Researches at High Temperatures and Pressures

Fluids at high pressures and temperatures

With high pressures, supercritical fluids can be studied over a very wide range of density. Fluids with strongly interacting polar molecules for example water are of particular interest. Results for several thermophysical properties are discussed. Density, dielectric constant and self—ionization of water have been determined or predicted to 1000 °C. Beyond 20 GPa very hot water appears to becom...

Electrical conductivity of wadsleyite at high temperatures and high pressures

New phases of N2O4 at high pressures and high temperatures

High P–T studies of molecular N2O4 using Raman, synchrotron infrared, and X-ray diffraction measurements reveal several new phenomena. Significant changes in the vibrational spectra indicate a phase transition at about 12 GPa. The X-ray diffraction measurements show that the material remains cubic through the transition. We ascribe the transition to a change in the molecular geometry of N2O4 wi...

Diffraction Studies of Order-disorder at High Pressures and Temperatures

Recent developments at synchrotron X-ray beamlines now allow collection of data suitable for structure determination and Rietveld structure refinement at high pressures and temperatures on challenging materials. These include materials, such as dolomite (CaMg(CO3)2) that tends to calcine at high temperatures, and Fe-containing materials, such as the spinel MgFe2O4, which tend to undergo changes...

Thermal properties of iron at high pressures and temperatures.

We investigate the thermoelastic properties of close-packed phases of iron at pressures up to 400 GPa and temperature to 6000 K using a tight-binding total-energy method and the cell model of the vibrational partition function. The calculated properties are in good agreement with available static and shock-wave experimental measurements. The compressional behavior of a number of thermoelastic p...