Aging process of electrical contacts in granular matter

The electrical resistance decay of a metallic granular packing has been measured as a function of time. This measurement gives information about the size of the conducting cluster formed by the well connected grains. Several regimes have been encountered. Chronologically, the first one concerns the growth of the conducting cluster and is identified to belong to diffusion processes through a stretched exponential behavior. The relaxation time is found to be simply related to the initial injected power. This regime is followed by a reorganisation process due to thermal dilatation. For the long term behavior of the decay, an aging process occurs and enhances the electrical contacts between grains through microsoldering.