Benefits of X-Ray Spectrum Simulation at low Energies

 There are particular benefits in spectrum simulation for the interpretation of characteristic X-ray peaks below about 2 keV in energy, where peak overlaps, a sloping background and changing detector efficiency make it difficult to measure true peak intensities. Despite these difficulties, we have shown that a useful accuracy of simulation is possible without major revision of the existing theory, allowing the electron microprobe user to compare on-line a measured spectrum with one synthesised from an assumed sample composition. As part of a wider study, we have used a database of X-ray spectra from 150 samples of known composition to confirm the accuracy of simulation over the energy range from 0.28–1.9 keV, finding an RMS error of better than 8%. The database included 181 Kα, Lα and Mα peaks from elements of atomic number 6–77, excited by beam voltages from 5–30 kV. Central to the method is the use of the ratio of (Peak Intensity)/(Total Background Intensity), which allows spectra to be compared from instruments of differing collection efficiency, thereby easing the collection of data over a wide range of conditions. Examples are given to illustrate the use of the simulator in helping to choose the best conditions for analysis, and as an aid in interpreting the spectra so obtained. Both modes of operation are iterative in nature and require a fast and accurate simulator that is easy to use. Further development will be guided by experience in its use.     

Effect of pH and salt concentration on the phase inversion of particle-stabilized foams

The effect of pH and salt concentration on the phase inversion of silica particle-stabilized foams is presented. Inversion from a water-in-air powder to an air-in-water foam can be achieved by increasing the pH of the aqueous phase. By contrast, an increase in the salt concentration causes a nonfoaming aqueous dispersion to foam. The results are rationalized in terms of changes in the hydrophobicity of the solid surfaces, probed by measurement of the contact angles of water drops on hydrophobized glass slides in air.     

Correction procedures in electron probe microanalysis of bulk samples

In recent years many of the advances in quantitative microprobe analysis have come from the improved ability to model the complex physics in the computer. This has enabled the accuracy of normal bulk analysis to be improved-right down to the very light elements as far as boron-and has extended the technique to the analysis of multiple thin films and layered samples. It has also allowed the user to shortcut the use of standards, though at the cost of somewhat reduced accuracy. Thus the analyst has come to rely more and more on correction procedures of increasing complexity, yet at the same time must understand their limitations. It is likely that in future the computer itself will be able to accumulate the best practice of expert users, advising the newcomer how these procedures can be best applied and where they are most likely to be in error.