Pronounced Compositional Variation

As we shall show below, two of the limiting factors in depth resolution and, therefore, the ability to determine interface widths are the temporal and spatial stability of the ion beam. One of the advantages of rastering the ion gun is to improve the spatial uniformity of the erosion rate. The most pronounced temporal variations occur during the first few seconds after the ion beam is turned on. But they are only important if changes in surface composition occur in the same time frame. Long term drifts in ion beam current or position are usually not critical in depth profiles. 

The petrological composition is important when considering the solvent extraction of prime coking coals but with lower rank British coals the variations in petrology are less pronounced. A more frequent cause of variations in extraction yield with low rank coals (CRC 802 and CRC 902) results from ageing. The reactivity of a coal decreases substantially as the coal becomes oxidised by exposure to the atmosphere (Table III). 

A series of works by Matsuda et al. composed perhaps the first systematic study to explore the physical foundation for such a mixing effect. Using PC/DME as a model system, they investigated the dependence of vapor pressure, dielectric constant, and viscosity on solvent composition, and they correlated these variations with ion conductions. It was found that the dielectric constant varied with solvent composition by following an almost linear relation, with slight positive deviations, while viscosity always showed a pronounced negative deviation from what a linear relation would predict (Figure 6b). For such binary solvent systems, approximate quantifications... 

The aerosol composition distribution. Figure 3, shows pronounced variation with particle size. The distribution has a distinct break in the 0.1 to 0.3 um size range. The larger particles account for the vast majority of the aerosol mass. 

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