Protection using multilayered coatings

Figure 4.26 Schematic cross-section (left) of a multilayer coating used in the longterm protection of a mosaic. The mosaic was originally gilded therefore, a tiny gold foil is inserted into each tessera. Professor E. Bescher (right) brushing the mosaic with the sol-gel paint. (Photo courtesy of UCLA Daily Bruin). (Reproduced from ref. 23, with permission.)...

Using multilayer ceramic technology, the thickness of the fuel cell is reduced, in part by the use of ceramics fluidic channels and inherent insu-lative characteristics (Figure 6-2). The fuel channels are incorporated inside the ceramic substrates. This allows the fuel to be protected from contaminates as well as allow for sealing due to ceramics ability to be hermetic when designs require complete sealing. This quality provides a mechanical structure which can effectively supply fuel to the MEA as well as seal off the MEA to optimize efficiency and prevent contamination. In addition, the ceramic separator plates are coated with metals which allow for the interconnection between the cathode and anode sides of the MEA for purposes... 

The use of coatings in conjunction with CP is the most popular form of corrosion protection of pipelines. Some of the coatings used are fusion-bonded epoxy, extruded polyethylene, coal tar enamel, liquid epoxy, tape, polyurethane, mastic, and wax. Pipelines with each of these coatings remain in service at the present. The most widely used coating on pipelines is fusion-bonded epoxy. New multilayered coatings are now on the market. 

Multilayer coatings are used in the atomic energy industry for protection against radioactive substances such coatings are applied to readily accessible surfaces of simple configurations, such as walls, floors, and partitions. When the coating has been subjected to radioactive contamination, the outer layer is easily removed or washed off. Certain special plastic formulations are used in the atomic industry as barrier coatings [230]. 

Copper coatings are used both for decorative and for corrosion protection from the atmosphere. Copper coated steels are used as roofs, flashings, leaders, gutters, and architectural trim. Copper undercoats also improve the corrosion resistance of multilayered coatings, specifically in the plating of nickel and chromium. 

Color changes may occur when these pigments are used to color plastics, because of reduction of the vanadate ion in the polymer melt. Thermostable types suitable for coloring plastics are therefore protected by a dense, glass-like, multilayer coating composed of the oxides of aluminum, boron, silicon and zinc. 

In corrosion prevention, therefore, one first has to define the functionality that is required. For example, researchers have shown that corrosion properties of Zn-Ni multilayer coatings are improved when the layers are at a particular thickness - i.e. 2 pm (Fei and Wilcox, 2006). It has been shown that hard coatings used in high-speed tools requiring protection from wear can be improved by producing layers of TiN interspersed with interfaces, which provide additional hardness. Researchers showed that this occnrs when interfaces are spaced at 8 nm (Bull and Jones, 1994). When the layers are thinner than this, the material reverts to its bulk behaviour. 

Corrosion is an electrochemical process leading to a decrease in thickness and strength of materials. Steel is the most widely used metal in industry and has weak resistance to corrosion. Corrosion resistance can be increased with addition of chrome and nickel. Adding of metals causes an increase in the production cost of steel. To develop the corrosion resistance, polyelectrolyte multilayers can be used to coat stainless steel with low cost [14]. The main aim to coat a metal is to protect it from corrosion. The layer-by-layer self-assembly method is used to prepare polyelectrolyte multilayers. Corrosion of metals can be reduced with inhibitors. Severe corrosion protective coatings are used in many apphcation areas such as automotive, steel, pipe, petroleum and hning industry. Polyelectrolyte multilayers (PEMs) are an alternative method to protect the materials from corrosion. PEMs can be produced with anionic and cationic polyelectrolytes. In addition, PEMs has wide application areas such as membrane separation, microfluidies, biocatalytic and analytical separations. Cationic polyaUylamine hydrochloride (PAH), anionic polystyrene sulfonate (PSS), polystyrene suUbnate-co-maleic acid (PSS-co-MA) and polyacrylic acid (PAA) were used to investigate the corrosion protection efficiency of polyelectrolyte. Corrosion rate, corrosion potential and linear polarization resistance were examined as corrosion process parameters. In addition, polydiaUyldimethylammonium chloride (PDADMAC) was used with sulfonated polyetherether ketone (SPEEK) for steel corrosion applications [14]. 

Other relatively inexpensive personal protective items that are not absolutely essential but should be considered are protective garments and gloves. One-piece coveralls with head covers and booties made from lightweight plastic such as Tyvek are relatively inexpensive, semi-repellent, and disposable. These types of suits are used in the nuclear and chemical industries to provide an added protection against contamination. Tyvek suits have sewn seams and are not recommended for chemical protection, except for vapors of low toxic solvents. Saranex-coated Tyvek or other heavy multilayer suits are required for long-term protection from chemicals. These heavier specialized suits significantly increase heat stress and should not be used by untrained personnel. 

Because of the high functional values that polyimides can provide, a small-scale custom synthesis by users or toll producers is often economically viable despite high cost, especially for aerospace and microelectronic applications. For the majority of industrial applications, the yellow color generally associated with polyimides is quite acceptable. However, transparency or low absorbance is an essential requirement in some applications such as multilayer thermal insulation blankets for satellites and protective coatings for solar cells and other space components (93). For interlayer dielectric applications in semiconductor devices, polyimides having low and controlled thermal expansion coefficients are required to match those of substrate materials such as metals, ceramics, and semiconductors used in those devices (94). 

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