Synthesis of nanoscale materials via a novel chemical vapor deposition based apparatus.

摘要

Nanoscale materials are of interest due to the unusual properties afforded by their size. Two such morphologies, nanoparticles and the recently discovered “nanobelt” materials, are explored in this thesis.; A novel nanoscale material synthesis apparatus was constructed. It consists of four primary components: an evaporation chamber, a chemical vapor deposition furnace, a collection chamber, and a powder reservoir. A two-stage subsonic jet separates the first two components, permitting nanoparticle production to occur independently of subsequent chemical and thermal treatment.; An experimental design was conducted to examine the roles of several variables during the formation of graphite-encapsulated nickel nanoparticles. Coating morphology was strongly dependent on furnace temperature, which exhibited a more subtle influence on mean particle size. The percentage of nickel surviving acid treatment depended primarily on hydrocarbon identity, as well as furnace temperature and carbon atom flux. Acetylene at high temperature yielded crystalline carbon coatings and the greatest percentage of protected nickel achieved, but with an excess of carbon in the product.; Additional encapsulated nickel experiments were conducted with reduced acetylene flowrates and a staggered furnace temperature. Thermogravimetric analysis of the as-collected powder revealed that the coating was a crystalline and amorphous carbon hybrid. While this coating effectively protected large clumps of embedded nickel, removal of the amorphous carbon by oxidation rendered individual particles susceptible to hydrochloric acid attack.; Amorphous silica was introduced as an alternative coating material via tetraethoxysilane decomposition. Transmission electron microscopy confirmed the production of well-dispersed, acid-resistant particles with a nickel core and silica shell.; The synthesis of nanoscale alumina heterogeneous catalyst substrates was investigated. Exposure of aluminum nanoparticles to large amounts of air or oxygen in the CVD furnace yielded a partially oxidized or amorphous ceramic product. Crystalline alumina was formed by introducing oxygen directly into the arc environment. A graphite cathode was found to significantly reduce impurity generation compared to tungsten cathode use. X-ray diffraction identified delta alumina as the majority phase.; The production of nanobelt materials was explored. A vapor-liquid-solid formation mechanism was proposed for tin oxide nanobelts, while magnesium oxide nanobelts and various derivatives were grown by an apparent vapor-solid mechanism.