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Epoxies are resins that contain the reactive CH(O)CH2 function (called an epoxide or oxirane ring), where the oxygen atom is found in a three-membered cyclic ring arrangement so that it is positioned outside the carbon backbone.
Simple epoxies are synthesized through reaction of epichlorohydrin with the compound, bisphenol-A. The product is usually called the diglycidyl ether of bisphenol-A (DGEBA) or bisphenol-A diglycidyl ether (BADGE). The small-ring geometry of the epoxide functional group at the end of the monomer chain structures makes it ideally suited to chemical addition reactions that lead to full-chain saturation in resin chemistry, which is better known as polymer curing. Cured polymers produce materials of outstanding durability, making them suitable for very demanding applications. Amines are the usual choice for the curing reaction with epoxies, and form the component often referred to as the hardener. Other hardener compounds may include amides or acid anhydrides.
Epoxy chemistry built in this way from structurally more complex analogues creates a host of major industrial applications such as coatings – particularly protective and powder coatings, floor coatings, adhesives, fiber-reinforced polymers and encapsulation materials for the electrical industry. All of these applications demand exceptional durability. Epoxies occupy more than one segment of the coatings sector and may be manufactured into liquid coatings or powder coatings. Anti-corrosion applications of epoxies are found in both forms.
Novolac epoxy coatings are used in areas where there the risk of corrosion or chemical attack is very high, including tank linings where solvents and corrosive or aggressive chemicals may be stored.
In heavy industry, epoxy coatings are used for the protection of steel and concrete where they are subject to mild chemical attack. This includes the dilute presence of corrosive compounds in water, the presence of organic acids – which are much weaker than mineral acids – or acid mists.
Marine applications of epoxy coatings are largely the underwater surfaces of ships and boats where they protect against the corrosive effects of salt water. The main areas are hulls, cargo and ballast tanks and decks where the threat of corrosion is repetitive. In the sea-going environment, salt carried by the wind poses an additional corrosive threat to ships.
Fusion-bonded epoxies (FBEs) are applied mainly to steel pipes, piping connections, valves, fittings, welded areas and so on.
Epoxy powder coatings are used in corrosive environments and especially in propellers, boat trailers and other marine components. Coal tar epoxies are used for sewers, marine docks, ship hulls, pipelines interiors and exteriors, marine barge exteriors, and for metal protection in most chemical and saltwater environments