Nanoscaled Si-C-N-composite powders with different structures by shock-wave pyrolysis of organic precursors

Nanoscaled Si-C-N-composite powders were formed by shock-wave pyrolysis of hexamethyldisilazane (HMDS) and tetramethylsilane (TMS) with NH3-additions at temperatures of 800-2000 degrees C and reaction times in the range of 0.5 to 2 ms. The powders were analysed by FTIR, XRD, and elementary analysis. The structure, the properties, and the behaviour of the powders have proved to depend significantly on the pyrolytic conditions. In general, from HMDS by pyrolysis a real metastable-bonded complex consisting of Si-C-, Si-N-, and C-N-bonds is formed. While the powder particle-size (5 to 75 nm) and the crystalline content (<10%) are changed by the pyrolysis temperature, the stoichiometric composition can be affected by the amount of N-additions to the system. Thus, a N-content in the powder up to 28 wt.% can be achieved leading partially to an incorporation of N-atoms into the SiC lattice instead of C-atoms and a formation of a Si-C-N-network. At small NH3-additions and corresponding small N-contents in the powders noticeable crystalline SiC portions are formed. A formation of crystalline Si3N4 as well as SiC phases can be observed when the composite powders are heated up to 1400 degrees C.