Strength of MgO and NaCl polycrystals to confining pressures of 250 kbar at 25 °C

Abstract

The strengths of MgO and NaCl polycrystals under confining pressures to 250 kbar have been determined in a diamond-anvil high-pressure cell. The stresses in the samples are inferred from the strains determined by x-ray diffraction. The strength of MgO polycrystals is found to rise from a 1-bar confining pressure value of about 4 kbar to a maximum of 30±10 kbar at a pressure of 50±20 kbar and to remain constant at that value to a pressure of 250 kbar. The strength of NaCl polycrystals is found to rise from a 1-bar confining pressure value of about 0.3 kbar to a maximum of 4.0±1.5 kbar at a confining pressure of 250 kbar. The interpretation of the form of strength versus pressure for these two compounds is discussed in terms of a brittle-ductile transition. Preliminary transmission electron microscope data are presented.