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

Abstract

An electrode gauge for particle velocity is used to study condensed substances that acquire high electrical conductivity under shock compression. Thin metallic electrodes are placed into the substance. A shock wave propagates over the substance along the electrodes in a transverse magnetic field. A moving conducting substance closes the electrodes and generates an electromotive force on them. To justify the operation principle of the electrode gauge, the electrical conductivity of selenium and aluminum powders is measured. The high electrical conductivity of the powders (up to ≈10 4 Ω −1 · cm −1 ) allows the electrode gauge to be used for determining the kinematic characteristics of the shock wave. The voltage on the electrodes is proportional to the mean value of particle velocity in the probing conducting layer located directly behind the shock front. Introduction of additional electrodes into the measurement cell allows the wave velocity to be found. This technique is used to plot the shock adiabats of selenium and aluminum powders of different densities. The experimental data obtained are presented as linear dependences of wave velocity on particle velocity. For a powder with large particles, the thickness of the probing layer is commensurable with the shock-transition width. This offers a possibility of using the electrode gauge to study the structure of the shock transition and the phase of substance metallization.

Experimental study of shock-wave magnetic cumulation

“…5 as a function of the shock-wave velocity D m . Figure 5 also shows the ratio u/D versus the shock-wave velocity D. The ratio u/D is obtained from the known shock adiabats for the powders [9,[30][31][32][33]. As is seen from Fig.…”

“…This result is contradictory from the viewpoint of model (1), but it can be qualitatively explained by the influence of electrical conductivity of the shock-compressed substance. According to [29,30], the electrical conductivity of the Al-1 powder, which has a greater density, is higher. Model (1) implies that the electrical conductivity of the working substance is infinitely large.…”

“…Second, a lower shock pressure in the fine powder (generated by the gliding detonation wave) exerts a favorable effect on electrical conductivity of the shockcompressed substance. Indeed, according to [29,30], a decrease in pressure (down to a threshold value) leads to an increase in electrical conductivity.…”

“…This behavior can be attributed to the specific feature of the structure of the shockinduced conductivity wave in the metal powder. The experiments with an electromagnetic electrode gauge [30] show that noticeable conductivity in the coarse alu- minum powder arises in the shock-transition zone at a point where the substance compression is incomplete. Apparently, this result is caused by destruction of thin oxide films on the surface of metal particles under small compaction.…”

“…We were interested whether the model can be used to describe the process of magnetic compression in real substances. New data on electrical conductivity and shock compressibility of aluminum powders [29,30] were used to solve the problem posed.…”