John Frantz

John Frantz is interested in the investigation of the chemical structure of amorphous materials, such as silicate melts and aqueous fluids, as they pertain to processes involving heat and mass transfer in the terrestrial planets. As the Earth and neighboring terrestrial planets continue to cool, materials are constantly recycled throughout the crust and mantle, resulting in chemically diverse rock compositions. Since amorphous materials are the primary agents in recycling, it is necessary to understand their chemical structure and associated physical properties to understand the processes controlling planetary evolution. In recent years, Frantz has investigated the chemical structure of both silicate melts and hydrothermal fluids.

Frantz has also developed a furnace assembly, which permits for the first time the routine study of polymerization of silicate tetrahedra to temperatures above 1600°C at atmospheric pressure using Raman spectroscopy. He and Bjørn Mysen have successfully used this technique to investigate the structure of silicate melts involving alkalis, alkaline earths, and aluminum.

More recently Frantz's interests have focused on the structure of hydrothermal fluids. His experiments currently involve supercritical fluids using Raman spectroscopy in conjunction with hydrothermal optical pressure vessels. He designed and built an optical cell fitted with diamond windows suitable for in situ measurement of the Raman spectra of fluids to 600°C and 4000 bar for this work.

Frantz is also investigating supercritical fluids containing both water and carbon dioxide -- a vital study since carbon dioxide is a major component of natural hydrothermal fluids. As part of this project, he successfully developed a methodology by which he can directly study CO₂-H₂O binary fluids in situ using Raman spectroscopy. He is also studying the stability and complexing of salts of aliphatic acids in hydrothermal fluids; salts might be important agents for mass transport since they may exist metastably for significant periods of time.

Over the next two or three years, Frantz hopes to conclude these studies and change his research to in situ monitoring and theoretical modeling of natural hydrothermal fluids at oceanic ridges. As a first step in this new direction, he is developing an instrument to measure the hydrogen fugacity of the high-temperature fluids in these environments.

Fig. 9. This is a view of aqueous magnesium sulfate solution shown through a microscope in the heated diamond cell.