Jason Diefenbacher

Al Coordination Changes in High-Pressure Aluminosilicate Liquids

Understanding the effect of pressure on aluminosilicate glass and liquid structure is critical to understanding magma flow at depth. Aluminum coordination has been predicted by mineral phase analysis and molecular dynamic calculations to change with increasing pressure. Nuclear magnetic resonance studies of glasses quenched from high pressure provide clear evidence for an increase in the average coordination of Al with pressure.

Externally controlled pressure and temperature microreactor for in situ x-ray diffraction, visual and spectroscopic reaction investigations under supercritical and subcritical conditions

A microreactor has been developed for in situ, spectroscopic investigations of materials and reaction processes with full external pressure and temperature control from ambient conditions to 400 °C and 310 bar. The sample chamber is in direct contact with an external manifold, whereby gases, liquids or fluids can be injected and their activities controlled prior to and under investigation conditions. The microreactor employs high strength, single crystal moissanite windows which allow direct probe beam interaction with a sample to investigate in situ reaction processes and other materials properties. The relatively large volume of the cell, along with full optical accessibility and external temperature and pressure control, make this reaction cell well suited for experimental investigations involving any combination of gas, fluid, and solid interactions. The microreactor’s capabilities are demonstrated through an in situ x-ray diffraction study of the conversion of a meta-serpentine sample to magnesite un...

Note: Solution NMR probe for the study of CO2 sequestration at elevated pressure and temperature.

Nuclear magnetic resonance is widely employed in studies of chemical reactions and molecular motions at moderate pressure and temperature, but for CO(2) solutions under supercritical conditions encountered in geological or mineral sequestration (pressures to 150 atm and temperatures to 150 °C) a specialized variable-temperature probe is required. The critical component of such a probe is its pressure chamber, and our working design is presented along with examples of its use in (13)C NMR measurements of bicarbonate and dissolved CO(2) fractions as functions of time, following initial pressurization to 70 atm. Also shown are final, steady-state values of these fractions as functions of temperature from 50 to 125 °C at 70 atm.

Silicon Clathrates: Synthesis and Characterization

Two types of silicon clathrates, NaxSi136 (0 o x o 24) and Na8Si46 and a mixed clathrate (Na,Ba)Si46 were synthesized and characterized by X-ray diffraction, 23 Na NMR and high resolution TEM. Systematic changes in X-ray diffraction intensities enabled the sodium content and site occupancy in the NaxSi136 series to be followed and then refined by Rietveld profile analysis. 23 Na NMR spectra of Na8Si46 and NaxSi136 samples reveals two peaks with large paramagnetic shifts (1600-2000 ppm) for each phase, associated with the presence of Na atoms in two different environments. High resolution electron microscopy reveals the clathrate structures of these samples, and allows classes of defects to be characterized.