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The Development of Spectromicroscopy Methods for the Study of Heterogeneous Materials

Webinar Presented By:  PDF Arthur Situm, Chemical Engineering and Applied Chemistry, University of Toronto

Speaker Bio:  Dr. Situm obtained his Bachelors in Honors Chemistry in 2014 and his Masters in Chemistry in 2016 both from Laurier under my supervision. Both his undergraduate and master's thesis were on the topic of The role of organic matter in the surface chemistry of arsenic compounds on iron−(oxyhydr)oxides studied by ATR-FTIR. He recently completed his PhD in chemistry at the University of Saskatchewan under the supervision of Andrew Grosvenor where he studied polymer steel corrosion and uranium mill waste at the Canadian Light Source. He has now started a postdoctoral fellowship at Western University under the supervision of Prof Jamie Noel on the corrosion of used nuclear fuel containers and has been awarded the NSERC PDF award to support this research. He will now be presenting on this PhD thesis research on 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 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. The two types of heterogeneous materials studied in this thesis were polymer coated rebar and U mill tailings. 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. Removal of polymer coatings prevents further experimentation using the rebar and potentially damages the corrosion being studied. In this thesis, a nondestructive X-ray spectromicroscopy methodology was developed to study the corrosion of polymer coated rebar without removing the polymer coating. This has been achieved by utilizing the higher absorption cross-section of Fe metal when the excitation energy is 7115 eV compared to Fe corrosion products. Within the tailings, mobility of U is controlled by the presence of dissolved bicarbonate within the tailings porewater which may form soluble uranyl carbonate complexes. The maximum concentration of bicarbonate in the tailings porewater is predicted to be controlled by the formation of calcium carbonates, thus limiting the formation of soluble uranyl carbonate complexes. However, the tailings are saturated with gypsum, making calcium carbonates within the tailings unidentifiable using bulk Ca K-edge XANES. To overcome this, additional data analysis procedures were incorporated into the original X-ray spectromicroscopy methodology to identify the calcium carbonates. As a result, a variety of calcium carbonates were identified within the tailings, thus supporting the proposed geochemical model. Additionally, the U concentration within the tailings is low, giving rise to bulk U M5-edge XANES spectra with low intensity and iii poor signal to noise ratios. The final part of this thesis outlines a methodology developed to obtain U elemental maps from X-ray microprobe by deconvoluting the U X-ray fluorescence signal from overlapping signals. These U maps allow for the collection of U M5-edge μ-XANES spectra with significantly higher signal to noise ratios than bulk U M5-edge XANES.

Date and Time:  March 5, 2021 | 3:30 p.m.


Access through MyLS:  Chemistry and Biochemistry Seminar Series , passcode:  7u882y

If you are outside of the Department of Chemistry and Biochemistry, please contact the seminar host, Hind Al-Abadleh.

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