Tse-Hao Ko

Raman spectrum of modified PAN‐based carbon fibers during graphitization

Graphite fibers were developed from polyacrylonitrile (PAN) fibers which were modified with potassium permanganate. After the transitional temperature, the formation of graphite structures commenced, the crystals increased in thickness, and the preferred orientation of the fiber crystals increased. The Raman specific absorption peak of noncrystalline carbon layers (1360 cm−1) weakened with the increase in the graphitization temperature, whereas the degree of graphitization rose. The results of this analysis indicate that manganese has the effect of catalyzing graphitization, thus increasing the mechanical properties of the graphite fibers.

The influence of cobaltous chloride modification on physical properties and microstructure of modified PAN fiber during carbonization

Modification of polyacrylonitrile (PAN) fibers with cobaltous chloride has increased crystal size, crystallinity, and density, and also improved tensile strength and modulus of the resulting carbon fibers. In this study, the effect of cobaltous chloride modification on the physical properties, microstructure, and elemental composition of PAN fibers during the carbonization process was examined. The resultant carbon fibers developed from modified PAN fibers had a lower formation temperature of carbon basal planes than those fibers that developed from the original one. The modification process not only improved the tensile strength but also increased the tensile modulus by about 15% of the resulting carbon fibers at carbonization temperature of 1300°C. A higher stacking size (Lc), or a greater carbon basal plane in crystalline, is one of the reasons to improve the modulus and conductivity of the final carbon fibers. The modification process also increased the electrical conductivity by about 15% at 1300°C and by about 150% at 2500°C.

Raman spectroscopic study of the microstructure of carbon films developed from cobalt chloride-modified Polyacrylonitrile

Polyacrylonitrile (PAN) was modified with cobalt chloride at 90°C for 5 min. The carbon films prepared from original and modified PAN films were carbonized up to 1300°C. The structure of the resulting carbon film was studied using X-ray diffraction and Raman spectroscopy. The stacking size obtained from X-ray diffraction approaches the L c value of the resulting carbon films as the heat treatment temperature increased. The mean average carbon basal planes in crystalline (Lc/d) also increased with increasing pyrolysis temperature. Raman spectra confirmed the progressive structural ordering as treatment temperature increased. During pyrolysis, a substantial decrease in the intensity of the band near the 1350 cm -1 region was observed, indicating a decrease in the disordered structure. The crystal size (L a ) of the resulting carbon films also showed a remarkable increase with increased heat treatment temperature. The resulting carbon films developed from the modified PAN films had higher L c and L a than those developed from the original PAN film. It was established that cobalt catalyzes graphitization of amorphous carbon during pyrolysis. This modification not only promoted the growth of crystal size but also increased the close packing of the carbon basal planes.

Influence of carbon-fiber felts on the development of carbon–carbon composites

Abstract Oxidized PAN-fiber felt was carbonized to 600, 1000, and 1800xa0°C, respectively. Different carbon/carbon composites (C/C composites) were prepared from oxidized PAN-fiber felt, the carbonized felts, and resol-type phenol–formaldehyde resin. These composites were then carbonized and graphized at temperatures of between 600 and 2400xa0°C. The C/C composite made with oxidized PAN-fiber felt showed a strong fiber/matrix bonding, and those developed from the carbonized felt (heat-treatment of 1800xa0°C) showed a poor fiber/matrix bonding. The graphitized composites reinforced with the oxidized PAN-fiber felt resulted in having a high flexural strength (325xa0MPa), and the graphitized composites reinforced with the carbonized felt (carbonized at 1800xa0°C) had a low flexural strength (9xa0MPa). It was found that the stress-orientation promoted the formation of the anisotropic texture around the fibers as well as between the fibers. This felt may very well be able to provide a low-cost route for producing multidimensional C/C composites.

Improvement in the properties of PAN-based Carbon films by modification with cobaltous chloride

Carbon films were developed from polyacrylonitrile (PAN) modified with cobalt chloride. The modification was carried out by immersing PAN in a 5% cobaltous chloride (CoCl2) solution at 90°C for 5 min, oven-dried, and then manufactured into films. The original and modified PAN films were oxidized at 220°C for 2 and 6 h in air, respectively, and finally carbonized at 1300°C. The density, microstructure, elemental analyzer, electrical conductivity, and morphology were all studied. According to the results, it was found that films modified with cobalt chloride have a greater stacking height of carbon-layer planes (Lc), density, electrical conductivity, and nitrogen content after carbonization. Moreover, during the carbonization stage, the cobalt ions promote a catalytic action. The carbon films developed from the modified film not only improved electrical conductivity by 12–38%, but also increased tensile strength by 29–36% and the tensile modulus by 69–110%. Therefore, carbon films having better mechanical properties can be obtained after such modification.