Influence of casting velocity on surface resistivity of epoxy-hard coal graded composites

Purpose: of this paper was to describe electrical properties of epoxy-hard coal functionally gradient polymeric materials. The experimental part describes preparation of the cylindrical samples of the polymeric gradient material by centrifugal casting method. Influence of casting velocity on electrical surface resistance and surface resistivity was measured and analysed. Design/methodology/approach: The specimens were prepared using centrifugal casting method. Composites with epoxy resin as a matrix and with respectively 3; 4.32; 7.5; 10.68 and 12%vol of two hard coal types as a filler were cast. Surface resistivity was applied as a measure of electrical properties. The idea of the test was to define electrical resistivity in radial direction with different content and type of conductive component (hard coal). First, specimen's diameter was measured and electrical resistivity was tested. Next, outer layer with thickness about 0,1 mm was removed by turning and electrical measurements performed. The procedure was repeated for all subsequent layers. Findings: The experimental results demonstrated that casting velocity have pronounced influence on surface resistivity of these materials. Hard coal together with epoxy resin formed gradient composite material with different filler content in subsequent layers. Research limitations/implications: The generated graded structure could be controlled only in limited extend by varying rotation speed and material characteristics of components, such as hard coal content and particles size and shape. Originality/value: Hard coal particles were distributed in epoxy resin by centrifugal casting method in order to create functionally graded materials (FGMs). At present, no information is available on the influence of the casting velocity on the electrical properties of these composites. This paper is original also because in the research programme electrical properties of new type of polymeric gradient composites were tested and presented.