Microstructure Characterization And Property Analysis Of Carbon Fibers

The microstructure, the elements ingredient and contents, the microcrystalline structure, the chemical structure and the morphological structure of domestic T300, T700, T800 and Japan T700 carbon fibers were investigated by scanning electron microscopy(SEM), X-ray diffraction(XRD), Raman spectroscopy and transmission electron microscope(TEM). The relative size of hardness was studied by atomic force microscopy(AFM). The differences of the four carbon fibers and the influence of the differences on mechanical properties were compared. It can provide scientific theoretical directions for the production of domestic carbon fiber of high performance. Also, it can offer some references for selecting carbon fiber when preparing composite materials.The results of SEM indicated that the fracture morphology of Japan T700 was the most close to circular, the roundness value was approaching to 1. The diameter of domestic T300, T700 and Japan T700 was all about 7μm, but 5.4 μm of Domestic T800. The grooves on the surface of the domestic T300 carbon fiber were deeper and wider than domestic T700.The grooves of domestic T300 had the largest number. The surface of domestic T800 only existed some shallow texture. The surface of Japan T700 was smooth, almost no grooves existing. The smaller the diameter of the carbon fiber is, the smaller probabilities of internal defects and the higher strength the carbon fiber there will be. So the tensile strength of domestic T800 was better than domestic T300 and T700. Domestic T700 possessed of better wetting property with resin matrix due to many prominent grooves on the surface. But the grooves resulted in decrease of tensile strength. The four elements C, N, O and Si were all contained in the four kinds of carbon fiber, and the main composition was C(more than 90%). Domestic T300 possessed the minimum C content and the highest N content. The tensile strength of T300 was significantly lower than the other three.The results of XRD and Raman indicated that the size of crystallite, stacked layers and the degree graphitization of Japan T700 were superior to domestic T700. Domestic T800 was better than domestic T300 and T700. The photo of TEM revealed that the lattice fringe was more orderly and the proportion of crystalline phase increased from domestic T300 to T800. The lattice fringe of T800 was parallel to the axis of fibers. So the regularity of graphite layers was in order of domestic T800 more than domestic T700 more than domestic T300. The Japan T700 was better than domestic T700 in a similar way. It can be proved that the size of crystallite and the degree of graphitization of carbon fiber had a significant effect on its mechanical properties.The hardness of Japan T700 was greater than domestic T700. From domestic T300 to T800, the hardness increased gradually. The different micro-mechanical properties of carbon fiber led to the difference in tensile modulus.The analysis of the microstructure of carbon fiber indicated that decreasing the diameter, increasing the roundness, reducing the quantity of surface grooves and improving the size of crystallite and the degree of graphitization contributed to the improvement of the mechanical properties of carbon fiber.