An apparatus is described which allows studies to pressures of 100 kilobar and to temperatures of 0.03 K. A low temperature hydraulic press is incorporated with a dilution refrigerator to permit the continuous variation in pressure while at low temperature; thus, the entire pressure study of a material can be accomplished in one low temperature run. The sample is sensed magnetically using a SQUID magnetometer to detect changes in its magnetic moment. Operation of the system is described for measurements of the transition temperature of aluminum as a function of temperature and pressure.
A three-layered rhombohedral form of molybdenum diselenide has been produced by subjecting the normal two-layered hexagonal form to pressures of 40 kilobars and temperatures of 1500 degrees C. The new form is isostructural with rhombohedral molybdenum disulfide.
Rotating-anvil type shear presses have been used by several investigators in studies of shear strength and friction on thin samples. The essential design features and operating procedures used by previous investigators are briefly reviewed. A new apparatus of this general type is then described which incorporates a high-sensitivity, strain-gauge instrumented, combination load and torque cell. The new device was designed specifically for measurements on very weak solids at pressures up to about 20 kbar. Operation of the apparatus is illustrated with measurements at pressure up to 5 kbar on thin sheets of the polymer polyvinylidene fluoride. The results are interpreted in terms of the friction and shear strength of the sample material by making use of concepts from the adhesion theory of friction.
The shear strength of grossly deformed cop~er, silver, and gold has been meas~red ~n an opposed anvil shear apparatus at pressures up to 150 khar m the temperature ran?e from ~7 -900 C. Th~ shear data agree with independent strength measurements at low pressures, but differ. sigmfican~l:l:' from high-press~re shear strength measurements by other investigators. The data also fit a SImple empmcal formula relatmg the temperature and pressure dependence of the shear strength.
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