Surface cleanliness measurement

In the first set of measurements the rate of carbon build-up on a Ni(lOO) surface was measured at various temperatures as follows (1) surface cleanliness was established by AES (2) the sample was retracted into the reaction chamber and exposed to several torr of CO for various times at a given temperature (3) after evacuation the sample was transferred to the analysis chamber and (4) the AES spectra of C and Ni were measured. Two features of this study are noteworthy. First, two kinds of carbon forms are evident - a carbidic type which occurs at temperatures < 650 K and a graphite type at temperatures > 650 K. The carbide form saturates at 0.5 monolayers. Second, the carbon formation data from CO disproportionation indicates a rate equivalent to that observed for methane formation in a H2/CO mixture. Therefore, the surface carbon route to product is sufficiently rapid to account for methane production with the assumption that kinetic limitations are not imposed by the hydrogenation of this surface carbon. 

In many areas of applied surface thermodynamics, measurement of contact angles plays an important role. The range of applications of contact angle measurement is remarkable. It can be used as a simple tool to assess, for example, the cleanliness of the surfaces, or it can be a highly sensitive scientific measurement aimed at obtaining information on the solid surface tension and the... 

In this report, these concepts are applied to real proteins to collagen, an important structural material in tendons, bones, teeth, and skin, and to gelatin, the denatured product of collagen that is so important industrially. These materials are complex because of their 18 different, component amino acid side chains in addition, they present experimental difficulties because of their water solubility— they cannot be washed (e.g., with an aqueous detergent) to assure surface cleanliness. Furthermore, they are often of unknown purity. They do have the common polyamide backbone, and it is possible to transform the molecular configuration. The data are indicative of the potential utility of contact angle measurements of important, natural materials. No claim is made for adequate attention to the complex biochemistry of these materials. 

The electrocapillary curve of a solid metal electrode is more difficult to measure than that of a liquid electrode, because of problems of surface cleanliness. The most widely used approach has been the bending-beam method, which was originally developed by Fredlein et al. [28] using large samples. More recently Raiteri and Butt [29] have used gold electrodes deposited on an AFM cantilever to record electrocapillary curves. 

Impurity adatoms, such as H, N and O, have a dramatic influence on measured accommodation coefficients for example, a monolayer of oxygen adatoms on polycrystalline tungsten raises the ac for helium from 0.02 for a clean surface to 0.6. Roberts [388] and co-workers made use of this sensitivity to the presence of adsorbates to determine sticking probabilities for reactive gases on tungsten. West and Somorjai [389] have used the extent of He elastic scattering as a sensitive measure of surface cleanliness. 

The methods suitable for control of surface cleanliness are mainly those discussed in Section 3.1.2. Compositional changes on and near the surface of glass (i.e. to a depth of about 20 A) can be measured with Auger electron spectroscopy (AES), electron spectroscopy for chemical analysis (ESCA), ion-scattering spectroscopy... 

A more universal test is the probe test, in which the end of a cylinder of standard diameter is brought lightly into contact with the film for a very short time and the force required to separate it from the surface is measured. Similar in principle is the loop tack test, in which a loop of coated film is lowered onto a steel plate, making contact under its own weight, and the force required to withdraw the plate is then measured. All of these tests are markedly affected by the cleanliness of the ball, probe, or plate. Figure 4 illustrates the loop tack test. 

Let me narrate an example that resulted in the disbondment of almost 500 km of pipeline, coated with 3LPE, just because no care was taken in measuring the surface cleanliness. A few tens of parts per million of salt remain after the surface preparation resulted in the disbondment (Figure 8.2). 

Surface release properties A smooth surface tends to discourage the adhesion of cohesive, damp, wet, or fatty solids, although when the avoidance of such behaviour is important, the surface cohesion of optional surfaces should be measured by tests. Surface cohesion is shown on a graph, whereby the force promoting shp is plotted versus the normal load. The intercept on the slip force axis shows the measure of surface cohesion. A bright, polished surface is not normally required for surface cleanliness or to... 

The level of surface cleanliness may also be evaluated by measuring the surface-insulation resistance (SIR) of a separate test pattern. The SIR test sample consists of an interdigitated comb pattern of conductor lines and spacings on a printed-circuit laminate representative of the actual circuit. The IPC B-25 or IPC B-24 test patterns (Fig. 4.3) are standard in the industry to evaluate the degree of cleanliness of a surface. If the test pattern is well cleaned and no ionic residues remain, the insulation resistances between conductor lines will be 10 ohms or greater and will not drop appreciably under moist ambients. If residues remain, leakage currents... 

Furthermore, the work function is a parameter which is highly sensitive to the state of the surface of a solid [79,80]. Experimental determinations of the of a surface can therefore vary by several tenths of an eV, even in similar experimental conditions, and can also depend on which measurement technique is employed. For example, although gold work function is usually reported to be 5.1 eV in UHV, it has been demonstrated that it can be as low as 4.2 eV and as high as 5.4 eV and a range of values in between depending on the surface cleanliness and ambient conditions [79,81-83]. Similar variations in the barrier height, ate thus expected. 

The contamination of tower surfaces with aggressive chemicals can lead to enhanced corrosion and deterioration of protective coatings. Although the methods of detection and deteimination of surface contamination are not standardized, several test methods [7] are accepted by the industry. Surface contamination analysis kits are available [8] to measure pH, chlorides (detection limit 40 ppm) and soluble ferrous ions (detection limit approximately 3 ppm). In most cases, these detection limits are sufficient to establish aggressivity of the operating enviroiunent and surface cleanliness before painting. 

Electrochemical reactions are heterogeneous in nature with the reaction kinetics being controlled by the properties of the electrode-electrolyte interface and the concentration of reactant available at this interface. Therefore, the physical, chemical, and electronic properties of the electrode surface are of paramount importance. Several factors will influence the electron-transfer kinetics for a redox system (i) type of electrode material, (ii) surface cleanliness, (iii) surface microstructure, (iv) surface chemistry, and (v) electronic properties (e.g., charge carrier mobility and concentration, which can be potential dependent for some semiconducting electrodes). Of course, if the solid is not a good electrical conductor (low charge carrier mobility and/or carrier concentration), then the current flow will be limited and the material will have drawbacks for electrochemical measurements. With the exception... 

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