Iron oxide protective coating

Drill Pipe. Iron oxide pigmented coatings are used to protect oil well drill pipe. In this application, phenolics are required for their resistance to abrasion, acids, hydrocarbons, and water at high temperatures and pressures, as encountered in drilling operations. 

Paint is one of the most common and widely used materials in home and building constmction and decoration (see Building materials). Its broad use comes from its abiHty to provide not only improved appearance and decoration but also protection of a substrate to which it is appHed. Evidence of the historical uses of paint goes back over 25,000 years to cave paintings found in Europe. The Bible describes pitch being used to coat and protect Noah s Ark. Over 10,000 years ago in the Middle East, various minerals and metals such as lime, siHca, copper and iron oxides, and chalk were mixed and reacted to produce many colors. Resins from plant sap and casein were also used. Over 2000 years ago in Asia, resins refined from insect secretions and sap from trees were used to make clear lacquers and varnishes (2). 

A frequently cited example of protection from atmospheric corrosion is the Eiffel Tower. The narrow and, for that age, thin sections required a good priming of red lead for protection against corrosion. The top coat was linseed oil with white lead, and later coatings of ochre, iron oxide, and micaceous iron oxide were added. Since its constmction the coating has been renewed several times [29]. Modern atmospheric corrosion protection uses quick-drying nitrocellulose, synthetic resins, and reaction resins (two-component mixes). The chemist Leo Baekeland discovered the synthetic material named after him, Bakelite, in 1907. Three years later the first synthetic resin (phenol formaldehyde) proved itself in a protective paint. A new materials era had dawned. 

The outstanding virtue of zinc-rich paints is simplicity in application. No special equipment is required and the operation can, of course, be carried out on site, large or small structures being equally suitable for treatment. While there is some evidence that the zinc-rich paints will reduce iron oxides remaining on the steel surface, proper surface preparation is as important here as with traditional paints if the best results are to be achieved. The main use of zinc-rich paints is to protect structural steel-work, ships hulls, and vulnerable parts of car bodies, and to repair damage to other zinc coatings. 

Various strategies are employed to prevent corrosion. The use of paint as a protective coating is described in our chapter introduction. A metal surface can also be protected by coating it with a thin film of a second metal. When the second metal is easier to oxidize than the first, the process is galvanization. Objects made of iron, including automobile bodies and steel girders, are dipped in molten zinc to provide sacrificial coatings. If a scratch penetrates the zinc film, the iron is still protected because zinc oxidizes preferentially ... 

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. 

As long as the tin coating remains intact, the iron is protected from oxidation. A scratch of the tin surface to expose the iron metal leads to the oxidation of iron in preference to the tin. 

Zinc is malleable and can be machined, rolled, die-cast, molded into various forms similar to plastic molding, and formed into rods, tubing, wires, and sheets. It is not magnetic, but it does resist corrosion by forming a hard oxide coating that prevents it from reacting any further with air. When used to coat iron, it protects iron by a process called galvanic protec-... 

Today about one-third of all the zinc metal is used for the process known as galvanization. This process provides a protective coating of zinc on other metals. A thin layer of zinc oxidizes in air, thus providing a galvanic corrosion protection to the iron or steel item that it coats. Several processes are used to galvanize other metals. One is the hot dip method wherein the outer surface of the item to be galvanized is pickled and then immersed into a molten zinc bath. A... 

Cathodic inhibitors promote coverage of iron by a protective coating, but this need not be an iron oxide. Immersion of iron in a solution of phosphoric acid containing a suitable catalyst causes precipitation of a mixed Fe"-Fe " phosphate film which serves as a base for a coating of paint. 

Anticorrosive paints containing pigments with either chemical or electrochemical action may induce formation of protective coatings at the metal-paint interlayer (Etz-rodt, 1993). These protective coating may be metal-substituted iron oxides iron phosphate precipitates or even a green rust - Fe Fe" 0HigC03 4H2O (Chemical Week, 1988). 

A reaction of commercial interest that is apphed in many water treatment processes is for protection against corrosion. The reaction involves oxidation of iron to form magnetite that provides a protective coating on the metal surface ... 

Zinc and zinc-coated products corrode rapidly in moisture present in the atmosphere. The corrosion process and its mechanism were studied in different media, nitrate [283], perchlorate [259], chloride ions [284], and in simulated acid rain [285]. This process was also investigated in alkaline solutions with various iron oxides or iron hydroxides [286] and in sulfuric acid with oxygen and Fe(III) ions [287]. In the solution with benzothia-zole (BTAH) [287], the protective layer of BTAH that formed on the electrode surface inhibited the Zn corrosion. 

In this activity, galvanized nails are used as a source of zinc. Galvanization is a process by which metals such as steel are dipped in zinc to protect them from rusting. One type of nail is dipped in a hot bath of molten zinc to form a protective coating. Zinc is more easily corroded than iron, so it oxidizes rather than the steel. 

Hematite is found in large quantities in the vicinity of Malaga in Spain (Spanish red) and near the Persian Gulf (Persian red). The Spanish reds have a brown undertone. Their water-soluble salt content is very low and their Fe203 content often exceeds 90 %. The Persian reds have a pure hue, but their water-soluble salt content is disadvantageous for some applications. Other natural hematite deposits are of only local importance. A special variety occurs in the form of platelets and is extracted in large quantities in Karnten (Austria). This micaceous iron oxide, is mainly used in corrosion protection coatings. 

Pigments with a physical protective action are chemically inert and are termed inactive or passive. An example is micaceous iron oxide [5.54], [5.55]. These lamellar pigments are packed in layers they lengthen the pathways and obstruct the penetration of ions. They improve adhesion between the substrate and the coating, absorb UV radiation, and protect the underlying binder (Fig. 68), [5.56]—[5.60]. 

Exterior surface corrosion or rusting of pipes occurs by the formation of iron oxides. Painting to an appropriate specification will significantly extend the period to the onset of corrosion, but the durability of the paint finish is largely dependent on the quality of the surface preparation as well as the thickness of the coated film. Improperly installed insulation can provide ideal conditions for corrosion and should be weatherproofed or otherwise protected from moisture and spills to avoid contact of the wet material on equipment surfaces. Application of an impervious coating such as bitumen to the exterior of the pipes is beneficial in some circumstances. Hypalon and neoprene rubber-based anticorrosive coatings admixed with chlorinated rubber are finding use in many installations. 

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