X-ray photoelectron spectroscopy (XPS) can provide a quantitative analysis of the surface and determine the chemical state of elements present. However, until recently the spatial resolution has not been adequate to analyse small particles. As a result, Auger electron spectroscopy has been used to obtain elemental information where good spatial resolution is required. Analysis of grain boundary surfaces has therefore been restricted to this technique, with the result that no chemical-state information has been obtained relating to the elements present on the grain boundary. This paper describes results in which grain boundary surfaces exposed in an imaging XPS instrument have been analysed using XPS. In particular, tin and phosphorus are shown to segregate to the grain boundary surface in the elemental state.
Sorption / Cs + / Ba 2+ / Chlorite / Illite / ToF-SIMS / XPS / XRDSummary. The sorption behavior of Cs + , and Ba 2+ on natural clay was investigated using ToF-SIMS, XPS, and XRD. The natural clay was composed mainly of chlorite and illite in addition to quartz and calcite. Depth profiling up to 70 Å was performed at 10 Å steps utilizing ToF-SIMS to study the amount of sorbed Cs + and Ba 2+ as a function of depth in the clay matrix. The results suggest that Cs + and Ba 2+ ions were sorbed primarily by ion exchange coupled with hydrolytic sorption. According to ToF-SIMS and XPS results, the total sorbed amount of Ba 2+ was larger than that of Cs + . Quantitative determination of the primary cations within the analyzed clay before and after sorption indicated that for Ba 2+ sorption, Ca 2+ , Mg 2+ and for Cs + sorption Ca 2+ , K + were the major exchanging ions. The XRD spectra of Ba-sorbed clay contained new peaks that were identified as BaCO 3 .
One of the main questions regarding protein adsorption is about the reversibility of the adsorption process. To get a deeper understanding of this, adsorption of ferritin on Au was studied by quartz crystal microbalance and the pH of the buffer was changed in situ between two values that favour adsorption by different amounts. We found that although some ferritin desorbs from Au, the desorption is incomplete. When the desorption reached a constant value, we returned to the original conditions and investigated the readsorption. Our experiments show that the adsorption of ferritin onto Au is a partly reversible process. We found that for different initial ferritin coverages the proportion of ferritin that had been subsequently desorbed was approximately constant.
Reagent-based selective separations of minerals are of great industrial importance. The basis of these separations is the competitive differential adsorption of the reagent onto a number of minerals. An X-ray photoelectron spectroscopic (XPS) study of the adsorption of polyacrylamide onto kaolin, feldspar and quartz is described. Initial data confirmed the utility of XPS for the study of polyacrylamide adsorption onto silica glass slides. Further results indicated the utility of the technique for the direct measurement of adsorption of polyacrylamide onto individual aliquots of kaolin, feldspar and quartz. Adsorption was relatively greatest onto kaolin. Feldspar displayed less adsorption and quartz very little. An imaging method was used to characterize, at least relatively, the competitive adsorption of polyacrylamide onto kaolin in the presence of mixtures of kaolin and quartz. This is a potential new technique for study of competitive adsorption.
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