Elastic properties and electrical conductivity of mica/expanded graphite nanocomposites

Abstract

Monolithic mica/expanded graphite nanocomposites were prepared from a mixture of expanded graphite (EG) and a fine powder of mica phlogopite. By compressing more or less the mixture, monoliths with densities ranging from 0.033 to 0.225 g cm −3 were obtained. Electrical conductivity and elastic moduli of about 30 samples were investigated. Stiffness of composites was discussed in relation to the mica content, direction with respect to the bedding plane and component elasticity. Elastic and electrical properties evidence the ordering of the structure along the bedding plane, resulting in sufficiently good elastic and electrical properties. Perpendicularly to the bedding plane the presence of mica improves the elastic properties but makes electrical properties worse. A simple model predicting the composite elastic modulus from the component parameters was found to describe very well the elastic properties of composites parallel to the bedding plane (structural continuity in this direction). Some divergence between E ⊥ theor and E ⊥ exp suggests a structural discontinuity perpendicular to the bedding plane. Among the present phases (graphite, mica and pore space), only graphite is conducting. Introducing an increasingly high amount of mica makes the conductivity decrease; however, below 20 wt.%, the effect is rather low with respect to pure compressed EG. Hence, rigidifying the latter by making mica-based nanocomposites is possible without appreciably degrading the conducting properties.