Improved Mechanical Strengths of Epoxy Composites Obtained from Ion Beam Treated Carbon Fibers
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02172-0001
ABSTRALCT Carbon fibers derived from various sources are surface modified by oxygen and nitrogen ion beams generated from a low voltage ion source. The surface analyses by X-ray photoelectron spectroscopy reveal that the ion treatment produces large abundances of various surface functional groups which are dependent on impinging ion energies and irradiation times. In the oxygen beam, the hydroxyl moiety is a dominant surface functionality, but in the nitrogen beam, various moieties containing oxygen and nitrogen are observed. The transverse tensile stresses of the epoxy composites made from the ion treated fibers are found to increase two to four times. The ion beam process yields the highest adhesive strength among all surface treatment methods. INTROIXJCTION Carbon fiber (CF) has been widely used as a major reinforced substance for structure materials [1]. The strength and the extent of a reinforcement is dependent on fiber surface chemistry and morphology. Yet, the exact mechanism between fiber surface and matrix for better adhesion is not well understood. In this paper, four commercial carbon fibers of different origins are surface treated by nitrogen and oxygen ion beams to enhance the surface characteristics. The surface chemistry is examined by X-ray photoelectron spectroscopy (XPS) and the adhesive strength by transversed tensile stresses (TTS) of the fiber reinforced epoxy composites. The enhanced strength observed from the present ion processing could be derived from increased surface roughness and abundant chemical functionalities [2-5]. EXPERIMENTAL Fiber samples Four commercial fibers used in this experiment were fibers, HM-3131 (PCF) Tonen Co. and Donacarbo-500 (OF5) and two polyacrylonitrile (PAN) based fibers based CF, Hercules, USA and Besfight IM600 (TCF) Toho Rayon Co.,
two pitch based carbon Osaka Gas Co. Japan, Magnamite IM6 (HCF) Japan.
Ion Beam treatment The oxygen and nitrogen ion beams were generated from a low voltage ion source in a custom made vacuum chamber [3]. Fiber strands about 4" long were clamped on ends onto the perimeter of two wheels affixed to a slowly rotating shaft normal to the ion beam radiation. The ion energy in the range 400-1000 V with varying ion dosages was used for XPS specimens. However, constant voltages of 800 V for oxygen ion, and 400 V for nitrogen ion were employed in the preparation of TTS specimens.
381 Mat. Res. Soc. Symp. Proc. Vol. 318. ©1994 Materials Research Society
XPS analysis The XSAM800 instrument made by KRATOS analytical Co. with Mg K X-ray radiation was used to obtain XPS spectra of CF surfaces. In the &nalyses, t specimen was made only from HCF bundles about 20 tows laid parallel in an ar approximately 1/2" width and 3/4" long. Two surface properties were obtaine' [6]: (1)Atomic surface concentration calculated from the integrated area peaks in wide scan spectra, and (2) Abundances of under the N , 0 and C.,. surface functional groups obtainable from peak profile analyses. Fabrication of Composite The composite test specimens w
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