How does painting of metal's surface prevent corrosion?
97708
the metal is simply not exposed to the outside oxygen - it is shielded from it by the paint, which itself contains little, if any oxygen
123326
Most corrosion is on the outside so it really doesn't make a difference, hot or cold. What determines corrosion is the \nenvironment outside of the pipe.
797998
Aluminum will oxidize, but the aluminum oxide forms a coating over the remaining aluminum that prevents further corrosion.\n\nBy contrast, iron oxide (better known as rust) will not form such a coating, it will warp and crumble and expose more iron to rust.
762743
Anodizing relies on an electric current flowing in a liquid solution containing solids of the coating required to be deposited on in this case the aluminium.  If there is a plastic coat over the aluminium there can be no deposit made on the item.
497397
Let's say you're really hungry. If I lock a cupcake in a metal box and give you the box can you get to the cupcake without a key?\n\nNope.\n\nMetal oxides work the same way. By coating a metal in a desirable oxide (ie. as in aluminium anodizing) you're sealing the unprotected metal from more harmful forms of oxidization. If oxygen can't react with the surface of the metal because its already reacted with something else to form an oxide. Because of that you just prevented further oxidization BY oxidizing. There's no key, no reaction, to further degrade the metal underneith.\n\nThere are other things besides oxide coatings that can keep good ole' redox at bay. One is called a sacrificial anode and its commonly used on exposed metal on things like oil rigs.
549460
bmck has it right...prep work on any paint job is about 3x the actual paint time and the more the better...all loose paint must go; any place the aluminum is oxidizing ( loose grey powder, the alum. equivalent of rust) must go. Zinc chromate either in spray cans or quarts is the preferred  general purpose primer..\n\nPaints are usually made as a system, ie a finish coat is made to go with a specific primer. GO to marine store..or, if you are on fresh water and doing very limited use) a hardware store, and read the pant cans. Having spent 30 years reading Interlux and Pettit cans, I know there's a lot of information on the label.\n\nIf you are thinking of putting an anti-fouling paint on the boat you CAN NOT NOT NOT use copper based paints. The copper in salt water will eat the aluminum hull in no time....special paints are made for aluminum; once again read the cans.....THIS ALSO APPLIES TO OUTDRIVES AND OUTBOARD MOTORS, FOLKS..if you're in salt or even brackish water don't use copper anti fouling paint on your engine parts.you will quickly regret it
40274
The magnesium metal buried nearby provides protection from corrosion.  “Corrosion” is the technical name for the chemical reaction that takes place when a metal combines with oxygen.  Magnesium acts as an anode and protects the iron or steel tank by corroding in preference to the iron or steel tank.  This means that instead of Iron giving up electrons that attach to the oxygen atoms(which causes corrosion), the Magnesium releases the electrons.  The Magnesium and Oxygen atoms combine to form magnesium oxide while Iron does not take part in the chemical reaction and is thus protected.\n\nThe corrosion of a magnesium anode in preference to steel is an example of galvanic protection.
769099
Iron is stronger and steel of course is stronger still.  Further, iron corrodes only if not cared for.  Copper will form a patina over time even if cared for.
147407
Rusting is a chemical process that, can take place in metals exposed to the atmosphere. Not all metals however rust. Rusting is common with the metal, iron. Certain conditions in the air around a metal have to be present for iron to rust. Iron rust which, generally appears brown, is itself a chemical compound quite different from the iron itself. The rusting of iron can be prevented. In towns and large cities where iron sheets are used for roofing houses, rusting can also take place if the iron sheets are not protected from rusting. \n\nRust is the common name for a very common compound, iron oxide. Iron oxide, the chemical Fe2O3, is common because iron combines very readily with oxygen -- so readily, in fact, that pure iron is only rarely found in nature. Iron (or steel) rusting is an example of corrosion -- an electrochemical process involving an anode (a piece of metal that readily gives up electrons), an electrolyte (a liquid that helps electrons move) and a cathode (a piece of metal that readily accepts electrons). When a piece of metal corrodes, the electrolyte helps provide oxygen to the anode. As oxygen combines with the metal, electrons are liberated. When they flow through the electrolyte to the cathode, the metal of the anode disappears, swept away by the electrical flow or converted into metal cations in a form such as rust.\n\nFor iron to become iron oxide, three things are required: iron, water and oxygen. Here's what happens when the three get together:\n\nWhen a drop of water hits an iron object, two things begin to happen almost immediately. First, the water, a good electrolyte, combines with carbon dioxide in the air to form a weak carbonic acid, an even better electrolyte. As the acid is formed and the iron dissolved, some of the water will begin to break down into its component pieces -- hydrogen and oxygen. The free oxygen and dissolved iron bond into iron oxide, in the process freeing electrons. The electrons liberated from the anode portion of the iron flow to the cathode, which may be a piece of a metal less electrically reactive than iron, or another point on the piece of iron itself.\n\nThe chemical compounds found in liquids like acid rain, seawater and the salt-loaded spray from snow-belt roads make them better electrolytes than pure water, allowing their presence to speed the process of rusting on iron and other forms of corrosion on other metals.
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Galvanic corrosion tends to occur when dissimilar conducting materials are connected electrically and exposed to an electrolyte. The following fundamental requirements therefore have to be met for galvanic corrosion:\n\n   1. Dissimilar metals (or other conductors, such a graphite).\n   2. Electrical contact between the dissimilar conducting materials\n      (can be direct contact or a secondary connection such as a common grounding path).\n   3. Electrolyte (the corrosive medium) in contact with the dissimilar conducting materials.\n\nWhen placed in an electrolyte, different metals/alloys assume different corrosion potentials (refer to the galvanic series in seawater). It is this potential difference that is the driving force for galvanic current flow. The less noble material in the galvanic couple will become the anode and tend to undergo accelerated corrosion, while the more noble material (acting as a cathode) will tend to experience reduced corrosion effects. However, in some cases, chemical species produced at the cathode can degrade certain cathode materials.\n\nIt is not only the potential difference that controls the magnitude of galvanic current flow. The total resistance to current flow (see schematic of a simple corrosion cell, with both arrows showing conventional current direction) also needs to be considered, which can be broken down further into the following individual resistance components:\n\n   1. Resistance to (ionic) current flow of the electrolyte.\n   2. Resistance to current flow (by electron conduction) in the conducting materials and in the connection between them.\n   3. Resistance associated with polarization behavior of the anode.\n   4. Resistance associated with polarization behavior of the cathode (cathode efficiency).
186001
u forgot to put the foloowings to choose from...\nbut still here are some ideas for u...\nTO PREVENT RUST, KEEP METAL SURFACE DRY - OR ADD A COATING \nRust is corrosion that affects ferrous metals such as iron and steel. In many cases, water vapor must be in the air before rust can occur. With iron, for example, 40 percent humidity must be present before rust will start to occur. The best way to prevent corrosion is to keep metal surfaces dry. Isolating the metal by coating it with paint, lacquer or wax is another good way to prevent corrosion. \n\nBefore coating a metal surface, remove all traces of rust. Then apply a primer and finish with paint. It's best if the paint and primer are the same brand; they usually are formulated to work together. Metals such as brass, copper or aluminum are best protected with either wax or by spraying them with lacquer or clear varnish. \n\nRust also can attack metal in inaccessible areas. Corrosion occurs inside a home hot-water heater, for example, because the ions circulating in the water make it easy for dissolved oxygen to pull the electrons from the interior surface of the metal tank. \n\nRust that occurs in localized areas is called localized corrosion. There are three types: galvanic, crevice and pitting. \n\n- Galvanic corrosion: It occurs whenever two dissimilar metals contact each other. This creates a flow of electrons between the metals that eventually causes them to disintegrate. One way to prevent this corrosion is to replace one metal piece with another that is compatible with the mating piece.\n\nFor example, many aluminum storm doors have steel rivets holding the hinges or closing piston in place. Often, corrosion starts around these fasteners, then works to the adjacent aluminum panels. Drilling the corroded fasteners out and replacing them with aluminum pop-rivets will stop the galvanic corrosion before it spreads.\n\n- Crevice corrosion: It occurs around the joints and seams of metal fixtures where dirt accumulates. By itself the dirt is not particularly harmful, but it allows moisture to collect; this causes corrosion. Joint and seam corrosion is a common occurrence on gutters and downspouts. Clean them often to keep dirt and leaves, which retain moisture, from building up. If rust is present, remove it with a flexible sanding wheel chucked in an electric drill, then prime and paint the bare metal.\n\n- Pitting corrosion: It occurs outdoors when the wind bombards metal surfaces with minute particles of dirt, salt or sand and creates microscopic craters that retain moisture. At first, the corrosion is limited, then quickly escalates into a formidable problem. Outdoor electrical conduits, television antenna masts, metal windows and doors, and children's play equipment are a few of the items that receive constant assault from air-borne particles and are subject to pit corrosion. This type of corrosion is severe near the seashore and is most noticeable on the side of the house that faces the prevailing winds. Check exposed metal surfaces often; sand and paint them if they show signs of pitting.
1027806
When shipping anything metal that has the potential to experience a salt water environment, coat the object in a substance called Cosmoline, which is a waxlike substance that prevents oxidation and corrosion.  It can be found at any Hardware store or Gun shop.
535149
Actually the copper doesn't come directly from the solution...\n\nNot sure how much detail you want, but it does use electroplating.  This means that it uses electricity to plate metal on an object.  The stainless steel object is put on the "positive end" and a lump of pure copper is placed on the "negative end."  A low voltage is used because a high voltage plates too fast, and the layer will peel off quickly.  If copper is the plating, then the solution must be a fairly low-concentration copper sulfate (CuSO4) solution, meaning that copper is the only metal present in the electrochemical cell.  The negative end is called the anode, and this decreases in mass as its copper ions are taken to the positive end -- the cathode.  \n\nThis method of plating multiple metals is actually fairly common, because the properties of each one can be combined.  Nickel can be used for farm equipment and engines because it can withstand a lot of force, silver is used for decoration, chromium is used to withstand a lot of use (like a spoon).  Copper is able to conduct heat and helps food cook evenly.
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Corrosion is the oxidation of a metal.  Oxidized metals do not possess valuable or useful properties.  That is, they are typically more brittle and less conductive.\n\nCorrosion occurs naturally and it is bad when it results in inefficiency or failure of the metal.
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The company I work for does Salt Spray Analysis. it's used to find out how well a coating holds up under controlled conditions. Salt water is very corrosive to most metals and is a good medium for testing for corrosion.\n\nBasically, a part that has a coating (paint, Anodize, Nitride, Black Oxide,...) is placed in a sealed tank. The tank sprays water with a particuar amount of salt in it into the chamber. The parts are checked every hour, 2 hours, 6 hours...as directed by the requirements. As soon as ANY rust is found, the testing stops and the amount of time it took for the rust to show is recorded. 300 hours is very good for any type of paint.
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In soldering of metals, flux serves a threefold purpose: \n\nremoves oxidation from the surfaces to be soldered \n\nseals out air thus preventing further oxidation\n\nfacilitating amalgamation improves wetting characteristics of the liquid solder.
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Passivation accomplishes two things.  First, it removes any stray particles of mild steel that may be present on the surface of the stainless steel.  Second, it builds a protective layer of corrosion on the surface of the stainless steel by slightly corroding the stainless steel itself.  \n\nThis process is desirable when the steel will be subjected to harsh environments, such as submersion or heavy exposure to seawater.