Corrosion features samples

The simultaneous multielement capability and low detection limits of an ICAP facilitates the analysis of mass-limited samples. Kniseley et al. (9) discussed this advantage with respect to small sample volumes of blood and serum. This feature was indispensable in the analysis of all specimens of human origin. Other areas where limited sample masses have been analyzed relate to materials testing, air particulates, and corrosion testing. Sample masses as low as a few milligrams have been successfully analyzed for 200-/xL volumes. 

Figure 15 gives a diagrammatic representation of a volumetric line which is used in connection with a high-temperature Calvet microcalorimeter 67). Other volumetric lines which have been described present the same general features (15, 68). In the case of corrosive gases or vapors, metallic systems may be used 69). In all cases, a sampling system (A in Fig. 15) permits the introduction of a small quantity of gas (or vapor) in a calibrated part of the volumetric line (between stopcocks Ri and Ro in Fig. 15) where its pressure Pi is measured (by means of the McLeod gage B in Fig. 15). The gas is then allowed to contact the adsorbent placed in the calorimeter cell C (by opening stopcock Ro in Fig. 15). The heat evolution is recorded and when it has come to completion, the final equi-...

Fig. 8. Scanning electron micrographs (SEM in secondary electrons mode) of the surface features of HT materials ground to 100-125 pm prior to (small micrographs) and after 10-day corrosion (large micrographs). Corroded sample P7 exhibits pits but almost no secondary mineral phases corroded sample P16 shows a dense cover of secondary minerals.

Some attractive features of radiography are access to interior difficult-to-reach portion, such as valves and pipes, the objects or sample covered with insulation can be tested, reference radiographs can be accessed, the nature and severity of the attack can be assessed with ease, in principle, pit depths can be obtained although laser profilometry is the preferred method in this regard. The main drawback of the method is the whole sample needs to be exposed. Some applications of the method are determination of flaws in weldments and castings to identify sites of initiation of crevice corrosion, valve... 

The choice of the technique used in monitoring or detection of corrosion depends upon many factors such as the size of the sample, the particular features of the defect, accessibility, sensitivity of the technique, the limitations of the techniques, knowledge and skills of the operator and the availability of the instrument. The following is a general guide for the application and suitability of the technique in the detection of discontinuity.52... 

By way of example. Tables 11 and 12 illustrate several important features of corrosion in SCWO systems using sample corrosion data for the commonly... 

Three-year corrosion films on galvanized steel from the New Jersey site did not possess solution-altered features on the skyward side. This was true also for the corresponding zinc samples. There were, however, substantial areas of uncorroded surface on both the skyward and groundward sides. While short-term corrosion rates are different between zinc and galvanized steel, in long-term exposures there are close parallels in the development of the weathered corrosion film on both materials. 

As the nature of the electrified interface dominates the kinetics of corrosive reactions, it is most desirable to measure, e.g., the drop in electrical potential across the interface, even where the interface is buried beneath a polymer layer and is therefore not accessible for conventional electrochemical techniques. The scanning Kelvin probe (SKP), which measures in principle the Volta potential difference (or contact potential difference) between the sample and a sensing probe (which may consist of a sharp wire composed of a conducting, stable phase such as graphite or gold) by the vibrating condenser method, is the only technique which allows the measurement of such data and therefore aU modern models which deal with electrochemical de-adhesion reactions are based on such techniques [1-8]. Recently, it has been apphed mainly for the measurement of electrode potentials at polymer/metal interfaces, especially polymer-coated metals such as iron, zinc, and aluminum alloys [9-15]. The principal features of a scanning Kelvin probe for corrosion studies are shown in Fig. 31.1. 

The ratios between the losses of helix and flat samples vary considerably often the helix specimens corrode more than twice as fast—this observation is in line with some other test results. No single feature seems to account for the differences, but the specimen geometry is an important factor high helix/flat corrosion ratios for zinc are often paralleled by similar high ratios... 

X-ray photoelectron spectroscopy (XPS) is a surface analytical approach that provides detailed chemical information from the top 1 to 10 nm of a sample surface. The surface is irradiated with an x-ray beam and the kinetic energy of the emitted electrons is analyzed. This technique is well established in the corrosion field because it has great utility to measure thin protective films and corrosion product layers. The latest technical developments in XPS instrumentation enhance the usefulness of the technique. One trend is a decreasing x-ray beam size. X-ray beams are much more difficult to focus than electron beams, which are used in many other analytical techniques. As a result, XPS has relatively poor lateral resolution. However, XPS tools now provide x-ray beams less than 10 micrometers in diameter, which allows for the analysis of surfaces on small microstructural features... 

A more detailed analysis of these survey results reveals some interesting features that relate to the terminology used in corrosion science and engineering. The results of interviews were anafyzed with Box-and-Whisker plots. These plots divide the data for each sample into four areas of equal fi quency. A box encloses the middle 50 %, and the median is drawn is a vertical... 

One of the most important factors to consider is the compatability of the cell optics with the sample, especially with an ATR sensing element (the IRE), because of their relative high cost. Accessories featuring diamond-based optics are now available, and these provide corrosion and chemical resistance for virtually any type of sample. 

Gas cells may be considered a special form of transmission cell. The difference is primarily in the construction of the body of the cell and its extended pathlength. In essence, a traditional gas cell (short path length) is a tube (with filling ports) with windows mounted and sealed at both ends. Like liquid cells, gas cells are available in demountable (removable windows) and permanent formats (bonded windows). Materials of construction can be important, especially if corrosive gases or vapors are studied. The most inexpensive cells feature glass tubular bodies, and these are ideal for many sample types. For a more rigid construction, cell bodies made from stainless steel, Monel, and Hastelloy C are available. 

The gold tubular glass samples tended to be covered with flaky black, presumably corrosion-related material that was mostly removable during sonication. Data for the eleven cleaned gold glass samples are presented in Table IX. The primary features of these data are the very low levels of K and Na, and the low levels of Ca and Cl. These features imply that the gold beads are lead-silica glasses. 

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