Changes in the microstructure and characteristics of carbon/carbon composites with mesophase mesocarbon microbeads added during graphitization

Abstract

Carbon/carbon (C/C) composites were prepared from oxidative PAN fiber felts, a resol-type phenolic resin, and mesophase pitch derived from coal tar. In this study, the effects on mesocarbon microbeads (MCMBs), flexural strength, flexural moduli, electric conductivity, and thermal conductivity of C/C composites with a mesophase content ranging from 0 to 30 wt % were examined during pyrolysis. The results show that the C/C composite with the addition of 10 -30 wt % mesophase had a higher density, greater stacking size, and higher preferred orientation than the C/C composites without any mesophase during heat treatment. These composites also exhibited an improvement in flexural strength from 19.7 to 30.3%. The flexural moduli of these composites with mesophase added increased by 15.1 to 31.3% compared to that with no mesophase added. These composites also showed improved electric conductivity, from 15.1 to 43.7%, and thermal conductivity, from 12 to 31.3%.

Effects of graphite filler loading and heat treatment temperature on the properties of phenolic resin based carbon–carbon composites

“…Whereas in carbonized samples, up to 20 wt% of filler loading, the moduli of the composites increase as the heat treatment temperature is increased, because the thickness of the samples does not change as compared to their as‐cured samples. The modulus of carbon matrix also improves as a result of orientation and growth of carbon basal planes [11], which reduces the deformation ability of the samples. At higher filler loading of 30 and 40 wt%, the stiffness behaviors of composites change mainly because of the matrix rich region between the carbon fabric layers, which is further due to the increase of thicknesses.…”

“…Whereas in the filler loaded samples, depending on the loading, the microstructure of the matrix is mixture of graphitic and glassy carbons. The matrix becomes strong and stiff because of growth of the carbon basal planes with the heat treatment temperature, which prevent shear failure [11]. At any temperature, the samples without fillers have shown highest value of ILSS compared to the samples with fillers.…”

“…This is explained due to change in the microstructure of the matrix, which is mixture of graphitic and glassy carbons depending on the filler loading, as mentioned in the previous section. The modulus of the matrix improves as a result of orientation and growth of carbon basal planes [11]. Also, the fillers act as a secondary reinforcement and retard the propagation of the preexisting cracks and lengthen their crack path and more energy is expended during propagation of crack.…”

“…In addition, the filler addition also changes the microstructure of bulk carbon matrix in the C/Cs from nongraphitisable to graphitic carbon. These ultimately results in increase in the mechanical properties such as flexural strength and modulus, failure strain, shear strength, fracture toughness, psuedoplastic failure, and the physical properties such as thermal and electrical conductivity of C/Cs depending on the type of carbon fiber reinforcement and its architecture, the type and amount of fillers and the heat treatment temperatures used during processing of the composites [1, 8–12].…”