Electrical conductivity of metal powders under shock compression

The electrical conductivity of a series of metal powders under shock compression is measured by an electrocontact technique. Initially, the metal particles are covered by an oxide film, and the powder is non-conducting. Under shock compression, the powder acquires macroscopic conductivity. The electrical conductivity of the shock-compressed powder depends substantially on the metal, porosity, particle size, and shock-wave pressure. The macroscopic electrical conductivity behind the shock-wave front is uniform within the experimental error. The dependences for fine and coarse aluminum powders on the shock-wave pressure are found. It is demonstrated that these dependences are nonmonotonic. For high shock-wave pressures, the electrical conductivity of the substance decreases. This behavior is assumed to be related to strong temperature heating of the substance under shock compression. Estimates of temperature show that shock compression can induce melting and partial vaporization of the metal. The same is evidenced by the behavior of electrical conductivity whose value for fine particles is close to the electrical conductivity of the melt. The electrical conductivity of the coarse powder is heterogeneous because of the strong thermal nonequilibrium of the particle during shock compression. An analysis of results for different metals shows that the basic parameter responsible for electrical conductivity of the shock-compressed powder is the dimensionless density.