Study of Hall effect on laminated carbon fibre-epoxy composite

Abstract

Conductive polymer composites are important materials for many technical applications. These materials can be used as solar cells, resistors, semiconductor elements, antistatics and electromagnetic shielding materials [1-4]. In our previous publications we attempted to study the electrical characteristics of different polymer composites, at low and high frequency (microwave) range with respect to different types of fillers under different conditions [5-8]. The reported results indicate that the conductivity behaviour of carbon fibre filled polymer composites is governed by complex charge transfer mechanisms such as tunnelling, hopping and interconnecting between fibres. The rate of crosslinking depends on the fibre concentration and their distribution [9, 10]. However, there have been few investigations into the type of majority charge carriers that could be presented in the bulk. For example, it was thought that laminated carbon fibreepoxy composite is likely to exhibits interesting electrical properties. The present work is concerned with calculation of the charge carrier concentration in unidirectional epoxy-laminated carbon fibre composite using the Hall effect concept. We applied the Hall effect technique because it is controlled by surface states. We believe that this technique is practically suitable for materials that have conduction mechanism controlled by hopping or tunnelling processes. Furthermore, this technique was used successfully to measure the compliance of some orientated polymers [11]. The samples used in this study were epoxy composite containing 10, 25 and 36 layers of unidirectional carbon fibres. The prepreg epoxy resin was provided by DuPont (Italy). The physical parameters of this epoxy are given elsewhere [7]. The laminated sheet composites were prepared by embedding carbon fibre layers in epoxy matrix using curing hot pressing techniques. Samples in the form of parallelpipeds were cut from each composite sheet. The electrodes were made of copper evaporated on both sides of the specimen for Hall effect measurements. The measurements were performed at room temperature under constant magnetic field. A conventional Hall effect experimental set-up