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Chemical Engineering 378

Science of Materials Engineering

Lecture 31Corrosion: Protection

Spiritual Thought2

“If it was right when you prayed about it and trusted it and lived for it, it is right now. Don’t give up when the pressure mounts. You can find an apartment. You can win over your mother-in-law. You can sell your harmonica and therein fund one more meal. It’s been done before. Don’t give in. Certainly don’t give in to that being who is bent on the destruction of your happiness. He wants everyone to be miserable like unto himself. Face your doubts. Master your fears. ‘Cast not away therefore your confidence.’ Stay the course and see the beauty of life unfold for you.”

- Elder Jeffery R. Holland

Materials Roadmap3

Corrosion Types4

Example5

Solution6

Solution (cont)7

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-- Use metals that passivate- These metals form a thin,

adhering oxide layer that slows corrosion.

• Lower the temperature (reduces rates of oxidation and reduction)

CORROSION PREVENTION (I)

Metal (e.g., Al, stainless steel)

Metal oxide

• Apply physical barriers -- e.g., films and coatings

• Materials Selection-- Use metals that are relatively unreactive in the corrosion environment -- e.g., Ni in basic solutions

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Passivation

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Passivation (cont)

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Anodic Protection

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Passivation (cont)

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Oxide Layers

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CORROSION PREVENTION (II)

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CORROSION PREVENTION (III)

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Protective Layers

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Inhibitors

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Best Practices (welding)

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CORROSION PREVENTION (ii)• Cathodic (or sacrificial) protection

-- Attach a more anodic material to the one to be protected.-- Apply a current

steel

zinczinc

Zn 2+

2e - 2e -

e.g., zinc-coated nail

Galvanized Steel Using a sacrificial anode

steel pipe

Mg anode

Cu wiree-

Earth

Mg 2+

e.g., Mg Anode

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SACRIFICIAL ANODE

Chemical Engineering 378��Science of Materials Engineering��Spiritual ThoughtMaterials RoadmapCorrosion TypesExampleSolutionSolution (cont)CORROSION PREVENTION (I)Slide Number 9Slide Number 10Slide Number 11Slide Number 12Slide Number 13CORROSION PREVENTION (II)Slide Number 15Slide Number 16Slide Number 17Slide Number 18Slide Number 19CORROSION PREVENTION (ii)Slide Number 21