Bulk quantity and long-scale amorphous SiO2 nanowires have been prepared simply by direct pyrolysis of an iron-modified perhydropolysilazane (Fe-PHPS) at 1300 °C in the flowing Ar atmosphere. Scanning electronic microscope (SEM) study shows that most SiO2 nanowires
have smooth surface and they consist of straight and smoothly curved parts, with diameters in the range of 50 to 200 nm and lengths up to 200 μm. Beside this normal form of SiO2 nanowires via the typical vapor-liquid-solid (VLS) mechanism, four other different helical
forms of nanowires, named spring-shaped nanowires, twinborn nanospring, fishbone-shaped nanowires and braided-like helical SiO2 nanowires, are also observed. The formation of these nanowires is proposed to be the modulated contact angle anisotropy (CAA) mechanism based on the VLS
mechanism.
Many small-molecule Si-N-P compounds of appropriate design can function as precursors to various oligomeric and polymeric P-N systems.For example, poly(dialkylphosphazenes), (R 2 PN) n , are readily obtained via the thermal condensation-polymerization of certain N-silylphosphinimines, Μe 3 SiN=P(X)R 2 . In addition, novel 3-coordinate phosphorus-V compounds including the bis(imino)-phosphoranes, RP(=NSiΜe 3 ) 2 , can potentially lead to new polymers of formula (RPN) n , the phosphorus analogs of electrically conducting (SN) n . The synthesis of polyphosphazenes and their precursors and the synthesis of potential precursors to (RPN) n are discussed.
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