Final Surface Preparation

The final aim is to have an electrochemical interphase chemically clean both on the solution side (water, chemicals, gas) and on the metal side (no oxide, no sulfide, no traces of the polishing solutions), and physically well-defined at the outermost layer, or layers, of atoms being as they are in the bulk metal in a plane parallel to the surface. We shall discuss two examples. 

It must be pointed out that oxides formed on silver cannot be reduced electrochemically. 

For each metal and each solvent a final preparation of the face has to be adopted. In some cases this final surface preparation is at the same time a check of the quality of the electrochemical interphase. 

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The painting procedure for other metal surfaces, although similar, the process of pre-treatment for cast iron components or non-ferrous metals, such as aluminium and copper, may need more care. The process of pre-treatment in such cases may vary slightly than for MS, as noted below. Such surfaces may require a change in the type of chemicals, their concentration and duration of treatment. The final surface preparation and painting procedure, however, will remain the same for all. 

Electrochemical or chemical polishing, whatever is the rinsing procedure, leaves traces of chemicals at the surface (cyanide in the case of gold or silver, for instance). These polishing stages are followed either by annealing or by one of the final surface preparations (see Section IV.4). 

Although not of primary concern in this review a number of experimenters have developed information on the oxidation rates of amorphous and polycrystalline films of germanium. While there is some disagreement on the role of porosity in the oxidation rate of such films, (17,18) the kinetics of the reaction appear to be strongly dependent on the morphology of the films and the ambient atmospheres to which they are initially exposed. Based on that information it would appear that implant areas should be annealed in situ or at least removed from vacuum to a controlled environment until final surface preparation is affected. This is particularly true of photovoltaic and photo-conductive devices where the uniformity of oxide, interface moisture content, uptake of carbon complexes etc. strongly affect the surface recombination currents and hence the device performance (77). 

Because adhesives bond by surface attachment, the physical and chemical condition of the adherends surface is extremely important for good joint performance and durability. Immediately after preparation, all surfaces undergo an inactivation process. To achieve optimal adhesion it is recommended that no more time than necessary should be allowed to elapse between final surface preparation and bonding. The prepared surfaces should be kept covered with... 

The final section in this volume deals with applications of adhesion science. The applications described include methods by which durable adhesive bonds can be manufactured by the use of appropriate surface preparation (Davis and Venables) to unique methods for composite repair (Lopata et al.) Adhesive applications find their way into the generation of wood products (Dunky and Pizzi) and also find their way into the construction of commercial and military aircraft (Pate). The chapter by Spotnitz et al. shows that adhesion science finds its way into the life sciences in their discussion of tissue adhesives. 

University of Arkansas and Louisiana State University. In-Situ Methods for the Control of Emissions from Surface Impoundments and Landfills. Draft Final Report. Prepared for U.S. Environmental Protection Agency. Contract No. CR810856. June 1985. pp. 95. 

Paint is the most widely used protective coating for steelwork and normally acts as a barrier between the metal and environment. The choice of type of paint and the final thickness required depends on the conditions of service, and the more severe the conditions the thicker and more resistant the paint film needs to be. Also the more sophisticated the paint system the more demanding is the surface preparation required. 

Finally, in considering coating it must never be forgotten that surface preparation is an essential part of the process and must also be considered by the designer. 

Primers can be used to protect both treated metal and nonmetal substrates after surface treatment. The use of a primer as a shop protectant may increase production costs, but it may also provide enhanced and more consistent adhesive strength. The use of a primer greatly increases production flexibility in bonding operations. Usually primer application can be incorporated as the final step in the surface preparation process. The primer is applied as soon as possible after surface preparation and usually no more than a few hours later. The actual application of the adhesive may then be delayed significantly. 

The substrate should then be washed in tap water and rinsed with distilled water. The final step in the process is an oven-dry of 10 min at 121 to 177°C.26 Several other surface preparation procedures for beryllium have been reported to have merit. Epoxy and epoxy hybrid adhesives have been found to provide high strengths on sulfuric acid-sodium dichromate etched beryllium.27... 

Titanium is widely used in aerospace applications that require high strength-to-weight ratios at elevated temperatures. As a result, a number of different prebonding surface preparation processes have been developed for titanium. These generally follow the same sequence as for steel and other major industrial metal substrates degrease, acid-etch or alkaline-clean, rinse and dry, chemical surface treatment, rinse and dry, and finally prime or bond. Mechanical abrasion is generally not recommended for titanium surfaces. 

The common surface preparation treatment for epoxy resins is to wipe with solvent, mechanical abrasion, and final solvent cleaning. Epoxy parts can be most easily bonded with an epoxy adhesive similar to the material being bonded. Urethanes, cyanoacrylates, and thermosetting acrylics have also been used when certain properties or processing parameters are required. 

The specific surface preparation can be checked for effectiveness by the water-break free test. After the final treating step, the substrate surface is checked for a continuous film of water that should form when deionized water droplets are placed on the surface. A surface that is uniformly wet by distilled water will likely also be wet by the adhesive since the specific surface energy of water is 72 dyn/cm and of most organic adhesives is 30 to 50 dyn/cm. However, this test tells little about weak boundary layers or other contaminants that may be present on the substrate s surface but still be capable of wetting with water. 

On exposure to water, an anhydrous oxide can become hydrated by physical adsorption of water molecules without dissociation, dissociative chemisorption of water leading to new hydroxy groups, and finally to the formation of superficial oxyhydroxide or hydroxide, such as for MgO [14]. When silica groups are exposed to water for an extended time, their hydroxylation produces polymeric chains of -Si(0H)2-0-Si(0H)2 0H groups which can link up to form three-dimensional silica gel networks. Around 2 nm thick silica gel layers have been observed on silica surfaces prepared by evaporation of silica on mica which were exposed to humid air [70], Thus, it may be postulated that surface groups are present not only in a two-dimensional oxide-liquid interface, but also in a bulk phase of finite thickness extending from the surface into the interior of the solid [71]. 

The same experimental group continued the research (61) by adsorption of carbon nanotubes onto both PS and PMMA particles in the same method, with four different surfactants. Finally, the prepared PS microspheres with adsorbed nanotubes were sonicated in deionised water to test the durability of their association. It was found that individual tubes remain strongly adhered to the PS microspheres surfaces even after exposition to ultrasound. 

The phenomena so far described apply only to the effects produced by any one particular operation. It is often necessary in practice to use a sequence of different operations the deforma tion in the final surface will then be that characteristic of the final operation only if the pre-existing deformed layer is removed completely at each stage of the sequence. This can be achieved in metallographic practice if suitable precautions are taken (7, 36, 37), bat often would not be achieved in an industrial sequence. The final surface would then contain the residuals of one or more of the deformed layers produced by the earlier stages of preparation, and these could be much more extensive than the deformed layer produced bv the final stage itself. 

Considering the catalysts annealed at 710°C it can be observed that the system originating from the carbonates has a lower activity that the sample calcined at 550°C, whereas on the Cu-LaZr [ex oxalate] system the methanol yield is increased if the annealing temperature goes from 550 to 710°C. All these results can more or less be explained by the change of the copper surface area with the preparation and the annealing temperature as described in table 2. Finally each preparation technique needs the use of the best selected annealing temperature labelled in table 2. 

In a second attempt, the NiAl(l 11) surface was re-examined by NICISS and STM where a different surface preparation has been used by annealing the sample finally at 1300 K (instead of 1000 K utilized before [41-43]) in order to dispose of the oxygen contamination [44]. The 180° backscattering patterns for the Ni and A1 signals of the corresponding clean surface are shown in Fig. 2. The intensity of scattered He particles is plotted as function of the grazing angle of incidence v /j (called v /-scan). An easy way to extract from such v)/-scans... 

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