Relations between microstructure, electrical percolation and corrosion in metal-insulator composites

Five series of compacted granular metal-polymer composites were prepared in a wide range of metal volume fractions. The metals are Al, Fe, Ni, W and Zn powders. The polymer in powder form is the poly-phenylsulfur [-C6H4S-](n) noted as PPS. Using electrical complex impedance spectroscopy (ECIS) measurements, the a.c. electrical properties of these composites were analyzed as a function of metal volume fraction and of working frequencies. Each material was characterized by scanning electron microscopy to determine the distribution and morphology of the particles. Close to the percolation threshold, abnormal electrical behavior was observed and interpreted using scanning electron microscopy (SEM) analysis. Two types of modeling calculation are proposed to describe the electrical properties. A model inspired by the Effective Medium Approximation (EMA) improves the modeling approach: the mechanically induced modification of grain size and distribution is interpreted in terms of new modeling parameters governing the evolution of the conductance. A description of electrical behavior close to the percolation threshold is proposed using percolation theory. Critical exponents are determined above and below the percolation compositions. Finally, a study of corrosion behavior for Zn based composites is presented and correlated with the initial electrical behavior of these composites. (C) 2002 Elsevier Science B.V. All rights reserved.