Recent experimental studies have suggested that colloidal silica can form in high-T (300 to >700°C) hydrothermal fluids (Wilkinson et al., 1996). Natural evidence in support of this was found by Williamson et al. (1997) who proposed a colloidal (gel) silica origin for <50 μm irregularly-shaped inclusions of quartz contained in greisen topaz from southwest England. Confocal and microprobe studies, presented here, strengthen this argument although rather than forming a gel in the hydrothermal fluid, it is suggested that the colloidal silica aggregated as a viscous coagulated colloid, with much of its volume (<10 to 30 vol.%) consisting of metal (mainly Fe) -rich particles. This is evident from the largely solid nature of metal-rich shrinkage bubbles contained at the margins of the inclusions of quartz which shows that the material forming the inclusions contained much less liquid than would be expected in a silica gel. These findings may have important implications for models of ore formation since the precipitation of a coagulated colloid could inhibit hydrothermal fluid transport and cause co-deposition of silica and entrained ore-forming elements. The mode of formation of the colloidal silica and further implications of the study are discussed.

Based on biologically inspired algorithms, a thermodynamic model to describe the vapor-liquid equilibrium of binary complex mixtures containing supercritical fluids and ionic liquids, is presented. The Peng-Robinson equation of state with the Wong-Sandler mixing rules are used to evaluate the fugacity coefficient on the systems. Then, a hybrid particle swarm-ant colony optimization was used to minimize the difference between calculated and experimental bubble pressure, and calculate the binary interaction parameters for the excess Gibbs free energy of all systems used. Simulations are carried out in nine systems with imidazolium-based ionic liquids. The results show that the bubble pressures were correlated with low deviations between experimental and calculated values. These deviations show that the proposed hybrid algorithm is the preferable method to describe the phase equilibrium of these complex mixtures, and can be used for other similar systems.

For the last four decades, the feature sizes of electronic devices for computers have been reduced by a factor of two roughly every 18 months. The result has been a tremendous increase in computational power and reduction in the cost of computing, as measured by cost per function, of nearly 30% annually, so that computations can be done for a billionth of the cost of using the technology of the 1950s. However, devices will soon be so small that the current technology used to produce them will have reached its limits, and the graininess of individual atoms will affect their behavior. This issue focuses on techniques to make tiny devices with dimensions under 45 nm (45 billionths of a meter) for the next generation of devices.Techniques start with coupling currently used 193-nm and 157-nm optical lithography with liquid immersion to reduce the effective wavelength. Other techniques include microprinting, self-assembly, templating, and using supercritical fluids to avoid the effects of surface tension while enabling solution-based processing at such small dimensions. The development of three-dimensional structures that are approaching this scale is also discussed.The methods presented will have an effect on many areas of technology, including, in addition to electronics, advanced sensor technology, energy conversion, catalysis, and nanoelectromechanical systems.

Les propriétés des fluides supercritiques sont à mi-chemin entre celles des gaz et celles des liquides ; ces propriétés peuvent en outre être considérablement modifiées par simple variation de la pression et/ou de la température. Cette spécificité est à l'origine de nombreuses applications dans lesquelles les fluides supercritiques se présentent comme des substituts de choix aux solvants organiques traditionnels. L'extraction et la purification sont les premières applications à avoir été développées ; la facilité de séparation du solvant et des solutés extraits par simple dépressurisation constitue l'atout majeur de cette méthode. Plus récemment d'autres applications très prometteuses ont émergé. Elles concernent les domaines de la réaction chimique, de la chromatographie et du traitement du solide.Initialement freinées dans leur développement par des coûts d'investissement supérieurs à ceux des procédés traditionnels, ces techniques supercritiques connaissent depuis peu un net regain d'intérêt, lié entre autres aux contraintes environnementales de plus en plus fortes pesant sur l'utilisation des solvants traditionnels.