A diamond‐anvil type optical cell of improved design has produced static pressures in gasketed samples up to 500 kilobar as measured by the ruby fluorescence technique. The ruby R1 line pressure shift is linear to 291 kilobar, and the maximum measured shift is extrapolated to 500 kilobar assuming continued linearity of the pressure dependence. The ultimate pressure capability of this diamond cell has not been established. Transition pressures in the semiconductors Si, ZnSe, ZnS, and GaP measured by the ruby method indicate that the revised 1970 fixed point scale and the ruby (NaCl) scale diverge above 135 kilobar and disagreement may be by as much as a factor of 2 in the 500 kilobar range with the ruby scale defining the lower pressure.

Ultrahigh pressure diamond‐anvil cell and several semiconductor phase transition pressures in relation to the fixed point pressure scale

Hexagonal, graphitelike boron nitride may be changed directly into the zincblende cubic form reported earlier or into a new wurtzite form by the application of static high pressures. No catalyst appears to be necessary. At high temperatures, between about 2500° and 4000°K, the zincblende form is favored; at lower temperatures, down to 300°K, the wurtzite form is favored; frequently both forms appear together. The minimum pressure required for the transformations is about 115 kbar at 2000°K; somewhat higher pressures, of the order of 130 kbar, suffice at higher and lower temperatures. The crystallites of the dense phases are small but give good x‐ray diffraction patterns from which the crystal structures can be determined.

Direct Transformation of Hexagonal Boron Nitride to Denser Forms

Shock compression of solids

High-pressure torsion (HPT) method currently receives much attention as a severe plastic deformation (SPD) technique mainly because of the reports of Prof. Ruslan Z. Valiev and his co-workers in 1988. They reported the efficiency of the method in creating ultrafine-grained (UFG) structures with predominantly high-angle grain boundaries, which started the new age of nanoSPD materials with novel properties. The HPT method was first introduced by Prof. Percy W. Bridgman in 1935. Bridgman pioneered application of high torsional shearing stress combined with high hydrostatic pressure to many different kinds of materials such as pure elements, metallic materials, glasses, geological materials (rocks and minerals), biological materials, polymers and many different kinds of organic and inorganic compounds. This paper reviews the findings of Bridgman and his successors from 1935 to 1988 using the HPT method and summarizes their historical importance in recent advancement of materials, properties, phase transformations and HPT machine designs.

A review on high-pressure torsion (HPT) from 1935 to 1988

Pressure induced phase transitions in silicon, germanium and some III–V compounds

A high pressure electrical cell is described consisting of tapered Carboloy pistons supported by a pyrophyllite pellet. The pistons are heavily work hardened. A calibration is obtained based on the barium transition at 59 kb, the bismuth transition at 90 kb, and an extrapolation of Bridgman's data. The pressure range is to 500 kb under favorable circumstances. New fixed points include a discontinuous rise in resistance of lead at 161 kb, a discontinuous rise in resistance of barium at 147 kb, a discontinuous rise in the resistance of rubidium at 193 kb, a maximum in the resistance of calcium at 370–75 kb, and a maximum in the resistance of rubidium at 425 kb. In addition, there is a discontinuous rise in resistance of iron at 133 kb which is consistent with the shock wave pressure point found at 131 kb and 37°C.

A. S. Balchan

Papers

High Pressure Electrical Resistance Cell, and Calibration Points above 100 Kilobars