Adhesion of the layer

Good adhesion of the layer is necessary, but not sufficient, to inhibit corrosion. Indeed, all three films show good adhesion to the surface (the films were scratched to visualize the removal effect, and to increase the... 

The process has been improved over a period so that now very small particles of palladium may be deposited very evenly, and this has been demonstrated to give improved adhesion of the layers of coating to the substrate. 

Insufficient adhesion of the layers already existing on the adherends (lacquers, corrosion protection layers, metal layers)... 

At 1000°C y- and 8-Al203 are rapidly converted into 0-Al2O3, leading eventually to formation of an a-layer. The 0 —> a-transformation is accompanied by a change in transport properties of the layer [5], A 0-layer grows mainly by outward cation diffusion. In this way voids can be produced at the oxide-substrate interface, resulting in a deterioration of the adherence of the layer on the substrate. By contrast, the growth of an a-layer is determined by anion-diffusion, so that the previously formed voids arc filled with oxide. This improves the adhesion of the layer to the substrate. Therefore, the formation of an a-layer is preferred. 

By a comparison of the forces of adhesion of particles Fad as calculated from Eq. (1.42) with experimental data on the detachment of a monolayer, it is easy to establish that ad corresponds to the force of the most weakly held particles of the monolayer, i.e., the initial section of the integral curves for adhesive force (see Fig. 1.2). Consequently, in the detachment of a powder layer by tilting a dust-covered surface, we measure the average force of adhesion of the readily removable particles. As they sUde, these particles produce an avalanchelike removal of the remaining particles. If the force of adhesion of the layer to the substrate is greater than the autohesion in the layer, the detachment will take place across the weakest autohesive bonds. 

The sign of the charge cannot affect the adhesion due to image forces (see Section 16). In the case of symmetrical charging, when a layer of adherent particles is formed, there may be a discharge and a decrease in the forces of particle autohesion in the layer and the force of adhesion of the layer to the surface, by an amount equivalent to the Coulomb component. 

Denudation of Erosion. In the detachment of an adherent layer of dust by an air stream, the following processes may take place removal of upper particles, i.e., overcoming the forces of autohesion detachment of the dust layer, i.e., overcoming the forces of adhesion of the layer and detachment of the individual particles remaining after removal of the layer. The removal of the upper layers is possible when Fad >Faut- In this case, the dust is raised only a relatively short distance above the original surface. The autohesion process of dust-layer removal is termed erosion [279]. 

A mixture of glass fibres, 12-55 mm long, fillers, and catalysed polyester resin sandwiched between 2 polythene sheets to prevent adhesion of the layers and facilitate handling. Two processes are used to make SMC s giving laminates with slightly differing properties ... 

Neither the native, fibrous nor the microcrystalline cellulose requires additives tor improviiig adhesion. The adhesion of the layers is many times greater than that of inorganic adsorbents dried layers can be wiped. Addition of gypsum to cellulose powders may infiuence separations favourably or unfavourably. Thus it has interfered in amino acid separations [25, 769] and has improved the thin-layer chromatographic separation of nucleic acid products [130]. 

Poured and cut mirror glass is plane but difficult to obtain in sheets of precisely identical thickness. Borosilicate glass is used so that reactions may be carried out on the plate at temperatures of up to 250° C. Frosted glass has been suggested to improve adhesion of the layers [340]. Firmly adhering, dry adsorbent layers can be prepared on sand-blasted glass (verre sable), ready for chromatography [766]. 

There are some well-known methods of raising the efficiency of electric filters by increasing the autohesive forces between the particles. Ferromagnetic iron oxide particles merge and become larger under the influence of an electric field they then stick to the electrode surface in the shape of acicular formations [374]. The enlargement of the particles promotes a rise in the specific resistance and hence in the adhesion of the layer. 

Some alternative chromate free pretreatment methods for aluminium surfaces have already been described [14 16], Commercially available products mainly consist of titanium and zirconium compounds. Hybrid polymer sol-gel materials are potential substitutes for hexavalent chromium-based surface treatments as well. Due to the chemical characteristics, in particular, the presence of hydroxy and alkoxy groups, the hybrid materials are qualified to coat metal as well as metal oxide surfaces. These groups can react with OH-groups on the surfaces of both metals and metal oxides. Water and alcohols are eliminated, while bonds between the hybrid polymer and the metal surface are created (Fig. 6.6), thus leading to good durable adhesion of the layers to the metal substrates [17,18]. Similar to silane adhesion promoters, the hybrid sol-gel materials can also link to organic polymer paint systems (Fig. 6.7). 

The process does have limitations. There is a need for the skin and core materials to be compatible with each other in terms of adhesion and shrinkage. Adhesion of the layers is necessary to prevent the core material becoming detached from the skin especially if the moulding is likely to be exposed to mechanical loads. Therefore materials must be compatible or a suitable compatibiliser used in the core component. The use of compatibilisers in the core component of co-injection moulding was developed and patented by the Rover Group in collaboration with University of Warwick [1]. Researchers from Warwick have also developed and reported methods to mechanically interlock immiscible materials for co-injection moulding but these are currently in the early development stages [2]. 

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