Template Routes to Non-Oxide Ceramic Nano- and Micro-Structures
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0921-T04-10
Template Routes to Non-Oxide Ceramic Nano- and Micro-Structures Upal Kusari1, Zhihao Bao2, Cai Ye2, Gul Ahmad2, Kenneth H Sandhage2, and Larry G Sneddon1 1 Department of Chemistry, University of Pennsylvania, 231 S 34th Str, Philadelphia, PA, 19104 2 School of Materials Science and Engineering, Georgia Institute of Technology, 771. Ferst Drive, Atlanta, GA, 30332
ABSTRACT Efficient routes to boron carbide, boron nitride, and silicon carbide nanostructures have been developed which employ newly developed chemical precursors in conjunction with colloidal silica and biological silica “diatom” templates. Melt infiltration of the precursor into ordered silica bead templates was followed by pyrolytic ceramic conversion. Dissolution of the silica templates with HF generated highly uniform and layered, submicron-sized ceramic structures with three-dimensional periodicity and tunable length scales. Vacuum filtration of ceramic precursor solutions through bioclastic silica diatom templates generated polymer coated replicas of their 3-D nano- and micro- structures. Subsequent pyrolysis to the ceramic followed by dissolution of the frustules yielded free-standing replicas with fine features on the nanoscale. These techniques provide facile routes to nano- and micro structured non-oxide ceramic materials. INTRODUCTION The fabrication of advanced materials exhibiting well-defined and controllable nano- and micro- scale features has been of immense interest for a variety of applications in microelectronics, catalysis, sensors and gas absorbents [1]. Advanced non-oxide ceramics such as boron carbide, silicon carbide and boron nitride have a wide range of properties, including high-temperature stability and strength, large thermal conductivity, and corrosion and oxidation resistance. There has been significant interest [2-5] in generating these materials in nano- and micro-structural forms and we report here the utilization of both silica bead and diatom frustule templates in conjunction with the chemical precursors to produce boron carbide, boron nitride and silicon carbide materials on the nano- and micro- scales. EXPERIMENTAL DETAILS Colloidal silica crystals were generated using a procedure, outlined in Figure 1, similar to that reported by Colvin [6]. Monodispersed SiO2 nanospheres were produced by the hydrolysis of TEOS (tetraethylorthosilicate) in ammonical ethanol and three-dimensionally ordered, planar colloidal silica arrays with thickness ranging from one monolayer to 50 µm were then fabricated on quartz microslides by convective self-assembly of the beads during the evaporation of the ethanol solvent. The templated slide was covered with another microslide with the aid of Teflon® spacers and the microslide sandwich then placed in contact with a melt (~1 mL) of the chemical precursor in an evacuated flask. The generation of boron carbide employed a melt of the bis(decaboranyl)hexane [6,6’-(CH2)6-(B10H13)2] (BDH) precursor at 140oC [5]. The template sandwich was allowed to absorb the precursor by capillary ac
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