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  • 1
    Electronic Resource
    Electronic Resource
    Kinetic Investigation of the Curing and Pyrolysis Procedures Used for the Preparation of Polymer-Derived Boron Nitride Fibres (2006)
    s.l. ; Stafa-Zurich, Switzerland
    Advances in science and technology Vol. 45 (Oct. 2006), p. 726-734 
    Details
    ISSN: 1662-0356
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: The kinetic investigation of the solid-state decomposition of a typical melt-spinnablepoly[B-(methylamino)borazine] into boron nitride fibers was carried out at various heating rates. Itwas shown that the two-step weight loss associated with the polymer-to-ceramic conversion isgoverned by two major diffusion-type transport mechanisms which are independent of the appliedheating schedule. The application of the Kissinger and Friedman methods to dynamic TG dataallowed us to measure the Ea and lnA values which are seen to increase with the extent of theceramic conversion from region one (Ea=46.3kJ/mol, lnA=3.85; Friedman method) in going toregion two (Ea=122.6J/mol, lnA=12.18; Friedman method). Kissinger and Friedman results are ingood agreement. It was shown that the cross-linking process of the polymer is mainly governed by apoorly energetic mechanism indicating the occurrence of simple reactions, whereas themineralization and ceramization steps are majoritarly represented by a highly energetic mechanismsuggesting the occurrence of complex and multi-step mechanisms
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/01/42/transtech_doi~10.4028%252Fwww.scientific.net%252FAST.45.726.pdf
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  • 2
    Electronic Resource
    Electronic Resource
    A New Generation of Boron-Based Ceramic Fibers: Design, Processing and Properties of SilicoBoron CarboNitride (SiBCN) Fibers from Boron-Modified Polyvinylsilazanes (2006)
    s.l. ; Stafa-Zurich, Switzerland
    Advances in science and technology Vol. 50 (Oct. 2006), p. 9-16 
    Details
    ISSN: 1662-0356
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Natural Sciences in General , Technology
    Notes: Boron-modified polyvinylsilazanes have been studied for suitability as fiber precursor. Amelt-tractable polymer displaying Si- and N-bonded methyl groups was successfully processed intogreen fibers ~18μm in diameter via a melt-spinning process. After the shaping process, the use ofan ammonia curing atmosphere at 200°C allowed to increase the ceramic yield of the polymer, thenavoid inter-fiber fusion during the further increase of the temperature. As-cured fibers wereannealed in the temperature range 1000-1800°C in a nitrogen atmosphere to provide SiBCNceramic fibers black colored, of flexible form and ~12μm in diameter in different crystallinity statesgoing from totally amorphous below 1600°C to well-crystallized at 1800°C. The excellent strengthretention after heat-treatment at 1600°C (1.3-1.5GPa) is clearly related to the high amorphousstability of fibers. Elemental compositions of such amorphous fibers showed a typical chemicalformula of Si3.0B1.0C5.0N2.4. Between 1600°C and 1700°C, the fiber strength decreased to 0.9GPathen dropped to about one-quarter the original value at 1800°C while structural changes wereevident by XRD analysis
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/01/42/transtech_doi~10.4028%252Fwww.scientific.net%252FAST.50.9.pdf
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  • 3
    Electronic Resource
    Electronic Resource
    Dots Formation by CVD in the SiC-Si Hetero-System (2008)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 600-603 (Sept. 2008), p. 571-574 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The formation of dots by CVD in the hetero-system SiC-Si was studied in the twopossible ways : Si dots on SiC substrate and SiC dots on Si substrate. The substrates underwentspecial surface treatment to reveal a network of parallel steps before deposition of the dots. In the Sion SiC case, the dots density on the 8°off 4H-SiC substrate varied in the range 107 – 7x108 cm-2 andmainly depends on the SiH4 flux and the deposition time. The Si dots are in majority aligned alongthe step edges of the substrate. In the other hetero-system, only propane was introduced in thereactor to performed a localised carbonisation of the Si(111) 1.5°off substrate. The SiC dotsobtained at 1200°C have similar density the Si ones but with smaller size
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/20/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.600-603.571.pdf
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  • 4
    Electronic Resource
    Electronic Resource
    Crystallinity, Crystalline Quality, and Microstructural Ordering in Boron Nitride Fibers (2005)
    Oxford, UK : Blackwell Science Inc
    Journal of the American Ceramic Society 88 (2005), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A qualitative and quantitative analysis of the microtexture/microstructure in several experimental boron nitride fibers was investigated by X-ray diffraction and electron microscopy according to their mechanical properties. Young's modulus was controlled by grain orientation. The disordered microstructure of low modulus fibers consisted of amorphous regions and nanometer-sized crystallites arranged in a wide range of orientation. In contrast, high modulus samples showed a coarse-grained microtexture in which crystallites were ordered in a meso-hexagonal arrangement along the fiber-axis. Cracks were easily propagated as crystallinity increased, leading to decreased failure strain. The strength-microstructure relationship was obscured by the fiber porosity and defects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2005.00318.x
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