Compositional analysis precipitates

However, for the past 30 years fractional separation has been the basis for most asphalt composition analysis (Fig. 10). The separation methods that have been used divide asphalt into operationally defined fractions. Four types of asphalt separation procedures are now in use ( /) chemical precipitation in which / -pentane separation of asphaltenes is foUowed by chemical precipitation of other fractions with sulfuric acid of increasing concentration (ASTM D2006) (2) solvent fractionation separation of an "asphaltene" fraction by the use of 1-butanol foUowed by dissolution of the 1-butanol solubles in... 

In compositional analysis of very small precipitates, or in interface segregation studies, using a probe-hole type atom-probe, one is always faced with the fact that the probe-hole may cover both the matrix and the precipitate phases, or the interface as well as the matrix. Thus any abrupt compositional changes will be smeared out by the size of the probe-hole and also by the effect of ion trajectories. A similar uncertainty seems to exist in the compositional analysis of nitride platelets formed in nitrided Fe-3 at.% Mo alloy, aged between 450 and 600°C, where Wagner ... 

Typically, colloidal suspensions are deposited on polycarbonate filters immediately following sampling to reduce post-collection precipitation or aggregation artifacts and mimic the operational procedures used to define dissolved and particulate sample components. Obviously, a well-dispersed dilute sample should be used to avoid artifactual particle overlap. Filter sections are then mounted on SEM stubs and carbon or metal coated (Au/Pd) for compositional analysis and micrographic imaging, respectively. The tedious nature of operator controlled analysis of particulate samples in the SEM and the TEM has often precluded the acquisition of statistically valid information regarding suspension composition. 

The assumption that montmorillonite of reported composition is being produced and is the only authigenic phase is probably only an approximation. The composition may be in error or may vary areally within Rainier Mesa as a result of areal variations in water quality. Although no zeolites or other clay minerals were reported in the bulk of the Paintbrush Tuff, very small amounts may remain undetected by either x-ray diffraction analysis or thin-sectlon petrography and may affect the aqueous composition by precipitation or by ion exchange. 

Figure 7. a) Mean annual oxygen isotope composition of precipitation (i5 Op) history derived from isotope analysis of fossil wood cellulose near Brampton, Ontario, b) Hamilton Harbour bulk organic C/N ratio and cellulo.se-inferred lake water 6 0 profiles. Also shown is the i Op record for southern Ontario from... 

Pagano, J.J., Thouvenel-Romans, S., and Steinbock, O. (2007) Compositional analysis of copper-silica precipitation tubes. Phys. Chem. Chem. Phys., 9, 110-116. 

Analysis of flowback samples is important for observation of sludge, emulsion, solids production, and related problems. Compositional analysis of spent add (see chapter 16) can shed light on problems, espedally precipitation of add reaction products, and can be used to optimize future treatment design. 

A precipitation gravimetric analysis must have several important attributes. Eirst, the precipitate must be of low solubility, high purity, and of known composition if its mass is to accurately reflect the analyte s mass. Second, the precipitate must be in a form that is easy to separate from the reaction mixture. The theoretical and experimental details of precipitation gravimetry are reviewed in this section. 

Asphaltenes seem to be relatively constant in composition in residual asphalts, despite the source, as deterrnined by elemental analysis (6). Deterrnination of asphaltenes is relatively standard, and the fractions are termed / -pentane, / -hexane, / -heptane, or naphtha-insoluble, depending upon the precipitant used (5,6,49). After the asphaltenes are removed, resinous fractions are removed from the maltenes-petrolenes usually by adsorption on activated gels or clays. Recovery of the resin fraction by desorbtion is usually nearly quantitative. 

Precipitated K—salt crystals are carefully filtrated and washed so as to separate them from the mother solution. Drying of filtrated K-salt is also a very delicate and important process that must be performed under conditions that avoid hydrolysis of the material. Potassium heptafluorotantalate is sensitive to water, basic compounds and alcohols, especially at elevated temperatures. The main product of K-salt hydrolysis is Marignac s salt. For a long time it was believed that the composition of Marignac s salt is K/Ta Fg. However, X-ray crystal structure analysis and precise chemical analysis of the... 

For example, consider the chemical composition of a very old crystal of pitchblende, U308. We may presume that this crystal was formed at a time when chemical conditions for its formation were favorable. For example, it may have precipitated from molten rock during cooling. The resulting crystals tend to exclude impurities. Yet, careful analysis shows that every deposit of pitchblende contains a small amount of lead. This lead has accumulated in the crystal, beginning at the moment the pure crystal was formed, due to the radioactive decay of the uranium. 

Now consider the simultaneous evolution of and c)D. Suppose an air mass having initial compositions 3, = 0 cools and precipitates, always as an equilibrium process. According to the preceding analysis, measurements of both isotopic ratios in precipitation will plot on a curve with a slope approximately given by... 

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