Use of micro-proton elastic scattering analysis to determine water content in geological powders

Hydrogen in the form of water (H2O), hydroxyl anion (OH−) and H2 is a pervasive component in minerals, affecting geochemical processes from the surface of the earth to its deep interior and the geophysical and rheological properties of the rock. To investigate the application of ion beam techniques to the measurement of structural water (OH− and H2O), purified mineral separates, volcanic glass and synthetic borosilicate glass with known total structural water contents were selected. Mineral and glass particles <50 μm in diameter and thickness, were deposited onto Teflon filters and scanned with a focussed 2.5 MeV proton beam. Hydrogen was measured using proton elastic scattering analysis and converted to total H2O. Heavier elements were detected via Proton-Induced X-ray Emission (PIXE). Measurements were conducted in high vacuum to detect bound water only. The water content measurements for the minerals measured showed very good agreement with bulk water measurements and literature values. This method can be used successfully to noninvasively determine the hydrogen content of individual mineral particles with >1% total water contents.