CHEMICAL FORMATION OF CERAMICS

Technical non-oxide ceramic materials are fabricated according to conv entional powder processing methods, which involves heat-treatment at t emperatures up to 1700-2100 degrees C and addition of metal oxides for the purpose of enhanced densification. Since the investigations of Ve rbeek et al. and Yajima ed al. in the mid-1970s, a new method has been available to produce advanced ceramics at significantly lower tempera tures (800-1500 degrees C) by the polymer pyrolysis of appropriate org anometallic precursors. The work presented in this paper focuses on th e synthesis and characterization of advanced ceramic fibres, bulk mate rials and powders based on the binary, ternary and quaternary systems Si-N, Si-C-N and Si-E-C-N. Herein E refers to B, Al, Ti, P or Zr. In p articular, the cross-linking and pyrolysis behaviour of polysilazanes, polysilanes and poly-silylcarbodiimides has been analysed by chemical analysis, FTIR, TGA, XRD, analytical TEM and mass spectrometry. Addit ionally, the crystallization behaviour of the pyrolysed amorphous inte rmediates into multiphase ceramic materials has been characterized. Si nce the partitioning of boron containing ternary and quaternary system s has been shifted to extraordinarily high temperatures (1700 degrees C), a novel class of metastable, amorphous high-temperature materials could be generated, which is not available using conventional techniqu es. The study of the oxidation behaviour of dense polysilazane derived Si-C-N bulk materials revealed corrosion resistance in pure oxygen up to 1600 degrees C.