Submitted to: Journal of Synchrotron Radiation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/1999
Publication Date: N/A
Interpretive Summary: Investigations of many samples require an aqueous environment as water surrounding the sample impacts its structure and properties. This is especially true of soil samples and the associated biological organisms. In the past, to view the details of soil microstructure, the samples were dried and pretreated, often with heavy metal powders. The soft x-ray microscopes offer a way to study these samples in hydrated form. These instruments provide excellent contrast for organics in samples when operated in the spectral region where water is relatives transparent. This paper describes the development and testing of a specimen chamber for use with soft x-ray microscopy of hydrated soil specimens and solutions. The instrument used was the scanning transmission x-ray microscope on the X1-A beam-line located at the National Synchrotron Light Source (NSLS) at the Brookhaven National Laboratory. It is possible to obtain images of the samples at a high resolution (less than 100 nm). The samples tested included hydrated soil samples interacting with molecules of polyacrylamide (PAM). PAM is used in many furrow irrigation systems to flocculate the soil during irrigation to reduce soil erosional losses. We were able to obtain a good image of the hydrated samples using this sample chamber. The chamber will allow scientists to study environmental samples in their normal hydrated state, allowing the study of soil-chemical- biological interactions.
Technical Abstract: Soft x-ray microscopes offer especially favorable contrast mechanisms for studying colloidal systems. The energy range of the water window between oxygen and carbon K absorption edges (543 and 284 eV) is of particular interest for studies on hydrated samples. In addition, x-ray absorption edges can be used to visualize and map compounds containing these elements versus other compounds. We used soft x-ray microscopy to image hydrated clays, to obtain contrast based on elemental composition (C, Ca), and to highlight C chemical states. Polyacrylamide is a flocculent that is added to irrigation water to reduce erosion and increase water efficiency. We used the scanning transmission x-ray microscope to visualize the flocculation of a KGa-1 kaolinite clay suspension at various concentrations of polyacrylamide. The results are in good agreement with the concentrations needed for field application, yet provide a very direct way of visualizing the effects of the flocculent. Clay-organic interactions have been studied in a system of an aqueous dispersion of 0.1-% sodium montmorillonite and 10 g/l trimethylammonium- polyethylenglycol 20000 molecular weight. Taking advantage of carbon absorption edge contrast, the details of this interaction and the structures of aggregates formed can be revealed. Other work includes looking at marine sediments. In the port of New York/New Jersey, a large fraction of marine sediment, that needs to be dredged from navigational channels is contaminated. This sediment has been imaged in a hydrated state near carbon absorption edge and carbonaceous material has been mapped. Current studies deal with analyzing the carbon contaminants in the contaminated sediment by C-XANES.