why does painting a metal surface prevent corrosion??
110331
Corrosion is the result of metal oxidizing. When metal comes in touch with air, the water vapor and oxygen content of the atmosphere react with the metal to cause rusting/corrosion. \n\nIf you were to cover the metal with a non-water based paint, like in automobiles, this process is then reduced, in fact it is stopped for sometime -till the time the paint and its base coats remain intact.
1185511
There are many different methods, but basically it is a form of preventing or slowing a chemical reaction between metals and air or other impurities. Eg. Painting, plastic dip coating, anodising.\n\n“Corrosion: A partial or complete wearing away, dissolving, or softening of any substance by chemical or electrochemical reaction with its environment. The term corrosion specifically applies to the gradual action of natural agents, such as air or salt water, on metals”.\n\nAlso Fretting corosion:\nFretting corrosion refers to corrosion damage at the asperities? of contact surfaces. This damage is caused under load and in the company of repeated relative surface motion, as induced for example by vibration\nOther causes:\n• corrosive environment\n• contact load\n• amplitude and frequency of load fluctuations\n• cycles\n• temperature\n• availability of moisture\n\nPrevention for fretting Corrosion: \n• Use of lubricants and surface coatings designed to improve lubricity and limit metal-on-metal wear. \n• Increased surface hardness. \n• Use of barriers to limit ingress of corrosive environment to mating surfaces. \n• Reduce bearing loads on mating surfaces.
26245
to prevent oxidation and to make the solder flow better.
828683
I have three reasons -\n\n1. Brass is extremely resistant to corrosion due to its two main components. These are Copper and Zinc. Different grades of Brass are created by varying the levels of each component.\n\n2. The relatively low melting point (900–940 °C depending on composition) of brass and its flow characteristics make it a relatively easy material to cast. Hence ideal for fancy Taps!!!\n\n3.Its yellow colour, obviously similar to gold. It is relatively resistant to tarnishing. Although most modern taps will be plated with Chrome, Older Antique Brass Taps can be easily cleaned and polished to look like new.
876346
Corrosion is defined as: the chemical or electrochemical reaction between a material (usually a metal) and its environment that produces a deterioration of the material and its properties.\n\nAny chemical (or electrochemical) that will deteriorate one or more properties of the composite will be sufficient.\n\nTake a simple electrochemical reaction, for example - without a UV coating, fiberglass (which happens to be a composite) loses tensile strength on prolonged exposure to sunlight.
1047332
once metal is painted, then it has to be continually touched up and repainted and becomes a costly maintenance item, and not an easy place to build a scaffold. Whereas leaving the metal bare will last and retain it's look for a very long time.
836179
water and oxygen are 2 things which cause rusting..in this case there is lots of water and lots of oxygen in the boiling water plus there is the catalyst of heat..\n\nbut by painting it with aluminium paint the surface of alumnium reacts to form an unreactive strong layer of AL2O3 this protects alumninium from furtherly rusting and the iron or steel behind the aluminium>>>plus they usually do this instead of using completely aluminium pipes because its more economic to use steel and paint with aluminium instead of making aluminium pipes plus steel is much stronger
348589
As the above answerer states, you don't need to - titanium won't rust; rather it develops a protective, inert oxide layer in air, just like aluminum has it's protective  inert oxide layer - Al2O3.\nIron and steel rust/oxidize in air and it can prevented by giving a coating of zinc, chromium, or magnesium on it.
112405
It is evidently the chrome, etc. covering of plastic parts to make them gleam bright.  It may start with non-electrolytic coating(s) that can then be electroplated.
1068226
I don't know that it does in general.\n\nIt may be that the Al was easier to abrade, and give a greater surface area...say compared w/ a hard stainless steel.\n\nAbrading the surface (then cleaning w/ alcohol)  is standard protocol for applying adhesives to metals and plastics.
254607
A metal's corrosion (rusting) rate depends on its chemical properties. Some metals just take longer than others to corrode. Keep in mind that most metals have very high melting temperature, so in general high temperature doesn't contribute to the corrosion of a piece of metal just sitting in a damp space. For temperature to be of concern, it has to be around 700 degrees Celsius.\n\nI don't know much about your experiment, but you might not be using an appropriate metal sample. Most commonly found metals come with coatings or contain chemical inhibitors to prevent corrosion. Think about bikes sitting in outside in a humid (moisture-rich) environment. Manufacturers have to coat the metals to prevent this corrosion, or else no one would buy their product. This is the case with most metals. So if you just picked up something laying around the house and tried to corrode it, your experiment might not be successful. You should also be aware that only ferrous (iron) alloys rust, and the particular metal you tested might be something else.\n\nGo to google and type "rusting metal" (without the "s). The first four sites have lots of info.\n\n*It wouldn't rust in the freezer because there's no moisture in the freezer.
302323
Although the type of corrosion most of us are familiar with involves molecular oxygen, corrosion, in general, does *NOT* require the presence of free oxygen.  \n\nFor example, galvanic corrosion, which can occur when two dissimilar metals with different oxidation potentials are in electrical contact.  The less noble metal will form an anode, and be oxidized, while the more noble metal will form a cathode, where reduction reactions will occur.  In the absence of oxygen, reduction reactions like:\n\n  2H+ * 2e- -> H2(gas)\n\ncan occur.  This reaction is particularly important in acidic environments, (when the H+ concentration is high).  Such environments can develop in corrosion environments via hydrolysis reactions, e.g., \n\n  Fe3+ + 3H2O -> Fe(OH)3(solid) + 3H+\n\nwhere the Fe3+ ions are produced by the oxidation of iron metal, and Fe(OH)3 is the solid mineral "goethite", a major component of "rust".\n\nCorrosion can also be induced in the absence of free oxygen by the action of some species of bacteria. For example, there are bacteria that can reduce sulfate ions (SO4--) or nitrate ions (NO3-) to hydrogen sulfide (or metal sulfides) and molecular nitrogen.  To do so, they need to couple these reactions to a "source" of electrons, which can be a metal surface that is then oxidized (i.e., corroded). \n\n\nFinally, there are some metals that are themselves strong reductants -- so strong that they can reduce water.  Li, Mg, Na, and Al all have standard oxidation potentials that are lower than that of water, so they will react spontaneously (in the case of Li and Na, *violently*) with pure water (even water containing no free oxygen) to form metal ions or hydroxides and hydrogen gas.
379742
Galvanising iron is nothing but a process of coating iron with a thin layer of zinc by electroplating. The main idea behind this is that zinc is a 'sacrficial metal' as it is highly electropositive.\n\nWhat actually happens when you expose normal 'ungalvanized' iron to the atmosphere is that it reacts with oxygen and moisture to form a mixture of iron oxides(rust).\n\nOn the other hand, when galvanized iron is exposed to the atmosphere, it is in fact not the iron, but the ZINC which is exposed to the atmosphere. Now it is ZINC, which undergoes oxidation(not iron as in the case above). This leads to the formation of  a thin film of zinc oxide over the actual zinc(which was coated over iron). Zinc oxide acts as a protective layer and prevents further amount of zinc(or iron) from being exposed to the atmosphere.\n\nSo that's the whole story behind 'Why galvanized iron lasts longer than ordinary iron'. \n\nAnd 'IBL' or whoever you are, please do not copy essays from encyclopedias. Even if you do, have at least the minimum decency and courtesy to copy 'relevant' information.\n\nIt's an insult to ppl who really know chemistry out here.
125784
Painting seals the surface, protecting it from corrosive elements.
866699
Plating metals can be electrolytic or electroless.  The metal is oxidized from elemental state to charged state. Ie Cu will go to Cu++ in solution and then reduced to Cu on a charged metallized object.  Powder coating uses a powder spray, is then heated to form a layer around the object.
102293
corrosion is caused by the chemical reaction of oxygen with the metal over time, thus causing rust.  In order to help preserve the metal, a layer of paint is used that will serves as a shield or barrier between the oxygen and the metal.
161336
It doesn't always stick where it is suppose to. Sometime you need solder flux to be applied before it will stick. I imagine that the reason it won't stick to painted metal is that it need to be on clean metal for it to stick. I always like cleaning up the little splashed on the floor from solder.