What is Corrosion: Definition and 99 Discussions

Corrosion is a natural process that converts a refined metal into a more chemically stable form such as oxide, hydroxide, carbonate or sulfide. It is the gradual destruction of materials (usually a metal) by chemical and/or electrochemical reaction with their environment. Corrosion engineering is the field dedicated to controlling and preventing corrosion.
In the most common use of the word, this means electrochemical oxidation of metal in reaction with an oxidant such as oxygen or sulfates. Rusting, the formation of iron oxides, is a well-known example of electrochemical corrosion. This type of damage typically produces oxide(s) or salt(s) of the original metal and results in a distinctive orange colouration. Corrosion can also occur in materials other than metals, such as ceramics or polymers, although in this context, the term "degradation" is more common. Corrosion degrades the useful properties of materials and structures including strength, appearance and permeability to liquids and gases.
Many structural alloys corrode merely from exposure to moisture in air, but the process can be strongly affected by exposure to certain substances. Corrosion can be concentrated locally to form a pit or crack, or it can extend across a wide area more or less uniformly corroding the surface. Because corrosion is a diffusion-controlled process, it occurs on exposed surfaces. As a result, methods to reduce the activity of the exposed surface, such as passivation and chromate conversion, can increase a material's corrosion resistance. However, some corrosion mechanisms are less visible and less predictable.
The chemistry of corrosion is complex; it can be considered an electrochemical phenomenon. During corrosion at a particular spot on the surface of an object made of iron, oxidation takes place and that spot behaves as an anode. The electrons released at this anodic spot move through the metal and go to another spot on the metal and reduce oxygen at that spot in presence of H+ (which is believed to be available from H2CO3 formed due to dissolution of carbon dioxide from air into water in moist air condition of atmosphere. Hydrogen ion in water may also be available due to dissolution of other acidic oxides from the atmosphere). This spot behaves as a cathode.

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  1. R

    Surface oxidation of aluminum alloy and electrical continuity

    I'm using aluminum alloy (6061-T6 sheet at the moment) to construct a chassis for mechanical support of an assembly. This chassis also serves as part of an EMI mitigation system (RF, GHz range), so I need to ensure electrical continuity between the chassis and other components of the system. I...
  2. T

    Wet corrosion of CuNiFer pipe in seawater

    This CuNiFer alloy pipe is used in a seawater cooling system and is electrical insulted with nearby metals; this prevents galvanic corrosion to occur since there is no contact with other metals. I've seen multiple sources that say CuNiFer is very corrosion resistance. The pipe is still...
  3. T

    Sacrificial Anode on isolated copper alloy pipe

    For a seawater cooling system there is a isolated copper alloy pipe where seawater flows through protected with sacrificial Anode. For galvanic corrosion there needs to be two different metals connected in a presence of an electrolyte, since this isn't the case. For what kind of corrosion is...
  4. H

    Help, I have made a huge mistake with copper sulfate!

    This must be the dumbest thing I have ever done. I used copper sulfate (CuSO4) for an experiment. I first bought copper sulfate in crystalline form and then mixed it in water. After the experiment was done I flashed the copper sulfate down the toilet but some of it was actually absorbed by the...
  5. F

    Stainless Steel corrosion issue

    Not my issue directly, more a case of relaying the problem, but here goes. My girlfriend works for a company that makes bioanalytical units, and is part of their validation team in particular. They’ve started running into an issue with a stainless steel solenoid valve where it is, for lack of a...
  6. wnvl2

    Chemistry Using Pourbaix diagrams to calculate corrosion in water

    Let us solve it for Cu at pH =8. I found this Pourbaix diagram. What is the electrochemical potential I should use to check that Cu is there the stabel form. Should I check for all values of E between the blue lines at pH = 8? How can I measure the E value in reality?
  7. hjannett

    Corrosion resistance of 6105-T5 anodized aluminum for wastewater?

    Hello, I'm looking for structural materials that will act as the frame (skeleton) for the housing surrounding a waste container. The frame will structurally support HDPE panels as walls. This will be above ground for use in Uganda (but we can ship materials), under a raised squat toilet hole...
  8. C

    Aluminum and copper -- Galvanic corrosion

    If a copper water pipe is connected to a piece of aluminum through a copper wire, where will the galvanic corrosion take place? On the wire to aluminum joint eating away at the aluminum, or will the whole water pipe suffer? (does copper corrode aluminum, or vice versa, or each other?) thanks
  9. jra12222

    What are the factors that contribute to crevice corrosion in stainless steel?

    Hi all, I am trying to understand how the process of either crevice or pitting corrosion works (I believe they are quite the same) I understood the part of how they start and what enhances them or how they can be prevented, but I can't understand an actual scenario. Say for example we have...
  10. Joe591

    Possible Causes for Hole in Radiator Tank

    What would cause a hole to form in the top aluminium tank of a radiator of an earthmoving machine. The tank material is 6mm thick and is made from 1050 aluminium plate. The material around the hole has bubbles almost like pitting corrosion or like somebody went and took a flame to it. The rest...
  11. jack action

    Different metal types and corrosion

    I need to bounce some ideas off you for my project. My project is to build an exterior handrail, using these flanges: The actual inner diameter (ID) is 1.66" and the material is galvanized steel. I was supposed to use the appropriate pipe size for the handrail made also of galvanized...
  12. Absentee

    Why does saltwater increase rate of corrosion?

    Why does salt water increase rate of corrosion, really? Most common answer I read was that salt makes water a better electrolyte. No further explanation. However, I'm not really getting the mechanism of this. I understand the mechanism of pitting corrosion in presence of chloride ions and I...
  13. H

    Oxidation of iron and galvanised iron in bleach

    In a laboratory experiment I have tested plain carbon steel in a beaker of bleach (sodium hypochlorite), immersed for a week. The result is a magenta-coloured solution with a large amount of ferrous hydroxide deposits. Q1) I haven't been able to find anywhere anything that might be causing...
  14. B

    Which metals undergo differential aeration corrosion?

    Hi, I am trying to learn about different types of corrosion. I have read that iron can undergo differential aeration corrosion, but not zinc and aluminium. I do not see why...both can be reduced by oxygen and both have a passive film. Can somebody explain why? Thanks
  15. N

    What materials stay unblemished after 1000s of centuries?

    I was wondering what materials will stay most unblemished after the 1000s of centuries of unforeseen wear such as corrosion, salt water, grinding, etc. Materials that are not very rare like gold or silver. I have looked into it and so far I've come across titanium, stainless steel, and their...
  16. T

    Galvanic corrosion of nickle copper alloys (nicopp, cunifer)

    what I'm doing. I'm trying to install copper-nickle brake lines but I'm trying to figure out what fitting to use. options are brass, steel, or stainless(which would fluctuate between active and passive given road salts, etc). I'm joining with aluminium and carbon steel and obviously...
  17. P

    Measuring pH on metallic planar surface

    We are currently trying to measure pH levels on the (wet) surface of metals as part of a study about corrosion. The surface may have a non-conductive protective layer. - is it feasible to measure pH on a planar surface (dry or wet)? Which kind of sensor probe can be used for this task? -...
  18. S

    Corrosion resistant material at high temperature/high pressure?

    Hi I am about to fabricate a part exposed to super critical water (600C & 250bar). In the past people have been using titanium or convoluted methods to prevent excessive corrosion induced by dissolved solids (principally Cl-), which under supercritical conditions precipitate, coming back into...
  19. M

    Gas Turbine & Psychrometric chart

    Hi Everyone, So I seem to have many problems understanding the Psychrometric chart and its physical meaning. First of all, I would be so thankful if you could introduce me a source which can be useful to physically and fundamentally understand the dew point, effect of pressure, humidity... and...
  20. S

    Corrosion mesurement techniques

    Hi guys i was wondering if there are methods available which allows one to measure corrosion that occurs in areas of materials where obvious defects exist like holes etc. Instead of using the conventional methods which measure uniform corrosion? Thank you in advance.
  21. D

    Calculating Corrosion Allowable Factor for SA516-70 Material?

    Dear all, I have one question about corrosion factor. How to find it? (may be have 1 table to determine it? ) thanks! N-Doan
  22. Priyank

    Corrosion of Magnesium: Reaction & Description

    1. In my Homework, the teacher gave me the project to collect the sample of corroded magnesium (pure metal, and not an alloy) and write a detailed description about the process related to it. 2. Although I collected the corroded sample, yet I am unable to write its description. What I know...
  23. P

    How does corrosion affect the resistivity of copper wire?

    I'm not sure if corrosion does have a significant effect on copper in general but if it does, how and why does it happen, and the process of it happening and its effect on the overall resistivity? This is for a physics assignment...Please help if you can. Thank you
  24. amrmohammed

    Corrosion in metal pipe carrying DC current?

    Hey Given the simple electric circuit below, the connection between the negative end of the DC source and the load (R1) is a pipe where heavy oil flow with some H2S and CO2. The pipe is made of iron and copper alloy. Without the DC current, H2S and CO2 will corrode the pipe. After introducing...
  25. D

    Problem with corrosion of gypsum cement

    Hi, I have been working on a formicarium (terrarium for ants) design for a while now, and have been battling a problem with what I think is corrosion of gypsum cement. This design has a hydration system that basically uses capillary action to wick water up a sponge and into gypsum cement...
  26. K

    Does Corrosion Transfer from Coated Materials to Others?

    I have tested stainless steel sample coated by a layer that claims to improve the hardness of the material without reducing corrosion resistance. After 72 hours of salt corrosion tests, I have found that there was corrosion. The corrosion was on the outside it did not travel beyond the coating...
  27. V

    Why my outboard carburetor corrosion?

    My 4 stroke outboard was sitting about 2-3 months, it couldn't start again last week. Then I disassemble the carburetor and want to clean it inside. But badly, lot of corrosion inside the carburetor. Can anyone tell me why it corrosion like this? because I store the outboard beside the sea...
  28. D

    How do you create pitted corrosion on steel with acid?

    Hi there, Wondering if anyone knows how to create pitting in steel with acid as the only method I know takes about 20 years and burying steel in the ground, not very ideal so was looking towards acid as I've heard of other people using it as an oxidizing agent to create corrosion on steel but...
  29. gracy

    Corrosion and Rust: What is Corrosion & Why Do New Layers Form?

    what corrosion really is?my teacher says it is disintegration and decaying of metals via chemical and more precisely redox reaction.so according to my teacher corrosion is the wearing away of a metal through a chemical reaction.my question is as corrosion is process of decaying,wearing away...
  30. coktail

    Homebrewing beer and galvanic corrosion

    I’ve started home brewing beer recently, and I’m assembling equipment for my first 5 gallon batch. The technique I’ll be using requires me to put grains into a nylon bag and then steep that bag of grains in hot water (approx 160°), much like a giant teabag. The trick is that the bag cannot touch...
  31. K

    Corrosion Vs Oxidation: Differences?

    Hi guys, Until now I thought that oxidation and corrosion are the same. But I am not sure. Are they one and the same? Why oxidation at high temperatures is important? How does that reduce part life? Thanks.
  32. R

    What are the potential dangers of using split flanges in process pumps?

    I was reading an accident report where a process pump leaked from its delivery line through a "split flange assembly". The report further mentions: "Split flanges are not a good feature because they expose twice as much surface to the effects of corrosion" What exactly is a split flange...
  33. WaterMelllon3

    Redox reaction formulas or corrosion formulas?

    I was just wondering if anyone has some redox reaction formulas or corrosion formulas? Cheers Darryl
  34. L

    Corrosion Engineering Degree | Scholarships in Oil/Gas

    Hi! I would like to ask if there is a university which offers a graduate degree in Corrosion engineering and have scholarships available? I am currently working as a Piping Materials Engineer in a Japanese company and I would like to pursue the field of corrosion engineering specially that it is...
  35. S

    Corrosion data using Electrochemistry

    Hi, I am a Chemical Engineer but a novice in electrochemistry; hence the query might sound very basic to everyone. We have an industrial electrochemical process (With Iron anode) and we are conducting a lab experiment to understand what is the effect of electrolyte pH on corrosion rate of...
  36. F

    Corrosion & pH: Explaining Observations of Iron Nail

    Homework Statement Hello guys. We are given a hypothetical data table and this is pretty much what it contains. It tells that when an iron nail is submerged in various aqueous solutions, the following observations were made. We are to give explanations to each why these things were observed...
  37. E

    Current increases rate of corrosion?

    Hi, This is my first post here, but I have searched this forum many times for insight. See the attached image. https://www.physicsforums.com/attachment.php?attachmentid=52558&stc=1&d=1351879807 The red loop is a metalic wire. The wire is expected to corrode when it is submersed into the...
  38. C

    Monitoring internal corrosion of a pipeline

    Hi All, I am wondering if there is any way to monitor internal corrosion in pipelines (without using pigs and interrupting the flow)? May be ultrasound waves could be used for this purpose, however I am not sure if it would be able to give a clear picture of extent of corrosion. Thanks...
  39. L

    Galvanic corrosion: trying to understand

    Hi, in the course of designing a heat exchanger for my company, I've ran into the problem of galvanic corrosion. I've managed to somehow figure out what to do to prevent it from happening, but I don't fully understand WHY. In other words, I don't have an exact feeling for what happens at the...
  40. N

    Engineering Best Corrosion engineering Phd programs

    Like the title of this thread suggests, I am wondering which Phd programs are the best in terms of corrosion engineering.
  41. G

    Does Iron Lose Mass When Exposed to Water and Oxygen?

    When iron corrodes in water, it loses electrons to oxygen and becomes iron ions. The oxygen retrieved the free electrons and along with water molecules formed hydroxide ions. Eventually, the iron ions and hydroxide ions react to form iron hydroxide. So based on this, would the iron loses mass...
  42. G

    Galvanic Corrosion: Anode vs. Cathode Mass Gain/Loss

    Homework Statement In Galvanic Corrosion, does the cathode gain mass, while the anode loses mass? Homework Equations The Attempt at a Solution The anode loses electrons to the cathode through the electrode. But i am not sure whether the cathode would gain mass or not. If so, when...
  43. S

    Change of pH in corrosion chamber

    Hi all. New to the forum & 1st post. I've recently been put in charge of using a corrosion chamber (Ascott 450+XP) in my place of work and I've not had much experience using them. We are validating the equipment to BS EN ISO 9227:2006 (pretty much exact same as ASTM B117) using steel...
  44. V

    Showing the corrosion of metals when placed in acid

    Homework Statement for a science experiment i am required to write relevant chemical equations to reactions that have occurred. I am having trouble showing the corrosion of iron, aluminum and copper in acetic acid and citric acid. Homework Equations heres what i have so far: Fe + 2...
  45. I

    Best undergrad field of study for a career in Corrosion engineering

    I am a non-traditional student (36 w/ a business degree after leaving a CHemE program when in school the first time). The last 12 years of my life, I have worked in the application of industrial coatings' to steel . I still work in the field, and will continue to. Now, I work in outside sales...
  46. streeters

    Engineering Somehow I've ended up a Corrosion engineer. Is this an ok field?

    I was chatting with my undergrad supervisor and they sorted out a PhD project for me doing corrosion science, split between my university and a synchrotron. Is corrosion a good field? I'm finishing a Materials Science degree and always pictured myself making alloys for a car or aircraft...
  47. J

    Corrosion Tests on Magnesium

    Hi all, So a little background. I am currently trying to characterize corrosion rates of AZ31B Magnesium [Mg-3%Al-1%Zn] which would be used as an implant within the coronary artery. Currently I'm running a static test of the magnesium in 0.9% NaCl(saline) in an incubator @37C. Im...
  48. J

    Understanding the Role of Ions in Corrosion of Metals in Aqueous Environments

    I have some questions concerning the tendency of a system containing two different metals and water to corrode. This is coming from several similar discussions on another forum, concerning water cooling of computer components. There seems to be a lot of repeated dogma, which may include...