Stephen J. Guggenheim
I try to define research problems that are of special significance in mineralogy and materials research. Generally, these problems relate to the understanding of phyllosilicate (clay mineral) stability, and they include research on:
Clay-hydrate intercalates. Methane hydrates are ubiquitous on the ocean floor and represent a vast reservoir of methane, a greenhouse gas. With A.F. Koster van Groos , we have developed a low-temperature, elevated-pressure powder X-ray diffraction environmental chamber to study hydrate formation intercalated in clay. Initial studies indicate that methane hydrates do indeed intercalate in swelling clays, suggesting an additional reservoir for methane that may have important implications for climate change, for energy-resource development, or for energy-exploration strategies.
Organo-clay interactions. Interactions between organic molecules and clays represent an important part of the field of "environmental mineralogy". Understanding these interactions are critical in developing new materials for remediation of polluted ground water and soil. Structural studies involving organic interstratifications in vermiculite are presently being studied by single crystal X-ray methods. In addition, a high-pressure (1 kbar) DTA system coupled with a gas chromatograph is being developed with A.F. Koster van Groos to study the interactions of other clay materials with organic molecules.
||Dehydration and dehydroxylation reactions. The role of water (H2O, OH) in reactions involving phyllosilicates is fundamental in sedimentary, metamorphic, and diagenetic processes, as well as in many industrial and engineering applications. My research combines high temperature X-ray diffraction techniques with high-pressure DTA to propose atomistic models for these reactions, in addition to the description of the thermodynamic properties.
Modulated phyllosilicates. The characterization of modulated layer silicates is important in the understanding of topological limits and possible chemical variations of normal layer silicates. This work emphasizes the use of high resolution transmission electron microscopy (HRTEM), electron diffraction, and synchrotron radiation to determine complex crystal structures. This structural-solution approach is applicable to most layered materials and is not limited to modulated layer silicates.
Structure studies of phyllosilicates. Understanding the crystal structures of layer silicates is fundamental in predicting the physical and chemical properties of these materials. Current work involves structural studies at high temperatures, in addition to examining phyllosilicates of unusual chemistries.