Contamination, films

Fig. 2.13. Schematic diagram ofthe type of information obtainable from XPS spectra from an Fe-Cr alloy with oxide film underneath a contaminant film [2.57],...

More effort has probably been devoted to study of the corrosion and passivation properties of Fe-Cr-Ni alloys, e.g. stainless steel and other transition-metal alloys, than to any other metallic system [2.42, 2.44, 2.55, 2.56]. The type of spectral information obtainable from an Fe-Cr alloy of technical origin, carrying an oxide and contaminant film after corrosion, is shown schematically in Fig. 2.13 [2.57]. 

Rank the following polypropylene conversion processes in terms of their relative sensitivity to particulate contamination, film casting, injection molding or fiber spinning. 

When a clean metallic surface is exposed to ordinary ambient air, it acquires a contaminating film. Every common metal, with the exception of gold, reacts with the oxygen of the air to form an epitaxial film of oxide. In addition, there is a physically adsorbed film, comprised of oxygen, carbon dioxide, water vapor and other atmospheric constituents, that lies on top of the oxide layer. Consequently the process of "cleaning" surfaces for friction studies by abrasion, polishing, water-washing... 

Another explanation for the initial period of no wear is that the polyimide and ball surfaces were contaminated by a film. This film caused low friction and surface stresses below that required for immediate wear particle generation. The initial period is the time during which the film is worn away resulting in an increase in adhesion, increase in surface stress, and subsequent wear particle formation. Obviously, both fatigue and contaminant film removal could be operative during the initiation period. Experiments with carefully controlled environments and surface cleaning procedures would be necessary to discriminate between these two explanations. 

Spots on the film Contaminated film cassette The gel was not properly equilibrated with the scintillator (could not swim freely, not enough scintillator) Gel must not stick to the floor of the tub, allow to swim freely In 5 times more scintillator than gel. 

Bales weighing 600-800 lb, collected by commercial haulers, film-generating business, or the solid-wastes-handling industry, are first fed into a breaker-shredder. The shredded material then passes over a vibratory conveyor or through metal-detection systems to remove ferrous and nonferrous contaminants. Film is next sent to a sedimentation tank for removal of rocks or dirt before going into the granulator... 

Hoshi et al. studied their films by TEM as well. From the corresponding electron diffraction patterns they inferred that phase separation had taken place, involving the formation of a nitride or oxide of part of the Gd. Both the oxygen-contaminated film and the nitrogen-contaminated film had essentially the same microstructure and this microstructure was not composed of columns usually obtained by means of sputtering. From these results the authors conclude that shape anisotropy associated with structural or compositional fluctuations apparently contributes little to the perpendicular anisotropy in Gd-Co films. 

Figure 4.2. Model of polished metal surfaces with roi ness and contaminant film.

A jump towards the surface is even more likely when contamination is present, because then the probe and surface are joined by a liquid layer and surface tension pulls them together. In this case, the probe jumps to a position where there is a net attractive force, but the tip is in repulsive contact with the surface. Operating the microscope in a good vacuum, in dry gas, or in a liquid reduces or eliminates the effects of contamination. Water is often quoted as the liquid, but if there is an oily contamination film on a hydrophobic surface, iso-propanol or other organic solvents may be better than water. The primary aim of this is to have lower forces on the surface. Detailed interpretation of the measured forces is complex [207], and contamination layers makes it even more difficult. 

A further interfacial factor can be the presence of non adsorbable or non desorbable contaminating films (as previously mentioned above) at the interface. Such materials can be oils, fatty acids, plasticisers from the rubber and metal processing oils from inadequately cleaned metal components. Some of these lubricants can be absorbed by the adhesive if it is solvent-based but in the case of the new waterborne rubber to metal systems this absorption cannot take place, for the systems are neither miscible or compatible with oils. These new waterborne systems have a critical tolerance level for surface contamination of the metal and if this is exceeded then wetting out of the metal by the adhesive will not, at the worst be possible, or at the best complete. 

The mechanical energy expended in rubbing an adhesive into a metal surface has been studied and correlated with measured increases in bond strength.8) jt is presumed that the likely mechanism is an increase in the displacement of contaminant film from the adherend surface. If this explanation is correct then durability could also be improved, since the effect of a potential weak boundary layer condition at the interface should be diminished. It is doubtful, however, that there would be much improvement in resistance to severe service conditions, such as a combination of significant stressing and water-soaking conditions. 

Metallic or contaminated films or fine particles Remarks about the fee phase 133... 

Polymerization, electron beam EB polymerization is a slow irradiating process. Monomeric materials that have been irradiated to produce plastic films include silicone, butadiene, styrene, methyl methacrylate, and epoxy. However the lack of selectivity of this energy source can result in contamination. Film properties can be tailored by varying the acceleration voltage. >coating, vacuum... 

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