Effect of electrical resistivity of Si-Ti-C-O fiber on electromagnetic wave penetration depth of short fiber-dispersed composites

Abstract

High frequency electromagnetic wave has been used for various environments and has especially been required for the fields of advanced wireless communication systems. The system requires electromagnetic wave absorbing material as well as electromagnetic wave reflecting and transmitting materials. Among existing electromagnetic wave absorbing materials, a Si-Ti-C-O base ceramic fiber (Tyranno©R, Ube Industries, Ltd., Yamaguchi, Japan) reinforced polymer matrix composite is expected to have high specific modulus, high specific strength and electromagnetic wave absorbing properties [1, 2]. Recent development of this Si-Ti-C-O fiber allow a wide range of electrical resistivity to be obtained; the electrical resistivity of the fiber has a range from 10−3 to 104 m [3]. However, the effect of fiber electrical resistivity on electromagnetic wave absorbing potential of a composite has not been studied in depth. The present study has been focused on the effect of the electrical resistivity of Si-Ti-C-O fiber on the penetration depth of the short Si-Ti-C-O fiber-dispersed epoxy matrix composites. The chemical composition (at%) of the original Si-Ti-C-O fiber was Ti: 0.78, C: 44, O: 21 and the remainder was Si [1, 3]. The fiber has a circular crosssection with a diameter of 8.5–13 μm and a ∼50 nm carbon-rich layer beneath the surface [4]. Properties of the fiber are listed in Table I [3]. As a received continuous Si-Ti-C-O fiber bundle was mechanically cut into chopped fibers with an average length of ∼2.5 mm. The epoxy matrix was prepared from the mixture of epoxy monomer, hardener, and accelerator, details of the starting materials were reported elsewhere [5–7]. The chopped Si-Ti-C-O fibers were put into the mixture of the components and mixed mechanically. To obtain suitable electrical resistivity of the composite using the percolation effect [8] of the chopped fibers, the mixing was continued for 30 min. This processing condition was selected following a preliminary study of the same composite material [2]. Then, the fiber-epoxy mixture was degassed, poured into a Teflon©R-coated mold and slightly pressed, and thereafter was cured in ambient air at 373 K for 4 h in an oven. The fiber volume fraction in the composite was controlled by the weight ratio of the fiber and matrix. The fiber volume fraction was fixed at 5 vol%. A typical polished section of the composites