Carbon and Graphite Matrices in Carbon-Carbon Composites: An Overview of their Formation, Structure, and Properties

Abstract : Carbon-carbon (C/C) composites, so called because they combine carbon-fiber reinforcement in an all-carbon matrix, can best be viewed as part of the broader category of carbon-fiber-based composites, all of which seek to utilize the light weight and exceptional strength and stiffness of carbon fibers. In C/C particularly, the structural benefits of carbon-fiber reinforcement are combined with the high-temperature capability of an all-carbon materials system, making C/C composites the material of choice for severe- environment applications. Their dimensional stability, laser hardness, and low outgassing also make such composites ideal candidates for various space structural applications. In this overview report, the various fiber architectures used in composite fabrication, i.e., the manner in which the fibers are oriented relative to each other, are discussed briefly. However, the main topic is the carbon matrix and leads to a review of the different approaches for obtaining carbon matrices; specifically, the use of chemical vapor deposition (CVD) of carbon from natural gas (methane), coal-tar and petroleum pitches, and thermosetting resins. In the latter two approaches, the pitch- or resin-matrix composite first produced is baked or fired, to pyrolyze the organic matrix and yield a carbon matrix. The structure of the carbon matrix is characterized by a variety of techniques: X-ray diffraction, laser Raman microprobe spectroscopy, density measurements, polarized-light microscopy, and scanning and transmission electron microscopy (SEM and TEM).