Search

A prominent feature of soil colloids is their huge specific surface. It determines colloidal properties such as adsorption capacity or diffusion. The colloidal interactions differ significantly from the behavior of the same materials in a bulk system. Interactions in the colloidal regime are crucial, for example, for the transport and release of nutrients and toxicants in soils, which then influences directly the growth of plants. However, there is still a need for more analytical resources to study those interactions. To reveal the correlation of the particular trace elements and their distribution in correlation to colloidal interactions as well as changing pH values, experiments at the hard x-ray fluorescence microprobe at beamline 2-ID-E of the Advanced Photon Source (APS), were performed with colloidal clay and soil samples in an aqueous environment as naturally relevant. To obtain further spatial information, stereo imaging has been used. To study the dynamical behavior of these colloidal suspensions at changing pH, a wet sample chamber allowing in situ manipulation was developed and utilized. [ABSTRACT FROM AUTHOR]

X-ray microscopy and scattering experiments give different experimental results when determining the fractal dimension of colloidal clusters. A two dimensional simulation model is presented to describe reorganization of clusters during the aggregation process. Considering this reorganization gives a rapidly increasing fractal dimension from d=1.53 to d=1.61. This result implies that the fractal dimension of the clusters is mainly affected by reorganization of small sub clusters. [ABSTRACT FROM AUTHOR]

Soil is a part of the environment where colloidal systems play an important role when it comes to the description of its properties. A great variety of chemical reactions within these systems occur in an aqueous phase. Due to its ability to image specimen directly in their natural aqueous environment, X-ray microscopy is very suitable tool for the study of these systems. Man-made contamination of soils, especially organic contaminations, can be removed with thermal clean-up techniques. These techniques influence strongly the shape of the colloidal systems within the treated soils. X-ray microscopy studies of an agriculturally used soil and a forest soil give examples of this influence. [ABSTRACT FROM AUTHOR]

A new scanning transmission X-ray microscope (STXM) is under construction and will be operated at the undulator U41 of the BESSY II storage ring, In the monochromator without entrance or exit slits, a plane grating with variable line density is used. A spectral resolution of 2200 to 6500 is expected in the energy range of 680 eV to 200 eV. The sample is located in air so it can be exchanged easily. The photon rate in the focus will be of the order of 10[sup 9] / s at a monochromaticity of 3000. A pnCCD capable of handling this rate will be used as a detector. [ABSTRACT FROM AUTHOR]

The influence of organic matter, the humic substances, on the precipitation behavior of the iron in groundwater aquifers was studied. Size and structure of these associations are determined using fractal geometry. The humic substances were characterized spectroscopically. For differentiation of organic and inorganic substances, the contrast at the carbon Κ-absorption edge was used. Spectra were taken at different spots of the samples to investigate, whether there are differences in the spectra with and without iron. [ABSTRACT FROM AUTHOR]

Studying properties of natural colloidal systems, one major issue is the question, whether the shape of the associations formed can be described morphometrically. Therefore, X-ray microscopy experiments have been performed with hematite particles, which have been forced to coagulate by adding increasing amounts of sodium sulfate as a coagulation agent. An important figure is the critical coagulation concentration c.c.c., where the repulsive potential around these colloidal particles is matched in its range with the attractive van der Waals potential. To calculate the fractal dimension of the associations in the X-ray micrographs is one way to characterize the structures formed. The method used here is the box-counting algorithm. The calculated box-counting dimensions show that the associations have an increasingly denser shape when crossing the c.c.c.. [ABSTRACT FROM AUTHOR]

The undulator U41 at BESSY II will be used as source for X-ray microscopes. An overview of the X-ray microscopy area is presented. After finishing the construction phase a transmission X-ray microscope, a scanning transmission X-ray microscope and an X-ray test chamber will be available. The transmission X-ray microscope will allow investigations with high lateral resolution at moderate energy resolution while the scanning transmission X-ray microscope will allow high energy resolution at moderate lateral resolution of the same specimen. [ABSTRACT FROM AUTHOR]