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The kinetics of the CVD of boron nitride from trimethoxyborane (TMOB) and ammonia (NH 3 ) under atmospheric pressure was investigated by varying the following process parameters: temperature, residence time of the reactants, molar fraction of TMOB, and the NH 3 /TMOB ratio, c. A kinetic power law equation was derived, that describes the experimental results with good accuracy. The reaction order with respect to TMOB is found to be 0.9 and ± 0.2 with respect to NH 3 . Between 800 C and 950 C, the deposition rate is controlled by the surface reaction kinetics with apparent activation energy of 115.1 kJ mol ±1 . The deposited BN films were characterized by IR spectroscopy, Raman spectroscopy, and X-ray diffraction (XRD). The microstructure of the deposits depends on the nature of the substrates used. Turbostratic boron nitride (t-BN) was deposited on graphite, and hexagonal boron nitride (h-BN) on alumina substrates. X-ray photoelectron spectroscopy (XPS) analyses show nearly stoichiometric BN films for deposition temperatures in the range 850±950 C for high amounts of ammonia (100 < c < 150) in the feed gas.

Carbon short fibers (6000 filaments) with a length of 6 mm were uniformly coated with pyrolytic carbon (pyC) in continuous CVD process using propane-hydrogen mixture as precursor. The process conditions for the fiber coating were optimized to meet a high deposition rate at minimum soot formation in parameter screening experiments using nonporous graphite substrates. The coated fibers were characterized by SEM and Raman spectroscopy. Their reinforcing effect was investigated in composites with C/SiC matrix. As a result of fiber coating the bending strength of the composites was increased about 30% and elongation at break increased by a factor of nine. The pyC coating modifies the fiber-matrix interface preventing too strong a bonding, resulting in damage tolerant behavior of the composites.