Volume 217, Issue 7 - Special Issue dedicated to F. Hensel

Adaptation of the internally-heated autoclave technique to nuclear magnetic resonance (NMR) has permitted NMR measurements of electronically-conducting fluids at high temperatures and pressures. The history of NMR experiments on mercury, selenium, and cesium is reviewed briefly with reference to subsequent relevant research on these materials.

The equation of state of fluid hydrogen, helium, and their mixtures is determined within fluid variational theory. Reactions between the constituents such as dissociation and ionization are considered. Results are given for densities and temperatures relevant for the interior of giant planets. Furthermore, the electrical conductivity is determined within linear response theory. Comparison is performed with available experiments and other theoretical work.

We review here experiments that investigate how the electronic properties of five chemically dissimilar fluid elements, hydrogen, nitrogen, oxygen, rubidium and caesium, vary with density beyond their critical points. Remarkably, all five elements in their metallic regime have essentially the same electrical conductivities, close to the predicted minimum metallic conductivity of a high-temperature, disordered metallic fluid. The large differences in their respective metal-nonmetal transition densities are rationalized in terms of each chemical element’s unique atomic properties of size (radial extent of electronic wave function, N.F.Mott) and electronic polarizability (K.F.Herzfeld and D.A.Goldhammer). These experiments thereby highlight the pivotal role of atomic properties in dictating the metallic or nonmetallic status of chemical elements of the periodic classification.

It is well known that the liquid dynamics slows down on approaching the liquid-gas critical point or the liquid-glass transition. Recently we have found by the sound attenuation measurements that the metal-nonmetal (M-NM) transition also induces slow dynamics. In the M-NM transition range of expanded liquid Hg, we have observed anomalous increase in the sound attenuation due to the structural relaxation process. Assuming a simple Debye-type relaxation, we have estimated that the relaxation time should be of the order of nanoseconds and revealed that the relaxation strength has a broad maximum in the M-NM transition range. Moreover, two types of anomalies have been observed also in the semiconductor-metal (S-M) transition range of liquid Te-Se mixtures. We present the recent experimental results of the sound attenuation measurements and discuss briefly the mechanisms of the slow dynamics in the metal-nonmetal transition range of liquids.

Recently, experimental studies on the dynamical structure of liquid metals have been actively carried out by the inelastic X-ray scattering (IXS) technique using the synchrotron radiation which have stimulated theoretical studies. In this paper, recent progress in theoretical studies on the dynamical structure of liquid metals are described in two approaches, i.e. the theoretical approach based on the memory function formalism and the various kinds of computer simulations.

We conducted detailed measurements of the apparent specific volume of dipalmitoylphosphatidylcholine (DPPC)–cholesterol mixtures in excess water as a function of pressure up to 70MPa (700bar) at 20, 38 and 50°C. The volumetric properties and the isothermal compressibility κ T of the lipid vesicles were determined at cholesterol concentrations, χ chol , ranging up to 50 mol. The thermodynamic data are compared with other physico-chemical properties of phospholipid–cholesterol mixtures. Furthermore, the thermodynamic properties of the system are discussed in the light of the various T , χ chol –phase diagrams and computer simulation studies published in the literature.

The results of neutron diffraction and EXAFS measurements for l-Te and l-As-Te mixtures (10, 20, 30 and 40at. As) are discussed. The g ( r ) patterns of l-Te show a substantial overlap between the first and second peaks. The first minimum after the first peak of g ( r ) around 3.2Å is filled up at high temperature. Upon the addition of As to l-Te the first peak of g ( r ) becomes sharp, implying that As atoms bridge between Te chains and suppress the thermal fluctuations of the inter-chain distances. The filling of the first minimum around 3.2Å observed for l-As-Te mixtures at high temperature is associated with the inter-chain correlation in a densely packed configuration. From the EXAFS analysis of l-As-Te mixtures we conclude that the network structure composed of threefold coordinated As atoms and twofold coordinated Te atoms is transformed into a twofold coordinated chain structure. The network-chain transformation is accompanied by a gradual semiconductor to metal transition. The first sharp diffraction peak observed for l-As 20 Te 80 and l-As 40 Te 60 is related to the Te-Te intermediate range order in -Te-As-Te- or -Te-As-As-Te- chain molecules.

Neutron diffraction measurements for liquid (l-) Te have been performed. The first minimum after the first peak of g ( r ) is well above zero and filled up with temperature, while the second peak diminishes substantially and flattens out at high temperature. The temperature variations of g ( r ) are analyzed combining the structural information available from our EXAFS results. The curve fitting of g ( r ) for l-Te predicts that two different inter-chain components coexist. The first corresponds to the short-distance inter-chain component around 3.2Å and the second corresponds to the long-distance inter-chain component around 3.8Å. The filling of the first minimum around 3.2Å at high temperature is clearly related to the metallization. EXAFS analysis on the basis of the model g ( r ) indicates that the short-distance inter-chain component (P2) responsible for the metallic conduction in l-Te as well as the nearest intra-chain component (P1) are required for fitting the oscillatory spectrum in the region of short-range sensitivity of the EXAFS signal. It is concluded that the S-M transition observed for l-Te arises from the transformation to the densely packed configuration composed of shortened chain molecules.

Spectroscopic ellipsometry and reflectometry were employed to study the wetting behaviour of the metal–molten salt system K x (KCl) 1− x at the interface to an inert sapphire wall. We present new results on the wetting film spectra and on the film thickness at solid–liquid coexistence and in the homogeneous liquid phase. The film spectra clearly show the typical absorption of the liquid state F-centre. The wetting film thickness strongly increases approaching the monotectic temperature along the liquidus line. In the homogeneous regime the film thickness decreases at constant composition with increasing temperature and at constant temperature with decreasing salt concentration in agreement with complete wetting. For the interpretation within the framework of tetra point wetting we have developed a quantitative description of the excess Gibbs energy of the system.

In this work the results of numerous experiments on carbon particle formation in combustion and pyrolysis of various carbon bearing molecules behind shock waves in the wide temperature range from 1200K to 3500K are analyzed. It is shown, that the discrepancy in the temperatures of the maximum particle yield could be attributed to the differences in the endothermicy of the pyrolysis of various molecules and the maximum optical density at 633nm in all mixtures can be related to the same temperture T =1600K. Based on this consideration, several statements were formulated. First – particle growth in all mixtures can be described by the uniform dependence of optical density D (at 633 nm) on time D ~ a τ 0.4 indicating, that particle formation proceeds via homogeneous condensation. The second – decrease of the optical density at 633nm with the temperature rise is caused not by the decrease of particle yield, but the decrease of their size resulting in the fall of extinction at the given wavelength. Third – the reason of the fall of the final particle size with the temperature rise is the acceleration of the initial cluster formation process and a corresponding increase of the particle number density. And the last statement – the secondary particle growth, observed at T >2200K is completely determined by the primary clusters (nucleus) formed behind the incident wave and the coagulation of small carbon particles formed behind the reflected shock wave using these clusters.

It is established that during the thermal diffusion of weak electrolytes in dilute aqueous solution the total transported enthalpies of the molecular and ionic form of the solute component are practically identical.