Sealers, corrosion protection

Epoxy based primer systems remain the best suited for the corrosion protection of magnesium. Cathodic epoxy electrophoretic paints , chromate inhibited epoxy-polyamide primers and high temperature stoving epoxy sealers are used to provide protection up to 180°C. For higher temperature applications up to 300°C, epoxy silicone or polyimide based systems can be used. 

Corrosion can be controlled by Isolation of the metal from the corrosive environment by suppression of the anodic dissolution of metal and by suppression of the corresponding cathodic reaction. Isolation of corrosion prone metals from corrosive environments is probably the most general mechanism of the corrosion protection afforded by paint films, sealers, and similar polymer-based materials. Effective isolation requires that polymeric materials have good barrier properties and remain adherent in the presence of water and the products of metallic corrosion. Barrier properties and adhesion aspects of corrosion control are discussed in detail in subsequent sections. 

Adhesives and sealers can be an important part of a total corrosion protection system. Structural bonding procedures and adhesives for aluminum, polymer composites, and titanium are well established in the aerospace industry. Structural bonding of steel is gaining increasing prominence in the appliance and automotive industries. The durability of adhesive bonds has been discussed by a number of authors (see, e.g., 85). The effects of aggressive environments on adhesive bonds are of particular concern. Minford ( ) has presented a comparative evaluation of aluminum joints in salt water exposure Smith ( ) has discussed steel-epoxy bond endurance under hydrothermal stress Drain et al. (8 ) and Dodiuk et al. (8 ) have presented results on the effects of water on performance of various adhesive/substrate combinations. In this volume, the durability of adhesive bonds in the presence of water and in corrosive environments is discussed by Matienzo et al., Gosselin, and Holubka et al. The effects of aggressive environments on adhesively bonded steel structures have a number of features in common with their effects on coated steel, but the mechanical requirements placed on adhesive bonds add an additional level of complication. 

Performance of Stainless Steel Rebar in Concrete Corrosion protection of steel rebar can be achieved by (i) selection of corrosion-resistant steel (ii) use of coatings (iii) addition of corrosion inhibitors such as calcium nitrite to concrete mix (iv) addition of concrete sealers (iv) use of membranes (v) use of thicker concrete overlay (vi) cathodic protection. 

Uses Binder, film-former in paints (printed circuit board coatings, coil, container, conosion-protection, marine, metal, plastics, sealers, tarp, wood varnishes), printing inks (screen printing), primers (adhesion pro-motion/corrosion protection), ceramic compds., sealers, heat-sealable lacquers, two-pack paints, resinous/polymeric food-contact coatings reactive resin in two-pack systems, e.g., crosslinked with melamine/phenolic resins... 

The sprayed coating contains voids (typically 10-20% by volume) between coalesced particles. These voids have little effect on the corrosion protection since they soon fill up with zinc corrosion products and are thereafter impermeable. However, the use of a sealer to fill the voids improves appearance in service and adds to life expectancy, but more important it provides a better surface for subsequent application of paints. 

Sealers play an important role in automobile corrosion protection by preventing water and contaminants from entering crevices and joints. They are usually rubber, vinyl, asphaltic, or hot melt or wax compounds [24,25]. The choice depends on the specific application such as at door hem flanges, brackets, fasteners, and body joints. Structural adhesives are also used to bond assemblies such as doors, deckUds, and hoods, thereby sealing crevices and eliminating welds. 

Concretes made with Portland cement have a specific weight of 140 to 150 Ib/ft (2,242 to 2,400 kg/m ). Concrete absorbs the heat of a fire when chemically bound water is released from a crystalline structure and is reduced to lime. Dense concretes can be formed in place, or pneumatically sprayed to the required thickness using steel reinforcement. The corrosive effect of chlorides on the steel surface in moist saline environments (coastal or other chloride environments) dictates the use of protective primers and topcoat sealers. Major advantages of dense concrete are ... 

A sacrificial or consumed anode can be used instead of coated titanium. Copper was tried in the early 1970s trials but copper (or its salt,s) may accelerate corrosion if it gets into concrete. Steel mesh has been used more recently but has fallen out of favour as it may be completely consumed in some areas before the treatment process is over. It also causes rust staining, although this is not a serious problem as the structure is usually cleaned by water or abrasive blasting after treatment for the application of a protective coating or sealer to prevent further chloride ingre,ss,... 

For better protection against corrosion in spot-welded seams, the seams are treated additionally with an elastic adhesive/sealant (spot-weld sealer) based on rubber. Hot-and cold-application systems are in use. 

Exhaust stacks for gas turbines should be fabricated in corrosion-resistant carbon steel. Also, stacks should be protected externally by an aluminum metal spray with an aluminum silicone sealer. Care should be taken to ensure that the design eliminates thermal fatigue. 

It is necessary to protect anodic coatings (particularly the porous ones) with sealers or paints, especially when exposed to acids, marine environments, or other corrosive conditions. 

Where protection is reqnired against atmospheric corrosion only (e.g. nnder rural conditions), it may not be necessary to use sealer, provided an adequate fihn thickness of sacrificial metal contained, for example, in a metalhc or inorganic zinc coating, is applied. Otherwise an apphcation of sealer is a necessity, observing that it is in the interests of the proprietor of a utihty to avoid repetition of expensive overall preparation of surface. Sealer extends the effectiveness of anti-corrosive composition and the anti-corrosive composition prevents the onset of corrosion that penetrates through damaged and porons sealer. Both are complementary to each other. 

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