Volume 73, Issue 5

The Tunisian salt lakes are considered as an important materials resource useful for industry and agriculture. They are called sebkhat or chott, and they cover a large part of Tunisian land. Their brines correspond to the quinary system: Na + , K + , Mg 2+ / Cl­, SO 4 2 ­­H 2 O. In the first part of this paper, a short description and abstracted geochemical and economical data about some Tunisian salt lakes are given. In the second part, the fitting equations used for modeling the quinary system are established and applied to the subsystems NaCl­KCl­H 2 O, NaCl­MgCl 2 ­H 2 O, KCl­MgCl 2 ­H 2 O, and to NaCl­Na 2 SO 4 ­H 2 O, KCl­K 2 SO 4 ­H 2 O, Na 2 SO 4 ­K 2 SO 4 ­H 2 O. The coherence between the calculated and the experimental diagrams is discussed.

This presentation focuses on condensed phases within the broader area of phase diagrams at high temperature and high pressure.

The prevention and treatment of crystal deposition in the human body are based on the understanding of the physicochemical properties underlying the precipitation of the substances involved. Among these properties, the solubilities of the crystals are very important. Recently, experimentally determined solubility data of substances related to urolithiasis, such as calcium oxalate hydrates, uric acid and urates, cystine, and xanthine, were critically assessed. Unfortunately, reported solubilities of these substances were found to be either scarce or in large disagreement. Consequently, detailed studies were carried out in our laboratory, and the results will be discussed in this communication with emphasis on the thermodynamic consistency of the experimentally determined data. Since proper modeling of the solubilities of these substances in artificial urine solutions serves as a prerequisite for solubility predictions in real urine, the Joint Expert Speciation System (JESS) software package was employed to create a comprehensive computer model including the relevant, low-molecular inorganic and organic components of urine. The results of the simulations lead to some useful suggestions regarding the prevention and treatment of stone disease.

As innovative means to recover actinides from irradiated fuels, pyrochemical processes are proposed. In the Japan Atomic Energy Research Institute (JAERI), the feasibility of applying molten-salts processes to nitride fuels containing transuranium elements for transmutation is investigated. In the course of study, experiments and analyses have been made on the high-temperature chemistry of M­N­Cl systems, the effects of oxygen impurities, and the implications of the divalent state along with the normal trivalent state of lanthanides and actinides. Thermodynamic calculation and the electrochemical measurements are compared in a few aspects of dissolution and precipitation of nuclear materials in molten halides.

The group of binary common-ion alkali halide systems correspond to an excellent vehicle for discussing and demonstrating the influence of mismatch in sizebetween the building units of the host crystal and the units of the gueston the formation of mixed crystals and the limits of solid-state solubility. The numerical values of just four constants are needed to formulate a uniform thermodynamic description of the mixed crystalline state of the group of systems. In terms of deviation from ideal mixing behavior, in terms of the excess Gibbs energy, two constants are needed to relate the magnitude of the function to mismatch in size. One constant is to account for the asymmetry of the function, and one to express the dependence on temperature. The values of the constants have been assessed with the help of data available for 13 systems showing complete miscibility. The uniform description allows one to calculate, for every system of the group, the solubilities of the components in one another at any temperature.

Since 1979, the International Union of Pure and Applied Chemistry (IUPAC) Commission V.8 on Solubility Data has published over 70 compilations of evaluated data on the solubility of gases in liquids, liquids in liquids, and solids in liquids. These volumes represent one of the largest collections of chemical property data ever produced and are the result of work of scientists throughout the world. In 1998, IUPAC signed an agreement with the National Institute of Standards and Technology (NIST) to continue the series by replacing the monographs by articles in the Journal of Physical and Chemical Reference Data . Five data compilations have already been published in the Journal, and many more are under way. Recently, IUPAC and NIST have concluded another agreement about computerizing all previously published IUPAC solubility data. In this paper, we describe in detail the computerization of IUPAC solubility data, with some emphasis on harmonizing data published over a long time period. We describe the anticipated query paths that will be supported. We also discuss some of the driving forces for making these and other data resources available over the World Wide Web.

In this paper the application of Pitzer's equations for modeling of solubility equilibria in the hexary oceanic salt system Na + , K + , Mg 2+ , Ca 2+ // Cl­, SO 4 2 ­­H 2 O and its subsystems over large temperature intervals is discussed. Lack of ternary solution data considerably restricts the use of the equations as an evaluation tool for the quality of solubility data. Models optimized for the available data in two temperature intervals have been derived. Since Pitzer's model gives no guidance for temperature dependence, the number of parameters is dominated by temperature coefficients. Thus, for extended temperature intervals other approaches like the Cohen-Adad formalism can be advantageous in solubility data evaluation.

This document is the first published by the IUPAC Commission on Macromolecular Nomenclature dealing specifically with liquid crystals. Because of the breadth of its scope, it has been prepared in collaboration with representatives of the International Liquid Crystal Society. The document gives definitions of terms related to low-molar-mass and polymer liquid crystals. It relies on basic definitions of terms that are widely used in the field of liquid crystals and in polymer science. The terms are arranged in five sections dealing with general definitions of liquid-crystalline and mesomorphic states of matter, types of mesophases, optical textures and defects of liquid crystals, the physical characteristics of liquid crystals (including electro-optical and magneto-optical properties), and finally liquid-crystal polymers. The terms that have been selected are those most commonly encountered in the conventional structural, thermal, and electro-optical characterization of liquid-crystalline materials.