Protective coatings metals

PEG-2 stearate PEG-2 stearate SE coatings, protective hygroscopic powders Glyceryl stearate coatings, protective metals Tall oil hydroxyethyl imidazoline coatings, protective mineral tablets Castor (Ricinus communis) oil coatings, protective pharmaceutical vitamin/mineral preps. 

Intermetallic compounds with gallium are used as semiconductors. Indium is used to coat other metals to protect against corrosion, especially in engine bearings it is also a constituent of low-metal alloys used in safety sprinklers. The toxicity of thallium compounds has limited the use of the metal, but it does find use as a constituent of high-endurance alloys for bearings. 

Lead azide tends to hydrolyze at high humidities or in the presence of materials evolving moisture. The hydrazoic acid formed reacts with copper and its alloys to produce the sensitive cupric azide [14215-30-6] Cu(N2)2- Appropriate protection must be provided by hermetic sealing and the use of noncopper or coated-copper metal. 

Two basic methods are used for the appHcation of protective coatings to metal containers, ie, roUer coating and spraying. RoUer coating is used if physical contact is possible, eg, coating of metal in sheet and coil form. Spraying techniques are used if physical contact is not possible, eg, to coat the inside surface of two-piece drawn and ironed can bodies (see Coating processes). 

When the operating temperature exceeds ca 93°C, the catalytic effects of metals become an important factor in promoting oil oxidation. Inhibitors that reduce this catalytic effect usually react with the surfaces of the metals to form protective coatings (see Metal surface treatments). Typical metal deactivators are the zinc dithiophosphates which also decompose hydroperoxides at temperatures above 93°C. Other metal deactivators include triazole and thiodiazole derivatives. Some copper salts intentionally put into lubricants counteract or reduce the catalytic effect of metals. 

R. Manory and A. GriU, Protective Coatings of Metal Sufaces by Cold Plasma Treatments, NASA Technical Memorandum 87152, National Technical Information Service, Springfield, Va., 1985. 

Eor steel and other ferromagnetic materials, property deterrnination is more difficult. Other tests are made to measure the continuity of protective metallic coatings. Residual stresses induced in welded stmctures and in components in service owing to chemical attack may contribute to early failure. 

An important function of many coatings is to protect metals, especially steel, against corrosion. Corrosion protection is required ia two different situations ia one case, the steel is protected against corrosion with iatact coating films ia the other case, the objective is to protect the steel against corrosion even when the film has been mptured. 

Separate the metal from the environment with a physical barrier. Many corrosion inhibitors make use of this principal to protect metals. Proper use of an appropriate inhibitor may reduce or eliminate pitting. Pits are frequently initiation sites for corrosion-fatigue cracks. The effectiveness of inhibitors depends upon their application to clean metal surfaces. An example of this method is the use of zinc coatings on steel to stifle pit formation. 

Impressed current anodes are also built in and insulated through sockets or holes in the object to be protected as in Fig. 20-6. With coated valve metals, a region of about 200 mm from the connection is uncoated. In the case of an inter-... 

CoiTosion prevention is achieved by correct choice of material of construction, by physical means (e.g. paints or metallic, porcelain, plastic or enamel linings or coatings) or by chemical means (e.g. alloying or coating). Some metals, e.g. aluminium, are rendered passive by the formation of an inert protective film. Alternatively a metal to be protected may be linked electrically to a more easily corroded metal, e.g. magnesium, to serve as a sacrificial anode. 

This appears as a random non-branching white tunnel of corrosion product either on the surface of non-protected metal or beneath thin surface coatings. It is a structurally insensitive form of corrosion which is more often detrimental to appearance than strength, although thin foil may be perforated and attack of thin clad sheet (as used in aircraft construction) may expose the less corrosion resistant aluminium alloy core. Filiform corrosion is not commonly experienced with aluminium, as reflected by the insignificance afforded it in reviews on the phenomena (Section 1.6). 

Although the initial choice of coating material applied for reasons (b) or (c) may be dictated by the particular properties required, the corrosion behaviour of the composite metal coating/metal substrate system must also be taken into consideration in so far as it may affect the maintenance of the desired properties. Consequently, in all cases where protective metal coatings are used the corrosion performance of both coating and substrate require careful consideration. 

The efficacy of polymers when used to protect metals from corrosive environments is influenced by their efficiency as barrier materials. When applied to metals by some techniques, such as fluidised bed coating, there is always the danger of macro-diffusion through pinholes which are gross imperfections in the surface and which do not have to be visible to be very much greater than the dimension of penetrating molecules. 

To determine whether a protective metallic coating will retard or accelerate corrosion of a basis metal, and to what distance either effect will extend, specimens in which strips of various widths are left bare or made bare have been used by Subcommittee 11 of ASTM Committee B-8 . The extent of corrosion in and near the bare strips as compared with that on a... 

Treating petroleum oils with 3-5% calcium alkyl salicylate and 0.5-3% triethanolamine salts of phosphoric acid esters and ethoxylated dodecyl alcohol increases oxidation-thermal stability at 180-200°C in the manufacture of oil for metal parts quenching. The agent provides also short-term anticorrosion protection of the hardened articles [261]. Phosphoric acid salt alkyl esters are used in anticorrosives and aqueous dispersions in waterborne polyester coatings for metals [244]. 

Because of its relatively low melting point (232 °C) and good resistance to oxidation, tin is used to provide protective coatings on metals such as iron that oxidize more readily. Tin cans are iron cans dipped in molten tin to provide a thin surface film of tin. Traditional metalsmiths use a similar process, coating copperware with a thin film of tin. 

In some cases, the oxide-coating protects the surface from further oxide buildup. One example is that of aluminum where an oxide coating appears almost instantaneously once the pristine surface is exposed to air. Yet, there are many cases where the oxide layer continues to buildup until the metal is totally consumed (One example is that of iron and "rust"). How is this possible Wagner hypothesized that both metal and oxide ions difiosed through the metal oxide layer so as to build up the layer thickness from both sides. The following diagram is one representation of such a mechanism ... 

Electrochemical and nonelectrochemical ways to protect metals against corrosion can be distinguished. The nonelectrochemical ways include dense protective films that isolate the metal against effects of the medium and may be paint, polymer, bitumen, enamel, and the like. It is a general shortcoming of these coatings that when they are damaged mechanically, they lose their protective action, and local corrosion activity arises. 

Hot dip coating is the process of coating a metallic workpiece with another metal by immersion in a molten bath to provide a protective him. Galvanizing (hot dip zinc) is the most common hot dip coating. 

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