Slide 1
Common metal corrosion links chemical and electrical reactions
Corrosion degrades a material through interaction with the environment. Much common metal corrosion proceeds through coupled electrochemical reactions.
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The process needs places where oxidation and reduction occur, with paths for electrons and ionic charge. Interrupting one of those paths can slow or prevent the overall corrosion circuit.
Slide 2
Different local conditions can form a corrosion cell
Different metals, or different conditions on one metal, can create corrosion cells. Moisture with dissolved ions can act as an electrolyte: a liquid path for electrical charge.
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A crevice can develop chemistry unlike the exposed surface nearby. Damage may then concentrate in a small hidden region rather than spreading uniformly across the visible area.
Slide 3
Connected metals can corrode unequally in an electrolyte
Dissimilar metals connected in an electrolyte can undergo galvanic corrosion. The more active partner can corrode preferentially under those conditions.
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The relative exposed areas matter: a small anodic area connected to a large cathodic area can suffer intense local attack. A materials list alone therefore does not fully describe the risk.
Slide 4
A barrier blocks access; a sacrificial metal corrodes instead
A coating can block environmental access. A sacrificial metal can instead corrode preferentially to protect the component connected to it.
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A scratched barrier coating may expose a vulnerable small area, while an appropriate sacrificial coating can provide some electrochemical protection at damage. Their responses to defects are therefore different.
Slide 5
Geometry and maintenance must suit the actual exposure
Drainage, compatible materials and inspection access help control corrosion. Protection must suit the temperature, chemistry and wetting conditions.
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A sheltered pocket that retains water can defeat an otherwise sensible material choice. Geometry and maintenance therefore join chemistry in determining how long the component remains serviceable.