Corrosion E5 study material

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Corrosion E5 study material
2013-11-18 02:24:22

Chapter 3 Study material
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  1. Define corrosion.
    Corrosion is the electrochemical deterioration of a material or its properties due to its chemical reaction with the surrounding environment
  2. What is an atom?
    The smallest unit of an element, made up of a positively charged nucleus surrounded by a system of negatively charged electrons.
  3. What is an electron?
    A negatively charged subatomic particle. An electric current occurs when electrons are forced to move through metal conductors.
  4. What is electrolyte?
    A liquid (usually water) solution containing ions.
  5. Define the theory of corrosion
    All metals will corrode to some extent in a natural environment.
  6. What is the best time to prevent corrosion?
    At the design stage. Proper material selection is critical for the protection of equipment against harmful environmental effects.
  7. What are dissimilar metals and how do they affect corrosion?
    When two dissimilar metals make electrical contact in the presence of an electrolyte, the rate at which corrosion occurs depends on the difference in their activities.
  8. What does anode and cathode surface area affect in corrosion?  
    The rate of corrosion also depends on the size of the parts in contact. Big anode + small cathode = Fast corrosion, Small anode + large cathode = slow corrosion.
  9. How does temperature affect corrosion?
    Higher temperature environments tend to produce more rapid corrosion.
  10. How do biological organisms affect corrosion?
    Bacteria’s, molds, fungi, and other living organisms can grow on damp surfaces. Once established, the area tends to remain damp, increasing the possibility of corrosion.
  11. How does length of exposure affect corrosion?
    Metals naturally corrode over time. Sometimes the corrosion is at the same rate no matter how long the metal has been exposed, in others it decreases with time due to the barrier formed by corrosion products, or increases if a barrier to corrosion is broken down.
  12. What is uniform surface corrosion?
    Uniform surface corrosion is the most common type of corrosion. It results from a direct chemical attack on a metal surface that proceeds uniformly over the entire exposed surface.
  13. What is galvanic corrosion?
    Galvanic corrosion is when different metals contact each other and an electrolyte. Usually recognizable by a buildup of corrosion at the joint between them.
  14. What is pitting corrosion?
    Pitting is a form of extremely localized attack that results in holes in the metal.
  15. What is intergranular corrosion?
    Intergranular corrosion is an attack on the grain boundaries of the metal. Think wood grain.
  16. What is exfoliation corrosion?
    Exfoliation is an advanced 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. Think peeling paint.
  17. What is crevice corrosion?
    Liquids in the crevice/cracks of metal.
  18. What is Filiform corrosion?
    Filiform corrosion is a form of crevice corrosion which occurs on metal surfaces having a thin organic protective coating. It is looks like wormlike trace of corrosion.
  19. What is erosion corrosion?
    Erosion corrosion is the increase in the rate of attack on a metal due to the action of a corrosive fluid against the metal surface.
  20. What is stress corrosion?
    Stress corrosion  is the combined effects of constant tensile stress and corrosion.
  21. What is corrosion fatigue?
    Corrosion fatigue is the cracking of metals caused by the combined effects of cyclic stress and corrosion.
  22. What is fretting corrosion?
    Fretting corrosion occurs at contact areas between materials under load subject to repeated vibration.
  23. What is hot corrosion?
    Also called high temperature oxidation. Corrosion in the absence of water can occur at high temperatures.
  24. What color is aluminum corrosion?
    White to grey powdery material
  25. What color is magnesium corrosion?
    White powdery snow like mounds
  26. What color is steel corrosion?
    Reddish-brown oxide (rust)
  27. What color is nickel corrosion?
    Green powdery deposit
  28. What color is copper corrosion?
    Blue or blue-green powdery deposit
  29. What color is silver corrosion?
    Brown to black film
  30. What color is gold corrosion?
    Deposits cause darkening of reflective surfaces
  31. What is the degradation of non-metals?
    Nonmetallic materials are not subject to electrochemical corrosion, because ions do not easily pass through them, but depending on their composition will eventually degrade/corrode.
  32. Define Graphite/Carbon fiber composites.
    Graphite or carbon fiber composites are materials made of reinforcing fibers in organic resin, usually epoxy. They are an important materials because of their high strength-to-weight ratios and high stiffness.
  33. How do salt atmospheres affect corrosion?
    Salt forms a strong electrolyte when dissolved in water, which causes rapid corrosion of unprotected metal surfaces.
  34. How do climates affect corrosion?
    Warm, moist air, normally found in tropical climates, tends to accelerate corrosion. Cold, dry air, normally found in arctic climates, tends to reduce corrosion rates.
  35. How do tropic climates affect corrosion?
    Worst place, Heat +  Moisture = No good.
  36. What is solder flux corrosion?
    The simple task of soldering a component in a circuit board can cause corrosion, often due to failure to remove flux residues.
  37. What does seal deterioration have to do with corrosion?
    Fixed-wing and rotary-wing aircraft have some airframe flexibility, which results in seal deterioration. This allows moisture/fluid intrusion.