Carbon phase transformations under electrodynamic compression

The graphite-diamond phase transition under shock-wave-induced electrodynamic compression has been studied. A sample of a carbon-containing material was loaded by axisymmetric collapse of a copper liner. The liner was acted upon by ponderomotive forces generated by pulsed electric currents with amplitudes of 2–4 MA. The collapse of the cylindrical copper liner with a velocity of ∼1 km/s produced stepped loading of the carbon material in an ampoule from 5 to 40 GPa over 4 μs. Purification of the preserved material yielded agglomerates containing polycrystalline diamond. The average size of diamond polycrystals in the agglomerates is 1–2 μm, and the agglomerate yield is ∼3%. __________ Translated from Fizika Tverdogo Tela, Vol. 46, No. 4, 2004, pp. 659–661. Original Russian Text Copyright ? 2004 by Makarevich, Rakhel, Rumyantsev, Fridman.     

Transition of expanded liquid iron to the nonmetallic state under supercritical pressure

A transition of expanded liquid iron to the nonmetallic state under high pressures (30–100 kbar) at high temperatures (of about 1 eV) is discovered. The result is obtained by direct measurement of the dependence of resistivity on the specific internal energy and volume. Measurements are taken in the specific volume range from the melting curve to values six times higher than the normal specific volume V ₀ in the solid state. It is shown that iron remains in the metallic state up to a relative volume of V/V ₀ = 3–4, at which the resistivity attains a value of about 3–4 μΩ m and becomes almost independent of temperature, while the conduction electron mean free path decreases to the atomic spacing. For V/V ₀ = 4–5, a transition to the nonmetallic state takes place, for which the temperature coefficient of resistance becomes negative and its absolute value becomes much higher than in the metallic state.