Nonoxide precursor route

The purpose of this chapter is to provide an overview of the chemistry, processing and application of boron-containing preceramic polymers in the BN system. The nonoxide precursor route, also called the Polymer Derived Ceramics (PDCs) route, represents a chemical approach based on the use of air- and/or moisture-sensitive (molecular or polymeric) precursors by means of standard Schlenk techniques and vacuum/argon lines. This precursor route allows the chemistry (e.g., elemental composition, compositional homogeneity and atomic architecture) of molecular precursors to be controlled and tailored in order to provide the ensuing preceramic polymers... 

Fiber preparation via the polymer precursor route provides many desirable properties for use in continuous-fiber ceramic matrix composites intended for high-temperature uses in oxidative and nonoxidative environments [65]. These fibers, especially those having low electrical conductivity and good dielectric properties, are being investigated for use in radiation-transparent structures, such as radomes [66]. 

Fabrication routes in which a solution of metal compounds is converted into a solid body are sometimes referred to as liquid precursor methods. The sol-gel process has attracted considerable interest since the mid-1970s and forms the most important liquid precursor route for the production of simple or complex oxides. The pyrolysis of suitable polymers to produce ceramics (mainly nonoxides such as SiC and Si3N4) has attracted a fair degree of interest in the past 20 years. It is an important route for the production of SiC fibers. 

Gas-phase reactions for the formation of nonoxide powders have been known for a long time. In the last few years many of these routes were reinvestigated and other precursors have been developed. This is mainly because of their potential to yield very fine grained nonoxides, with mean grain sizes in the nanometer range. Routes via the gas phase have also been intensively studied for the direct formation of coatings that is, CVD (chemical vapor deposition). All reaction paths basically considered as a CVD process can be tailored for the formation of powders the processing parameters must be optimized. 

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