new precursor, liquid polyvinylcarbosilane (LPVCS). LPVCS is a novel precursor with active Si-H and -CH=CH2 groups with relatively high oxygen content (similar to 7.3wt. %). The mechanical properties improvement led by ameliorated interface was researched. Samples with ameliorated interface employing LPVCS showed better mechanical properties than those employing ploycarbpsilane (PCS). The flexural strength and fracture toughness of the C-f/SiC composites fabricated with PCS were 301 MPa and 11.2 MPa.m(1/2), respectively, whereas the equivalent values of the samples fabricated with ameliorated interface were 421 MPa and 25.6 MPa.m(1/2) , respectively. Employing LPVCS for the first infiltration and pyrolysis cycle formed suitable interface, then employing PCS as precursor for the left cycles formed relatively low oxygen content matrix, this the main reason of mechanical properties improvement.

A precursor-derived SiC fiber with low oxygen content ( KD-II) was treated respectively at 1400℃, 1600℃, 1800℃ and 2000℃ for 1 hour in flow argon. The residual strength and microstructures were characterized by XRD and SEM analysis. Results showed that with the temperature increased, the crystal size and porosity ofβ-SiC in fibers increased while the tensile strength decreased. The strength of fiber could remain over 1 GPa after heat treatment at 1800℃. The strength decrease of the fiber was caused by the growth of β-SiC crystal, decomposition of SiCxOy phase and the increase of the free carbon.

Due to their fantastic mechanical and high-temperature resistant properties, SiC fibers with electrical resistivity of different orders of magnitude are of great interest for the fabrication of advanced composites with electromagnetic wave absorbent performance as both structural and functional materials. On the basis of well-developed route to prepare SiC fibers, in this work, we demonstrated a facile strategy to fabricate SiC fibers with electrical resistivity of 10−1–106Ωcm by simply employing hydrogen and ammonia as the reactive atmospheres. The SiC fibers with different electrical resistivity had favorable morphologies, with uniform elemental distribution and stable C/Si ratio towards the fiber interior. Moreover, these fibers exhibited excellent mechanical strength and high temperature performance. Due to the innovative strategy, convenient operation and scalable preparation, the method in this work can be further extended to prepare SiC base fibers with adjustable electrical resistivity from other precursors.

SiC fibers have been intensively developed for application in advanced aerojet engines, stationary gas turbines and nuclear reactors of the future. In this work, SiC fibers with controllable carbon-rich layer were prepared by sintering under vacuum, which could be attributed to the release of gaseous silicon under vacuum at high temperature. The thickness of the carbon-rich layer on the fiber surface could be adjusted by changing the sintering temperature. Moreover, the carbon-rich layer was well distributed on the fiber surface, combining closely with the interior of the fiber. The as-prepared SiC fibers had high tensile strength and relatively low elastic modulus, which was favorable for weaving into different fabrics. Furthermore, the fibers also exhibited excellent ultra-high temperature resistance due to the presence of carbon-rich layer on the surface, which was better than that of the Hi-Nicalon and Hi-Nicalon S fibers.

Polycarborane, as a kind of boron carbide polymeric precursor, was synthesized by hydroboration reaction with styrene, divinylbenzene as the carbon resource and borane as the boron resource in this work. The polymer precursor which had good solubility and film-forming ability was soluble in most organic solvents. Furthermore, polycarborane was used to fabricate hollow polymer microspheres by emulsion technique. The compact boron carbide ceramic hollow microspheres were prepared by ceramization of the polymer microspheres. Ceramic microspheres with diameters ranging from 1 to 1.5 mm and shell thicknesses from 15 to 30 μm were easily prepared by changing emulsion composition and curing conditions. Micrographs of SEM showed that the hollow microspheres had smooth surface and good sphericity. These boron carbide ceramic hollow microspheres are of significant importance for application in the field of neutron moderator in nuclear reactors, power generation in deep space flight, etc.

A brand-new way to diverse Zr/Si/C/O preceramic polymers from dilithiozirconocene complex and chlorosilanes was designed for the first time. This simple route was fulfilled in normal pressure and at room temperature, without heating, cooling, pressurizing or electrolyzing. The pyrolysis of polymers and crystallization of polymer-derived Zr/Si/C/O ceramics were investigated by a combinational characterization of TGA, XRD, TG-FTIR, TG-GC-MS, SEM and EDS. By such polymers, Zr/Si/C/O ceramic foams with 3D networks were obtained at 1000°C. The specific surface area of such ceramic foams was 78.18m2/g, while the pure skeleton density and geometrical density were as low as 1.66 and 0.056g/cm3. Interestingly, such ceramic foam showed fair thermal stability, whose cellular structure and mesoporous microstructure could maintain from 1000°C to 1800°C. Also, such non-ferrous materials performed attractive wave-absorbing properties at tunable frequencies from 15GHz to 4GHz, with maximum reflection loss of −39dB (1000°C) and −37dB (1800°C). These lightweight mesoporous Zr/Si/C/O ceramic foams with wave-absorbing and heat-resisting properties are promising candidates for high-temperature absorbents.