Surface pretreatments applications

A study of the pretreatment application and the surface prior to deposition indicates that the aluminum alloy panels have a marked sensitivity to the buildup of a fluorocarbon background in the plasma reactor. This study also showed that the application of the O2 plasma treatment modified the alloy surface, changing it... 

For the electronics and biomedical applications, the galvanic displacement deposition can be successful when very thin films are required and when an appropriate surface pretreatment is carried out to achieve a good adhesion of the deposited metallic film. 

Following the surface preparation, it is the task of surface pretreatment to generate the adhesive forces on the adherend surfaces required for the development of a strong bonded joint. Since almost all materials interesting for bonding have the property to cover the surfaces with impurity layers (oxides, rust, dust, greases), those layers have to be completely removed prior to adhesive application, since otherwise failures in the development of the adhesive forces will occur (Figure 7.5). 

The group of chemical surface pretreatment methods also includes pickling. Here, thinned acids are applied, which remove layers on the metal surfaces via chemical reactions resulting in metallically clean surfaces. The respective application regulations apply, too. 

For the application of the explained surface pretreatment methods and their effects, the structure of surface layers typical for metal materials will be described below (Figure 7.7). 

The adsorption and contamination layers shown in Figure 7.7 are removed during the mechanical surface pretreatment. Such layers, for example, adsorbed moisture or dusts, quickly develop again on clean surfaces. For this reason, the time between the surface pretreatment and the application of the adhesive should... 

If possible, carry out the adhesive application immediately after surface pretreatment. 

For the production of bonded joints with metal materials, appropriate surface pretreatment is of priority. In the technical literature, various formulations of pickling solutions are to be found, their application, however, is limited for reasons of occupational safety and due to the disposal problem. Therefore, we refrain from describing them here. 

In contrast to this, mechanical surface pretreatment methods, as described in Section 7.1, are universally applicable. With the process steps... 

In most cases, adhesion fractures are a sign of insufficient surface pretreatment. In the case of mixed fractures, the reason is to be seen, with high probability, in an incomplete or uneven degreasing. The neglected degreasing after blasting can also be seen as a cause, if the compressed air has not been absolutely fat-free. A cohesion fracture may be the consequence of an adhesive layer not completely cured or of the application of an inadequate adhesive mix. 

In this paper, we present test results of two methods for surface pretreatment which are generally applicable under atmospheric conditions and which can be integrated in the production line. Pragmatic approaches for the numerical description of the material behavior of adhesives according to specific loading conditions are given. Furthermore, we present model parameters for some commercial adhesive systems which were tested in relevant conditions. A concept of knock-down factors and characteristic values which is widely used in component design will be discussed. Experimental results were used to manufacture a fuUy bonded structural component of a rail vehicle. Test results are compared with FE-model predictions. 

The c jerational nature of specific surface area precludes any interpretation of its numerical values in an absolute geometric sense. There is no specific surface area of a soil clay, but only specific surface areas, each determined with some surface chemical application in mind. If the extent of sample alteration produced by required pretreatment is large, then the soundest use of the numerical results from a given method is simply a comparison of values for different soil clays prepared under standardized circumstances. If a chemical reaction is the basis for the measurement, then the results are meaningful only if applied to molecules similar to the probe molecule reacting with surfaces similar to those in the measured sample. It is this operational context that underlies the discussion of experimental methods to follow. 

Another potential source of corrosion problems is in the manufacturing process used to produce the aircraft. Specifically, the assembly and finishing processes can determine whether a specific component will be subject to premature corrosion. Of particular importance is the proper surface pretreatment and application of protective coatings and sealants, which must offer long-term durability to provide adequate corrosion protection. 

The successful performance of many every-day products, and many common materials and construction techniques, is dependent upon adequate adhesion between two or more constituents. Most engineers, however, have only the haziest of ideas about the whole concept of adhesion. For to know how to prepare substrate surfaces for bonding does not necessarily require a knowledge of why adhesive materials should stick to them. It is the intention of this chapter to connect theory with practice, to enable the reader to appreciate why before discussing aspects of surface pretreatment pertinent to applications of adhesives in construction. 

In the practice of adhesive bonding for applications in construction, surface pretreatment is likely to be the most difficult process to control. The choice of treatments must be tempered by the scale of operations, the nature of the adherends, the required durability, the adhesive to be used, and the cost. The performance of joints constructed with cold-cure epoxies is likely to be critically dependent upon surface preparation, as exemplified by the experience of the Scottish Irvine Development Corporation. In 1978 they elected to use vertical externally-bonded steel plate reinforcement to strengthen the abutment walls of three pedestrian underpasses. A year later, the plates were reported to be falling off, accompanied by extensive interfacial corrosion the steel surfaces had been abraded by hand, and the concrete surfaces chemically etched. 

The working characteristics of the adhesive relevant to the application conditions must be determined. For instance viscosity is often temperature, shear-rate and time-dependent, and this will influence the choice of dispensing equipment, the method of application, the usable life and the open time. The viscosity should therefore be regulated bearing in mind the adherend rugosity and surface pretreatment, the method and location of application, and the cure temperature and duration of application. A thixotropic material may be required for application to vertical or soffit surfaces. Generally, relatively thick bondlines are encountered so that the adhesive should be able to cure in thick and/or uneven layers. It should also be remembered that for about every 8 C change in... 

The bonding of aluminium alloy components for structural engineering applications has been the subject of extensive research by the Dutch TNO Institute for Building Materials and Structures(19, 20). Apart from the evaluation and testing of a number of adhesive systems, experimental research was carried out on several structural details. Aluminium alloy surface pretreatment was by degreasing only, to represent a practical procedure. 

There are a number of materials used for the fabrication of pTAS devices. Perhaps the most common is glass due to its low cost, ease of machining, and suitability for electrophoresis and electroosmotic flow (EOF) applications without requiring surface modifications. It is also chemically inert to most reagents (apart from hydrofluoric acid and concentrated alkali). Silicon is also a valuable material that has similar chemical inermess and can easily be machined by chemical etching. While it is more expensive, it can be easily chemically etched to yield far higher aspect ratios than are possible with glass. Silicon is not suitable for electrophoresis or EOF applications without surface pretreatment. Devices fabricated from polymers such as polymethylmethacrylate (PMMA) and polydimethylsiloxane (PDMS) are also frequently used due to the low cost of the material (especially important for disposable devices) and the ease of fabrication. Perhaps one drawback with polymers is their incompatibility with solvents. They are suited to electrophoretic applications but frequently require surface modification to support EOF. Occasionally, metals are used however, these are far more frequently encountered in chemical microreactors. 

Organic coatings are widely used to protect metal surfaces from corrosion. The effectiveness of such coatings is dependent not only on the properties of the coatings, which are related to the polymeric network and possible flaws in this network, but also on the character of the metal substrate, the surface pretreatment, and the application procedures. Therefore, when considering the application of a coating, it is necessary to take into account the properties of the entire system. 

Suitable methods of surface pretreatment for mass-production applications must be discussed and coordinated with the technical service department of the adhesive manufacturer. Adhesive manufacturers have established treatment methods for the main substrates encountered in industrial production and working instructions for users. They are in a position to offer their customers the best professional advice. This approach offers the right chemical pretreatment, which contributes best to the specific adhesive system. Table 4 lists the typical surface pretreatment options for a range of common substrates. 

Typical Applications Epoxies, phenolics, meleunines, nylons, PVC, acrylics, polyolefins, polyurethanes, nitrile rubbers and fiberglass-reinforced thermoplastics used to couple inorganic fillers or reinforcing materials with resins surface pretreatment of fillers and reinforcers. 

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