Previous page     Contents     Next page

3.6 Melt Physics and Chemistry

Many of the current projects at the Geoinstitut continue to be devoted to improving our understanding of the physics and chemistry of silicate melts. In previous years, these efforts might have focused on more diluted topics, or might have been constrained to simpler chemical systems. Now, however, after more and more of the fundamental issues in silicate melts have been rigorously addressed, we have begun to take aim at some of the more intriguing questions facing us in the area of magmatic systems. A large part of this undertaking is still being accomplished through the determination of silicate melt viscosities. Viscosity can be measured over a range spanning several orders of magnitude, and is extremely sensitive to small variations in both temperature and chemical composition. This makes viscometry an ideal tool for probing into the effects of volatiles dissolved in melts, where dramatic changes in viscosity are observed with mere trace additions of volatile constituents such as water, whereas only minor effects have been noted by the addition of chlorine. In volatile-free polymerized melts, viscosity measurements have even contributed to a better understanding of melt structure, and we must now recognize the importance of structural units known as "triclusters" in addition to standard bridging and non-bridging oxygen species. Expanding our limits in the laboratory has also enabled new directions to be taken. Knowledge of element distribution between immiscible liquids has been improved by use of a novel rotating centrifuge autoclave. Higher temperatures can be reached in the determination of silicate liquid densities, an important advancement in order to cover a wider range of silicate melt composition. X-ray absorption methods like XANES continue to be powerful means of investigating the structural role of various cations in complex glassy materials, and the advent of ELNES (Electron Loss Near Edge Structure) spectroscopy using a transmission electron microscope has enabled similar information to be obtained in-house. One- and two-dimensional solid state NMR spectroscopy is approaching a level similar to that of proton NMR in past decades, such that distinct molecular species can be detected to provide insights into the solution mechanisms of various elements in silicate liquids. The details of these and additional projects are described below. Common to all of the contributions is an underlying commitment to bridge the experimental realm of melt physics and chemistry to the reality of magmatic processes which occur in the Earth.

Bayerisches Geoinstitut, Universität Bayreuth, 95440 Bayreuth, Deutschland
Tel: +49-(0) 921 55 3700 / 3766, Fax: +49-(0) 921 55 3769, E-mail: bayerisches.geoinstitut(at)