Hysteresis of ruby fluorescent line by pressure and annealing effect

Abstract

Accuracy of hydrostatic pressure measurement in a diamond-anvil cell (DAC) depends on the reproducibility of ruby RI fluorescent measurement. The larger scatter in R, fluorescent wavelength shift than the reproducibility of spectroscopic measurement was observed among appropriately mirror-finished ruby plates before setting up in DAC. The characteristics of the scatter changed after loading DAC up to pressure over hydrostatic limit. They vanished by annealing the ruby plates. These phenomena are presumably due to the appearance and disappearance of the residual stress in the ruby crystal. Such hysteresis of ruby fluorescent wavelength shift by pressure and its annealing effect are discussed.     

High pressure studies of viscosity effects on isomerization

Abstract

The viscosity dependence of the isomerization process with comparatively low potential barrier was studied as a model of one-dimensional barrier crossing.

We found that the ground-state isomerization of DODCI fails to fit the Kramers equation. We analyzed this non-Kramers behavior by means of an approach of frequency dependent friction.     

Pressure effects on bacteriophage T4

Abstract

The conformational changes which occur in bacteriophage T4 during infection can be simulated by hydrostatic pressure. The kinetics of the pressure induced process is measured by the decrease of the virus infectivity. Experimental results are explained by assuming that the virus population is composed of three parts which differ in their pressure sensitivity. It is shown that the phages which are the highly sensitive part lose this feature when they are alawly accustomed to pressure.     

Metallization of liquid iodine under high pressure

Abstract

In molten iodine two transitions accompanied by a large increase of conductivity (σ) were found under pressure between 3 and 4 GPa.

During the first transition a increases by approximately 10′ times, the volume changing very slightly or remaining constant. During the second transition a increases by 2-10 times and then is accompanied by a decrease of volume.     

Pressure induced metallization of the antiferromagnetic-insulator CoI

Abstract

High pressure electrical measurements were conducted in the antiferromagnetic insulator CoI, using a miniature Diamond Anvil Cell (DAC). The existence of a Mott Transition predicted from high pressure ¹²⁹I Mgssbauer Spectroscopy (MS)¹ has been verified. At about 8 GPa the system becomes metal1ic as evidenced by the temperature behavior of the conductivity. The conductivity at room temperature, however, still increases with increasing pressure, leveling off at 11 GPa. The metallic behavior in the 8 -11 GPa is explained by coexistence of metallic and insulating clusters via a percolating process. Above 11 GPa the material is completely metallic. This mechanism is consistent with the MS findings.     

High pressure organic chemistry; XV. Non-catalyzed cleavage reaction of ethers with acyl halides

Abstract

A variety of cyclic and acyclic ethers are efficiently reacted with acyl chlorides or acyl bromides to afford the ether-cleaved compounds of ω-chloro-or ω-bromoesters under high pressure conditions. The reactivity of ethers is found to be roughly depend on the basicity of the ether oxygen atom.     

A low-temperature high-pressure apparatus with a temperature control system

Abstract

A low-temperature high-pressure apparatus was designed using commercial cryogenic equipment. Pressures up to 1 GPa and temperatures down to 40 K can be obtained in a volume of up to 30 cm³. The apparatus is of the piston-cylinder type with a piston diameter of 45 mm, and the pressure can be varied at all temperatures, An adaptive temperature control system keeps the temperature inside the pressure cylinder constant to within ±0.1 K.     

Pressure dependent study of semiconductors using semiempirical equations of state

Abstract

Variation of bulk modulus of Si, Ge and GaAs with pressure is studied using four semiempirical equations of state, two of which being proposed very recently. Hence an expression for bulk modulus for arbitrary pressure for the semiconductors similar to Cohen's formula for zero pressure is arrived at. The applicability of these equations of state for the high pressure phases of Si and Ge is tested using the recent experimental and theoretical pressure-volume data of these phases.     

High pressure physics research at BARC

Abstract

High pressure physics research at BARC spans a period of more than two decades and covers the area of both static and dynamic pressures on the one hand and both theoretical and experimental aspects on the other. The experimental facilities available include Diamond Anvil Cells for X-ray diffraction and Raman spectroscopy and a light gas gun. Phase transformations investigated in metallic systems includethose in Cd-Hg, transition metals, rare earths and actinides and these investigations have been supported by detailed band structure calculations and studies of the mechanismof phase transformations. Extensive equation of state studies over a wide range of pressures include a new model for the intermediate pressure range between 0.5 and 10 TPa and interpretation of experimental shock Hugoniots.     

Peculiarities of phase transitions when synthesizing diamond in high pressure apparatus of various types

Abstract

The influence of P, T-parmeters and duration of heat when synthesizing diamond in high pressure apparatus both of recessed anvil-type and cylindrical type (belt-type) on properties of diamond powders was studied. The dependence of pressure in reaction cells on temperature of force elements of apparatus in initial state and on efficiency of high pressure production in a reaction cell before heating was shown.