Design, structure and properties of organomorphic composites as new materials

Abstract

Reinforcing basis of high-temperature composite materials conventionally consists of derivatives of multifilament fibers: fabrics, rods, plaited yarns, etc. Another example of an appropriate preform is a biomorphic preform (BP) obtained by pyrolysis of wood. On the one hand, organomorphic preforms (OP) are prepared based on filaments of organic precursors of carbon, silicon carbide, and carbonitride fibers – polyacrylonitrile, polycarbosilane, and polysilazane, respectively. On the other hand, nonoxidizing pyrolysis of densified bundles of such fibers is used as in the case of BP. Autohesion interaction occurring upon contact of compressed polymer filaments during the initial stage of pyrolysis inherits at compression kept up to OP transition into inorganic state. As a result, uniform dense (0.4–0.5 of ρfiber) strong preforms are formed with narrow and very small equivalent diameter of pores: from few to 30–40 µm. Reinforcement in preforms can be uni-, bi- or three-directional. Subsequent densification of OP by vapor or liquid phase methods allows obtaining organomorphic composites (OC) with improved properties, some of which (gas permeability, surface roughness, capability of making articles with thickness of no more than 0.3 mm) are unattainable for existing high-temperature structural composites.