Preparation And Performances Of Carbide Nanomaterials Generated Form Plants Templates

The physical and chemical properties of carbide nanomaterials are of interest for basic research and several technological applications due to their intrinsic material properties such as high hardness, high melting point, excellent chemical stability, oxidation and corrosion resistance, excellent thermal stability, and low electrical resistivity. These properties make carbide nanomaterials very useful as cutting tools, luminescent materials, coating materials, reinforcements in composites and so on. However, there are still many problems, such as the complex synthesis methods, the unknown growth mechanisms, and the lack of basic physical parameters. In order to solve these problems, a lot of research works have been done. The main contents can be summarized as follows:(1)A generic bamboo-based carbothermal method was used to prepare NWs of both covalent carbides (SiC and B4C) and interstitial carbides (TiC, TaC, NbC, TixNb1-xC, and TaxNb1-xC). The use of natural nanoporous bamboo as both the renewable carbon source and the template for the formation of catalyst particles greatly simplifies the synthesis process. Based on the structural, morphological and elemental analysis, a volatile oxides and/or halides assisted VLS growth mechanism was proposed.(2) The unique hybrid structures consisting of TaC NWs and activated carbon microfibers can be constructed via a one-step, simple, convenient and cost effective carbothermal method using natural bamboo fibers as both the carbon source and the template. Halides were selected as both the transportation carrier of Ta and the activation agents of carbon for the simultaneous co-production of TaC NWs and activated carbon microfibers. From the measurements, we have also determined the Young’s modulus and the resistivity of individual TaC NWs, which are important parameters of these unique building blocks for practical applications. TaC NWs exhibit high Young’s modulus of375±25GPa and low electrical resistivity of62～64μΩ·cm. The unique hierarchical heterostructures of TaC/C presents excellent rate capability (>90%capacity retention at8A/g) and high capacitance (135±5F/g), with great promise for high rate electrochemical capacitive energy storage applications.(3) Single-crystalline TiC NRs on the surface of carbon microfibers were successfully synthesized via a simple, convenient, and cost-effective biotemplate method. Use of natural nanoporous cotton fibers as both the carbon source and the template for formation of catalyst particles significantly simplifies the synthesis process of TiC NRs. On the basis of the structural, morphological, and elemental analyses, a chloride-assisted VLS growth mechanism and the corresponding growth model were proposed. The activationenergy (Ea) for growth of TiC NRs was calculated to be260kJ/mol, which is similar to the Ea of bulk TiC films. From in situ AFM three-point bending measurements we determined the Young’s modulus of TiC NRs, which is an important parameter for practical applications. The measured Young’s modulus of TiC NRs ranges from390to470GPa, and the average modulus is430±22GPa. The high-modulus TiC NRs hold great promise as reinforcements for composites and as structural/functional building blocks for NEMS.(4) A simple approach to prepare NbC nanowire arrays via biotemplate method. The growth of the nanowire arrays is attributed to a VLS mechanism. Mechanical behavior of individual NbC nanowires has been probed by in situ AFM method. The measured Young’s modulus of NbC nanowires is in the range from281to453GPa, which is close to the spark plasma sintered NbC powers(296-330GPa), but lower than the theoretically predicted value of484GPa. In situ TEM probe multipoint tests revealed that the electrical resistivity of the NbC nanowire was about5.02mΩ·cm.(5) A new bamboo-based carbon thermal reduction method was used to prepare boron carbide nanoflakes. Natural bamboo powders were used as carbon source, which significantly simplify the synthesis process. On the basis of the structural, morphological, and elemental analyses, a fluoride-assisted VLS nucleation and VS growth mechanism were proposed. The resistivity of boron carbide nanoflakes was further investigated by in-situ electrical property characterization using a STM-TEM holder inside a TEM. The resistivity of boron carbide nanoflakes was calculated to be0.14MΩ·cm.(6) The feasibility to explore the correlation between the energy storage performance and the microstructure of nanostructured film was demonstrated via dynamic observation of the growth and in-situ probing the mechanical properties in aqueous electrolyte by using in-situ AFM. The pulsed current deposited porous nanostructured γ-MnO2exhibits a high specific capacitance of437F/g and a remarkable cycling performance with>96%capacitance retention after10000cycles. A series of dramatic evolutions of nanostructured MnO2film involving progressive nucleation,3D growth, reversible expansion, proton intercalation induced softening, and self-accommodation phenomena, which have not been considered in the conventional fabrication method of nanostructured MnO2, can be correlated to its remarkable energy storage performance. From the measurements, we also determined, for the first time, the Young’s modulus and nanoindentation hardness of nanostructured MnO2, which are important parameters for designing advanced electrochemical capacitors. More generally, the in-situ AFM in conjunction with in-situ nanoindentation offers great potential for addressing many fundamental issues in materials science, chemistry, mechanics, biology, and other fields of science.