Gun-Young Heo

Precursors and Manufacturing of Carbon Fibers

In this chapter, we will present the precursors and manufacturing of carbon fibers. Among the precursors used for the production of carbon fibers, polyacrylonitrile (PAN)-based and pitch-based precursors are the most important. A significant amount of work has been done on relating the fiber structure to the properties and translating that relationship into production for either reducing cost or increasing fiber properties. However, challenges, including cost reduction, improvement in tensile and compressive strength, and alternative precursor development, still remain. We will also introduce many linear and cyclic polymers for carbon fibers, which are expected to open the door for the low-cost carbon fibers.

Effect of crystallinity on the electrochemical properties of carbon black electrodes

Carbon-based electric double-layer capacitors are being evaluated as potential energy-stor- age devices in an expanding number of applications. In this study, samples of carbon black (CB) treated at different temperatures ranging from 650°C to 1100°C were used as elec- trodes to improve the efficiency of a capacitor. The surface properties of the heat-treated CB samples were characterized by X-ray photoelectron spectroscopy and X-ray diffraction. The effect of the heat-treatment temperature on the electrochemical behaviors was investigated by cyclic voltammetry and in galvanostatic charge-discharge experiments. The experimental results showed that the crystallinity of the CBs increased as the heat-treatment temperature increased. In addition, the specific capacitance of the CBs was found to increase with the increase in the heat-treatment temperature. The maximum specific capacitance was 165 F·g- 1 for the CB sample treated at 1000 o C.

Preparation and characterization of nickel-coated carbon nanofibers produced from the electropsinning of polyamideimide precursor

AbstractNickel-coated carbon nanofibers were prepared using an electroless plating method. The carbon fibers were fabricated with polyamideimide (PAI) by electrospinning, and the characteristics of the nickel-coated carbon fibers were then examined to determine the effect of the nickel coating. The carbon fiber structural properties morphology were confirmed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron spectroscopy (SEM). The electrical conductivity of the fibers was measured using a 4-point testing method. The results showed that the electrical conductivity of the fibers increased with as plating time increased. The electrical conductivity increased remarkably in the presence of metallic nickel particles on the carbon fiber surfaces. This experiment established the optimum conditions for plating on the carbon fiber surfaces that provided the best electrical conductivity.

Thermal Insulation Properties of Epoxy/Mesoporous Carbon Composites

This study aimed to investigate the influence of mesoporous carbons on the thermal insulation properties of epoxy/ mesoporous carbon composites. The mesoporous carbon (CMK-3) was prepared by conventional templating method using SBA-15. The epoxy/mesoporous carbon composites were prepared by mixing the synthesized CMK-3 with diglycidylether of bisphenol A (DGEBA). As experimental results, the curing reactivities of the DGEBA/CMK-3 composites were found to decrease with the addition of the CMK-3. Also, the thermal conductivities of DGEBA/CMK-3 composites were found to decrease with increasing CMK-3 content. This could be interpreted in terms of the slow thermal diffusion rate resulting in pore volume existing in the gaps in the interfaces between the mesoporous carbon and the DGEBA matrix.

Cure behaviors and thermal stabilities of tetrafunctional epoxy resin toughened by polyamideimide

The effect of polyamideimide (PAI) content on the cure behaviors and thermal stabilities of 4,4′-tetraglycidyl diaminodiphenyl methane (TGDDM) epoxy resin/polyamideimide (PAI) blends was investigated. The experimental results revealed that the main exothermic peak and cure activation energy (Ea) of the blends decreased with increasing PAI content, presumably because the curing reaction was accelerated by the presence of secondary amine groups of the PAI backbone. The decomposition activation energy (Ed) of the blends was maximized at 5 phr PAI and decreased above this content; this was attributed to the short-chain structural network in TGDDM/PAI blends, which was derived from etherification and chain-scission reactions caused by the secondary amine of PAI.

Effect of urethane functionality and number of epoxide groups on cure and mechanical behaviors of epoxy resins

We report the synthesis of the novel bi- and tetrafunctional epoxy resins, 2-ECI and 4-ECI, containing urethane functionality. Their chemical structures were characterized by Fourier transform infrared spectroscopy (FTIR) and 1H nuclear magnetic resonance (1H NMR) spectroscopy. The effects of urethane functionality and the number of epoxide groups on the curing behavior and physical and mechanical properties of the epoxy resins were investigated. Compared to 4-ECI, 2-ECI was more reactive with the curing agent methyl hexahydrophthalic anhydride. However, the shear strength and critical stress intensity factor values of the cured 4-ECI resin were significantly higher than those of the cured bisphenol-A diglycidylether and 2-ECI resin, which was attributed to the synergistic effects of urethane functionality and high cross-linking density in the cured 4-ECI resin.

Thermal and cure shrinkage behaviors of epoxy resins cured by thermal cationic catalysts

The thermal and volumetric change properties of diglycidyl ether of bisphenol A (DGEBA) epoxy resin were studied using two thermal cationic catalysts: benzylquinoxalinium hexafluoroantimonate (BQH) and triphenyl benzyl phosphonium hexafluoroantimonate (TBPH). The cure reactivity and thermal stability of the DGEBA/BQH system were higher than those of the DGEBA/TBPH system; this was because of the slow thermal diffusion rate of the DGEBA/TBPH system induced by the bulky phenyl groups in TBPH. The volumetric change values of DGEBA/BQH and DGEBA/TBPH were −0.17% and 7.95%, respectively.