Synthesis And Characterization Of Boron-based Norganic Non-Metallic Nanomaterials

Nanopartiele materials are a new class of advanced materials exhibitingunique chemical and physical properties compared to those of their bulkmaterials. They would be potentially found applications in many fileds, suchas electronics, energy, chemical, medication and so on. So Nanopartielematerials have been widely studied all over the world.As a novel nano-material, boron nitride nanotubes （BNNTs） have beenpredicted to exhibit many better properties compared to carbon nanotubes.But large-scale and high-purity production of BNNTs hasn’t been achievedin the last two decades. Unquestionably, this problem hinders thedevelopment of their optical applications. Inorganic boron-containingcompounds, such as boron carbide, are one of the most important groups forapplication in high-temperature performance, electronics and catalysts.Traditionally, they were prepared by high-temperature reaction, but theproducts were beyond nanometer scale.In this dissertation, a comprehensive investigation of literatures aboutthe applications and syntheses of BNNTs and inorganic boron-containingcompounds was conducted. Based on that, some new synthesis techniquesor routes were developed to prepare them. Large scale preparation ofbamboo-like and cylinder BNNTs have been carried out successfully viaself-propagation high-temperature synthesis and chemical vapor depositionsynthesis （SHS-CVD）. Single phase of boron carbide ultrafine powders, aswell as α-boron nanopowders and TiC, was synthesized by a fast-pyrolysisSHS method. In addition, bulk hexagonal boron nitride has beencontinuously synthesized under flowing nitrogen atmosphere at1800-1950°C in an intermediate frequency furnace. More detailed asfollows:1. Bamboo-like and cylinder BNNTs were synthesized at1050¹150°C by SHS-CVD method using the catalytic boron-containing porousprecursors B₂7Co₈（MgO）₂1and B₁8Ca₂（MgO）₉, respectively. The productswere characterized by SEM, TEM, HRTEM, XRD, FT-IR and Ramanspectroscopy. The purities of BNNTs were estimated more than85wt%.Four growth models, including tip, base, based tip and base-tip growthmodels, were proposed based on the catalytic VLS growth mechanism forexplaining the formation of the as-synthesized BNNTs. Chemical reactionsand annealing mechanism were also discussed.2. high-purity single phase of boron carbide ultrafine powders wassynthesized from the B2O3, Mg and sucrose （C₁2H₂2O₁1） via afast-pyrolysis-SHS method. The particle size is ranging from50to200nm,with approximately90nm in average. During the fast-pyrolysis-SHS, largeamount of inert vapor of H₂O and CO gases were also released which bringa great benefit for forming uniform ultrafine B₁3C₂grains, because it can notonly reduce the temperature for preventing aggregation, but also play animportant role in isolating the crystalline particles to form homogeneouslyfine powders. Meanwhile, the α-boron nanopowders and TiC were alsosynthesized by the same methord.3. Bulk hexagonal boron nitride （h-BN） has been continuouslysynthesized from C₃N₆H₆and H₃BO₃under flowing nitrogen atmosphere at1800¹950°C in an intermediate frequency furnace. The high yield of h-BNwas up to98.54%. The products were pure h-BN flakes with diametersbetween0.5to5μm and an average thickness of about250nm. This is aninexpensive and feasible technology suitable for industrial scale production.