Abstract
Carbon/carbon (C/C) composites are conventionally manufactured by liquid-phase impregnation (LPI), in which the binder pitches and phenolic resins are impregnated into the composites, and by chemical vapor infiltration (CVI). However, CVI has certain limitations in that expensive gases, such as methane and propane, are used and a long reaction time is required. Therefore, LPI is more widely used, as it employs economical pitches. In this study, the effects of one-step preparation on mechanical properties of C/C composites impregnated with mesophase binder pitches and phenolic resins have been investigated. The C/C composites containing four types of 20 wt.% mesophase binder pitches had differences in softening point (SP) and quinoline insoluble (QI) contents. After conducting trials on mesophase formation using different heat treatment temperatures and times, the best density and mechanical properties of the C/C composites were achieved using the mesophase binder pitches with 170 °C SP. However, when SP 200 °C was used, the density of the C/C composites was not further improved. This is because the binder pitches were not properly impregnated into the composites due to the high viscosity and QI of the binder pitches. Furthermore, the C/C composites fabricated with 20 wt.% pitch 2 exhibited the highest mechanical properties.
Highlights
Carbon/carbon (C/C) composites are carbon materials comprising carbon fibers and carbon matrix resins
The C/C composite impregnated with pitch 2, which has a softening point (SP) of 168 ◦ C, exhibits the highest density (1.45 g/cm3 ) among all the mesophase binder pitches
As the mesophase binder pitches undergo liquid-phase carbonization and pores are generated within the composites, the mesophase binder pitches fully infiltrate the composites, increasing their densities [21,22,23]
Summary
Carbon/carbon (C/C) composites are carbon materials comprising carbon fibers and carbon matrix resins. Many pores and cracks form in C/C composites owing to gas evolution resulting from pyrolysis of the matrix during carbonization These pores and cracks degrade the thermal and mechanical properties of the materials [4,5,6]. Coplanar interlayer flaws caused by processing are clearly expected to affect the interlaminar shear strength (ILSS) of phenolic resin-based C/C composites [11,12,13]. This is a major limitation of this method, and many studies have recently conducted impregnation using a mesophase pitch obtained by pitch deformation. The impregnated green bodies were carbonized at 1100 ◦ C to produce the C/C composites and the effects of impregnating the blends of phenolic resins and binder pitches on density and mechanical properties of the C/C composites were investigated
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