Quasi-isentropic compression

Chhabildas, L.C. and L.M. Barker (1988), Dynamic Quasi-Isentropic Compression of Tungsten, in Shock Waves in Condensed Matter (edited by S.C. Schmidt and N.C. Holmes), Elsevier Science, New York, pp. 111-114. 

Keywords fullerite, conductivity, shock waves, manganin gauges, quasi-isentropic compression... 

The purpose of the second part of the present research is measurement of conductivity of fullerene C6o crystals under high pressures more than at the former experiments to find out metallization C(, is possible. In the latest experiments we used a mode of multi-step quasi-isentropic compression of fullerene crystals by series of consecutive flat shock waves which enables us to reach much higher... 

The result of typical experiment of measurement of conductivity of C6o under multi-step quasi-isentropic compression up to final pressure 30 Gpa is presented on Fig. 2 as time dependences of sample conductivity and pressure, measured with help of manganin-foil pressure sensor. It is visible as we can see that at the beginning conductivity of a sample sharply increases and then starts to decrease smoothly despite of proceeding increase of pressure. As against to range 0-15 GPa... 

That this is not always the case should be expected. In fact, if it was not for heterogeneous localization of some flow phenomena, it would be very diflicult to initiate secondary explosives, or to effect shock-induced chemical reactions in solids. Heterogeneous shear deformation in metals has also been invoked as an explanation for a reduction in shear strength in shock compression as compared to quasi-isentropic loading. We present here a brief discussion of some aspects of heterogeneous deformation in shock-loaded solids. 

In the first part of present work specific conductivity of fullerene C60 crystals has been measured under smooth quasi-isentropic loading conditions up to 15 GPa at initial temperatures T=293 K and 77 K. We have registered the sharp increase of conductivity more than 6 orders of magnitude in a range of pressure from 0 to 15 GPa, Fig. 1. Value of conductivity regains initial properties after dynamic load is removed. The results received testified about sharply decreasing of band-gap of C6o under compression. However the experimental temperature dependence of... 

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