Preparation, Activation And Polymer Composites Of Boron Nitride Nanotubes

There has been much recent interest in boron nitride nanotubes(BNNTs) for their electronic,thermal,and mechanical properties,which are in many cases different from and/or superior to those of carbon nanotubes.For example,BNNTs are semiconductors with a wide band-gap(5.5 eV) independent of the nanotube chirality or morphology.The thermal conductivity,oxidation resistivity,thermal and chemical stability,and yield resistance of BNNTs are higher than those of their carbon analogs. Therefore BNNTs are thought to be primarily useful in nanoseale semiconductors working in oxidative or hazardous environments at high temperatures,and as additives in composites that lead to improvement of mechanical properties and thermal conductivity of the matrix.In this dissertation,my research focuses on three fields including:(1) the synthesis of BNNTs via carbon nanotubes substitution;(2) activation of the chemically inert BNNTs;(3) fabrication of nanocomposites using activated BNNTs.Major results are summarized as follows.Chapter 1:The syntheses,physical properties,challenging application and recent development of BNNTs are briefly reviewed,and the research purpose and detailed plan are clarified.Charter 2:BNNTs were produced by carbon nanotubes substitution using boric acid and ammonia as reactants.The products were confirmed by a variety of characterization techniques such as Fourier-trans-formed infrared(FT-IR),X-ray diffraction(XRD),X-ray photoelectron spectra(XPS),thermogravimetric analysis (TGA),scanning electron microscopy(SEM),transmission electron microscopy (TEM).The yield and morphology of BNNTs are suggested to be affected by the ratio of materials,position of the reactants in the reactor,ammonia flow and temperature.A detailed growth model is also suggested for the carbon nanotubes substitution reaction.Chapter 3:The activation methodology is based on the chemical reaction between the isocyanate group and the amino group on the BNNTs.The activated BNNTs were further reacted with acid,amine and alcohol,and the products featuring with the formation of covalent bond with proton chemicals were characterized by FT-IR,XPS and TGA.Charter 4:On the basis of the polymer(poly(vinyl alcohol)(PVA) and Hydroxypropyl Methylcellulose(HPMC)) functionalized BNNTs,two novel polymer-BNNTs composites were fabricated.BNNTs disperse well in the polymer matrix,and improve the homogeneity of the composite films.As a result,the mechanical properties of the polymers have been improved as reflected in the Young's modulus and strength.This indicates that with strong covalent bonding,the functionalized nanotubes could offer extra benefits to increase the Young's modulus and the tensile strength for nanocomposites.As increasing of the loading of activated nanotubes,mechanical properties can be further improved.Chapter 5:Our researches in fullerene include:(1) try to synthesize bowl-shaped compound using cyclopentanone as starting materials;(2) try to synthesize cage compound C₂₄Cl₁₂.Our first approach to the target compound is the pyrolysis of C)8Cl₁₀,a compound containing fused pentagons.The second approach is the condensation of three cyclic ketone monomer(C₈H₁₀O) with fused pentagons.Deeper studies are necessary for the synthesis of smaller fuUerenes.(3) The crystals of C₅₀Cl₁₀ were obtained by evaporation of toluene solution.The structure was solved and refined in the anisotropic approximation using SHELTXL,showing the existence of the fused pentagons and the aromaticity of the sp²-hybridized carbon framework of C₂₀.