Electrical Conductivity of Metal Powders under Shock Compression

Abstract

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 shockcompressed 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.

Electrode gauge as an instrument for studying shock compression and metallization of the substance

“…A further increase in pressure increases the sample temperature, which has an adverse effect on electrical conductivity. The dependence σ(p) obtained here qualitatively agrees with the test results of [11] with PAP-2 aluminum powder. The electrical conductivity of PAP-2 powder is lower than that of PAP-1, which is explained by different densities of the powders.…”

“…The electrical conductivity of selenium powder and PAP-2 aluminum powder under shock compression is given in the present paragraph. An electrocontact shunt circuit was used [3,10,11]. The structure of the measurement cell, layout of experiments, and the procedure of raw data processing were described in [11] and are not discussed here.…”

“…An electrocontact shunt circuit was used [3,10,11]. The structure of the measurement cell, layout of experiments, and the procedure of raw data processing were described in [11] and are not discussed here. Figure 1 shows a typical oscillogram of the test with PAP-2 aluminum powder and the result of its processing.…”

“…The results of oscillogram processing in the variables (V 0 /V − 1, t) are close to a straight line (V 0 is the initial voltage). This means that the electrical conductivity of the shock-compressed substance is uniform behind the shock front [11].…”

“…Various physical mechanisms of metallization are possible: polymorphic transition, thermal ionization, reduction of the energy slot under compression, chemical reaction, changes in the phase composition, etc. Shock compression of metal powders is also accompanied by substantial changes in electrophysical properties [11]. Particles of a number of metal powders (e.g., aluminum) in the standard state are covered by a fairly strong oxide film.…”