Thin surface films

Many current designs use far more material than is necessary, or use potentially scarce materials where the more plentiful would serve. Often, for example, it is a surface property (e.g. low friction, or high corrosion resistance) which is wanted then a thin surface film of the rare material bonded to a cheap plentiful substrate can replace the bulk use of a scarcer material. Another way of coping with shortages is by... 

Included in this class of thin surface films are oxides, corrosion, contamination, and deposited layers. Although the presence of the bulk specimen results in increased... 

The corrosion resistance of lead is due to the formation of a thin surface film of an insoluble lead salt that protects the metal from sulfuric acid and related compounds of any strength at ordinary temperatures. Even when (he temperature increases to nearly 100°C the rates of corrosion are still low. However, strong, hot sulfuric acid attacks lead rapidly, especially if the acid is flowing. 

Because of its relatively low melting point (232 °C) and good resistance to oxidation, tin is used to provide protective coatings on metals such as iron that oxidize more readily. Tin cans are iron cans dipped in molten tin to provide a thin surface film of tin. Traditional metalsmiths use a similar process, coating copperware with a thin film of tin. 

For this reason, the dissolution of hydrous oxides does not require a high energy of activation. If hydrous oxides are dehydrated, they become dry oxides, which therefore acquire higher resistance to anodic dissolution. The most straightforward way to obtain dry oxides is to subject hydrous oxides to thermal treatments or better to prepare them as thin surface films by a non-electrochemical technique (thermal decomposition, chemical vapor deposition, reactive sputtering, etc.). 

On the influence of thin surface films on the evaporation of water. J. Phys. Chem., 29 1585-1588. 

The experimental aspects of ex situ FUR spectroscopic studies of sensitive electrodes (e.g., Li and Ca surfaces) using a purged spectrometer (not in a glove box) have been described in detail in Refs. 36-38, 92, and 93. Briefly, it is possible to analyze thin surface films on active metal, using a reflectance mode, while the active surface is in contact with a KBr or NaCl polished window. In Refs. 37 and 38, a possible organization of the measurement chamber of an FTIR spectrometer for such measurements is described. It should be noted, however, that the performance of such measurements when the spectrometer is placed in the glove box is much more elegant and easier. 

ATR Techniques for the Study of Thin Surface Films, presented at the Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, 1975. 

On the other hand, under low operating stresses the coatings behaved as relatively hard films. Only a thin surface film would have been re oriented, with little consolidation. With the low applied contact stress there would be little tendency for the underlayer to distort, and the thin oriented film would itself be more flexible. The surface would therefore wear gradually, and be replaced from the underlaying... 

Different types of reflectance spectroscopy depend upon the reflecting behavior of the radiation on the solid. Fig. 8 illustrates various categories used to distinguish techniques for reflecting radiation off solids. Specular reflection spectroscopy is used to measure the reflectance spectrum of a smooth, glossy surface. In reflection-absorption spectroscopy, the radiation passes through a thin surface film on a reflective... 

In addition to the electrochemical techniques, many insitu and exsitu surface analytical techniques are used in studies of silicon electrodes, such as ellipsometry for determining thin surface film thickness, ° infrared spectroscopy for surface adsorption, 260,424 surface composition, and for... 

Use To form thin surface films for protection of aluminum coatings, optical parts, mirrors, dielectrics, or insulators. 

The recorded chemiluminescence originated from only a thin surface film. The thickness of this film depends on the extent of self-absorption of the emitted radiation and remains unknown at this time. The pseudo-first-order rate of thermo-oxidative reactions responsible for the chemiluminescence is not limited by oxygen concentration. The applied stress decreases the activation energy for thermooxidative reactions, resulting in the observed chemiluminescence increase. As stress-activated bonds in the surface film react, what can be called surface stress relaxation occurs resulting in the observed SCL decrease. 

Fig. 1. Optical set for total internal reflection fluorescence spectroscopy. 6 incident angle of an excitation laser beam. S-film thin surface film. B-film thick bulk film.

Fig. 10. Schematic diagram of a microcomputer-controlled system of nanosecond attenuated total reflection UV-visible absorption spectroscopy. Inserted figure is an optical set of the sample where a bilayer model system consists of a thin surface-film and a thick bulk-film.

Boundary lubrication is characterized by film thicknesses of < 0.025 pm, which is less than the height of the asperity contacts. Mixed film, or EHD boundary lubrication, occurs at the transition from boundary to EHD lubrication. For comparison, the relative sizes of various components of a wear contact are provided in Figure 4.3.9 Because the solids are not separated by a lubricant, fluid film effects are negligible and there is considerable asperity contact. The contact lubrication mechanism is dominated by the physical and chemical properties of thin surface films of molecular proportions. The properties of the bulk lubricant are of minor importance, and the friction coefficient is essentially independent of fluid viscosity. The frictional characteristics are determined by the properties of the solids and the lubricant film at the common interfaces. 

Lubricity additives are used to compensate for the poor lubricity of severely hydrotreated diesel fuels. They contain a polar group that is attracted to metal surfaces, causing the additive to form a thin surface film. The film acts as a boundary lubricant when two metal surfaces come in contact. Two additive chemicals, fatty acids and esters, are typically used for this purpose. 

Stage 4 Migration of Ca2+ and HP042- ions through the silica network and formation of a Ca0-P205-rich thin surface film that subsequently transforms into an amorphous layer by incorporation of soluble calcium and phosphate ions from solution (Kim, Clark and Hench, 1989)... 

The qualitative application of photocurrent spectroscopy to bulk semiconductor electrodes is well established. This chapter is therefore largely concerned with quantitative aspects of the technique and particular emphasis is placed on the investigation of thin surface films on metal electrodes. 

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