Navair 01-1A-509-1, Cleaning And Corrosion Control Volume I Corrosion Program And Corrosion Theory;

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the electrochemical deterioration of a material or its properties due to its chemical reaction with the surrounding environment.

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Corrosion

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The smallest unit of an element made up of a positively charged nucleus surrounded by a system of negatively charged electrons

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Atom

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a negatively charged subatomic particle

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Electron

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an atom or group of atoms or molecules which has acquired a net electric charge by gaining (negative ion) or losing (positive ion) electrons

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Ion

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a liquid (usually water) solution containing ions.

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Electrolyte

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all metals will corrode to some extent in a natural environment.

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Theory of corrosion

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Four conditions must exist before metal corosion can occur

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a metal which can corrode, dissimilar conductive material, conductive liquid, and electrical contact.

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Most common type of corrosion ( results from a direct chemical attack on a metal surface that proceeds uniformly over the entire exposed surface.

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Uniform surface corrosion

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occurs when different metals are in contact with each other and an electrolyte, such as sea water. (high build up of corrosion deposits at he joint between the metals)

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Galvanic Corrosion

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a form of extremely localized attack that results in holes in the metal. ( first noticeable as white or gray powdery deposits, similar to dust, white blotches the surface when cleaned away tiny pits or holes can be seen in the surface.)

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Pitting Corrosion

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Coating/ sealing the exposed surface will stop this type of corrosion

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Uniform Surface

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potential for galvanic corrosion is greatest when?

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two metal are well separated from each other in the galvanic series and are in electrical contact

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pitting failures are commonly caused by?

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electrolytes containing chloride or chlorine containing ions (such as sea water)

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Most susceptible to pitting damage?

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Stainless steels although aluminum, magnesium and copper are often attacked

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an attack on the grain boundaries of the metal.

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Intergranular Corrosion

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high strength aluminum alloys, which depend on precipitated phases of alloying elements for strength are particularly susceptible to what type of corrosion

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Intergranular

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an advance form of intergranular corrosion where the surface grains of a metal are lifted up by the force of expanding corrosion products occurring at the grain boundaries.

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Exfoliation Corrosion

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this type of corrosion most often occurs on extruded sections of metal and is found primarily on aluminum sheet around steel fasteners.

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Exfoliation

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Exfoliation corrosion prevention involves

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separating the aluminum and steel by a barrier such as zinc-chromate primer or sealant

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one of the most familiar types of corrosion, may occur in any crevice where a stagnant solution has pooled

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Crevice corrosion

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methods to minimize this type of corrosion include closing crevices by welding, sealant, or soldering and use of a nonabsorbent gasket such as teflon.

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Crevice

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a form of crevice corrosion which occurs on metal surfaces having a thin organic protective coating

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Filiform corrosion

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storing equipment and aircraft in an environment with a relative humidity below 65%, by using coating systems having a low rate of diffusion for oxygen and water vapors, by maintaining coatings in good condition and applying corrosion preventive compounds when the coating is damaged.

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Preventing Filiform Corrosion

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the increase in the rate of attack on a metal due to the action of a corrosive fluid against the metal surface.

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Erosion Corrosion

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the intergranular or transgranular cracking of a metal caused by the combined effects of constant tensile stress and corrosion.

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Stress corrosion

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Stress corrosion can be prevented by?

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placing an insulating barrier between the metal and the corrosive environment or by applying protective coatings and/or water displacing corrosion preventive compounds.

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occurs at contact areas between materials under load subject to repeated vibration.

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Fretting Corrosion

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reducing the amount of relative motion at the surface, adding a lubricant at the interface to reduce friction and seal out oxygen, increasing the surface hardness of the part, and increasing the overall hardness of one or both contacting metals. prevent which type of corrosion?

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Fretting

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corrosion in the absence of water can occur with what type of corrosion?

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Hot Corrosion

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High temperature ceramic coatings can reduce this type of corrosion but are usually applied only by the manufacturer due to the highly specialized equipment required for application.

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Hot

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Aluminum is subject to what types of corrosion?

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Pitting, intergranular corrosion and stress corrosion cracking

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Magnesium is subject to what types of corrosion?

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pitting