Chemistry Weekly Seminar - Arthur Situm, PhD Candidate

Title: 

The development of spectromicroscopy methods for the study of heterogeneous materials

Abstract:

Spectromicroscopy is the process by which chemical information is obtained from images. The objective of this thesis research was to develop X-ray spectromicroscopy methodologies that combine the elemental mapping of X-ray microprobe with the chemical information obtained from micro X-ray absorption near edge spectroscopy (µ-XANES) for the study of heterogeneous materials. Polymer coatings applied to rebar to mitigate corrosion prevent most analysis techniques from being able to characterize the rebar corrosion without removal of the coating. In this thesis, a nondestructive X-ray spectromicroscopy methodology was developed to study the corrosion of rebar without removing its polymer coating. Within the U mill tailings, mobility of U is controlled by the presence of dissolved bicarbonate. The concentration of bicarbonate is predicted to be controlled by the formation of calcium carbonates. However, the tailings are saturated with gypsum making calcium carbonates unidentifiable using bulk Ca K-edge XANES. This work further developes the X-ray spectromicroscopy methodology for identification of calcium carbonates. As a result, a variety of calcium carbonates were identified within the tailings, thus supporting the proposed geochemical model. Finally, a methodology developed to obtain U X-ray microprobe maps by deconvoluting the U X-ray fluorescence signal from overlapping signals will be disscussed.