Duplex coatings

The corrosion rate of a bare sprayed coating is comparable to that of solid zinc or aluminium, although the greater surface area exposed may cause apparent corrosion rates to be a few per cent higher. For most uses, however, the sprayed coating is sealed or painted and achieves the much higher corrosion resistance associated with duplex coatings. The extra life depends on the sealer or on the thickness and type of paint used, and on the environment. 

TiOi) result in substantial improvement in strength and toughness of the composites. The BN coating reduces the interface bond strength between the SiC reaction layer ind the mtitrix. A duplex coating of SiC/BN applied to the Nicalon... 

Figure 7.79 SEM images of Ti6AI4V implants in a femoral bone of a dog. (a) Without a coating and (b) with a HAp/titania duplex coating (Heimann, 2007).

Presently, the so-called duplex coating techniques [27] are used for further improvement of adhesion characteristics of coatings. These imply a two-stage action on the substrate, in particular... 

A well-designed duplex coating is an effective and safe barrier interposed between the construction materials and the environment, and it is effective for a time roughly proportional to the weight of the anodic layer. Its use is not limited to the bright chromium finishes, but it can be extremely appropriate if the corrosion products of the base material are undesirable and if, furthermore, the contact between the material of construction and the environment must be avoided. 

Fig. 8.14 Schematic illustration of stud with applied epoxy attached to a duplex coating [99]...

J.G. Kohl, I.L. Singer, Pull-off behavior of epoxy bonded to silicone duplex coatings. Prog. Org. Coat 36, 15-20 (1999)... 

Schlossman, D. Shao, Y MazzeUa, F. Quinn, C. Preparation and cosmetic use of duplex coated color lake and other powders. U.S. Pat. Appl. Publ. US 2005037041, 2005 Chem. Abstr. 2005,142, 225265. 

Outdoor testing of duplex coatings takes too long—new organic prod-... 

Duplex Coatings (two metal layers). A layer of zinc followed by a layer of another metal (usually aluminum) is occasionally advocated to provide a barrier or more slowly corroding surface initially or to give specific properties such as reflectivity. 

In the thermal spraying industry, a processing benefit of applying zinc first and then aluminum is that the quality of blasting pretreatment required for zinc spraying is less critical than for aluminum, especially when gas pistols are used. Such duplex coatings have been used on Royal Navy ships decks, for example, and also in hot areas, such as near coke ovens, where aluminum helps to reflect heat. 

Vapor deposition remains only a possible commercial alternative for coated steel for cars. High deposition rates and the ease of producing duplex coatings (zinc followed by aluminum or vice versa) with improved coating resistance are potential advantages, but engineering for high speed line use remains to be developed. 

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