T

1200oC

2 ^ +CH3NH2 TADB -CKNKC^* W-methylpolyborosilazane

Silicon boron nitride Si.B.N.

Silicon boron carbonitride

Figure 60. (a) Synthesis of the precursor molecule TADB. (b) Pyrolysis and polymerization of TADB.

aged in air at 1500 °C for 15 h, develop a crystalline oxide layer that contains several cracks and debonds from the fiber core (Fig. 61). The above example shows the advantage of molecular precursors in achieving a high degree of connectivity in the amorphous ceramic that is responsible for the unusual properties of the fibers prepared from it.

The definition of nanocomposite material encompasses a large variety of systems, such as one-dimensional, two-dimensional, three-dimensional, and amorphous materials, made of distinctly dissimilar components and mixed at the nanometer scale [337] (Scheme 29). Nanocomposites are of intense current interest for potential applications

Figure 61. Oxidation resistance of Siboramic compared with HiNicalon fibers (Nippon Carbon). (A) Fracture surface of HiNicalon fibers after exposure to air (15 h, 1500 °C). (B) Fracture surface of SiBN3C fibers after exposure to air (50 h, 1500 °C). Reprinted with permission from [616], P. Baldus et al., Science 285, 699 (1999). © 1999, American Association for the Advancement of Science.

Figure 61. Oxidation resistance of Siboramic compared with HiNicalon fibers (Nippon Carbon). (A) Fracture surface of HiNicalon fibers after exposure to air (15 h, 1500 °C). (B) Fracture surface of SiBN3C fibers after exposure to air (50 h, 1500 °C). Reprinted with permission from [616], P. Baldus et al., Science 285, 699 (1999). © 1999, American Association for the Advancement of Science.

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