Stabilization of Acrylic Fibers and Microstructure of Carbon-Carbon Composites

摘要

The work on the stabilization of acrylic fibers has demonstrated that various mantle-core structures are observed at intermediate stages of stabilization, that the dark mantles seen in optical thin sections can be related to the etched mantles seen on exposure to solvents for PAN, that the mantles seen on fractured fiber ends reflect the underlying structure of the partly-stabilized fibers, that the development of these various mantless with time depends on the nature of the precursor fibers and the processing conditions, that liquid droplets can be produced during fracture of fibers during stabilization, and that the fracture of even a small number of fibers can produce effective cementation of a yarn during processing. The study of the interaction between mesophase material and carbon fibers has directed attention to the precipitation, growth and coalescence of mesophase material, which processes require ordering of small molecules in a viscous medium. On this basis, dynamic motion in the fluid rather than the presence of nucleating substrates is suggested to be the controlling factor in the structural development. Where dynamic motion is restricted, as in the interstices of a yarn, mesophase formation and growth are also restricted. Alignment of mesophase material with a substrate is primarily controlled through motion of the mesophase droplets in flow, which generally do not wet the substrate. Certain well-order surfaces are wetted by the mesophase material, but the effect is primarily noted on surfaces of comparable size to the droplets. (Author)