Ch 10 Flashcards

1
Q

Define corrosion

A

Destructive attack of a metal by electro chemical interaction or chemical reaction with its environment

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2
Q

List the three conditions for corrosion

A

Oxidizing agent and Reducing agent

Must be thermodynamically favourable

Reaction occurs at surfaces of the material

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3
Q

What happens at the anode?

A

Oxidization

Loss of electrons

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4
Q

What happens at the cathode?

A

Reduction

Gain of electrons

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5
Q

What happens to oxidizing agents?

A

They’re reduced

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6
Q

What happens to reducing agents?

A

They’re oxidized

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7
Q

What is not typically involved in the cathode reaction for corrosion?

A

Metal ions

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8
Q

List the four components to an electrochemical cell, which all must be present for corrosion to occur

A

Anode

Cathode

Electrical connection

Electrolyte

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9
Q

What does the electrolyte do?

A

Conducts current via ions

Must be in contact with anode and cathode

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10
Q

How to stop corrosion

A

Remove one or more of the components from the electrochemical cell

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11
Q

Corrosion: what does passive mean?

A

Alloy forms, a protective layer

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12
Q

Corrosion: what does active mean?

A

When the alloy does not produce a protective layer

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13
Q

Why doesn’t stainless steel corrode

A

Because it corrodes very rapidly than forms, a protective layer, a very thin, inert metal oxide that prevents further reaction

For stainless steel the passive Cr2O3 layer forms

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14
Q

What does the galvanic series show

A

Inert and active

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15
Q

Define galvanic cell/composition cell

A

Galvanic corrosion occurs when dissimilar metals are connected and exposed to an electrolyte

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16
Q

Define stress cell

A

Stress area has a higher free energy and becomes the anode

17
Q

Define concentration cell

A

When it dissolves species involved in either the anode or cathode reaction varies in concentration at different locations in the electrolyte

Example: oxygen concentration cell

18
Q

Large cathode with small anode is what

And why

A

BAD

The surface area of the cathode is rather large compared to the anode so corrosion happens very fast

19
Q

List the three main types of electrochemical cells found in corrosion

A

Galvanic cell

Stress cell

Concentration cell

20
Q

List 5 methods for corrosion control

A

Coating

Inhibitors

Reduce dissolved oxygen

Galvanic protection

Reducing temperature

21
Q

Corrosion control: describe coating

A

Coating the surface to isolate it from the electrical light with paint or an electroplated layer of a noble metal

22
Q

Corrosion control: define inhibitors

A

Make adherent ions that coat the surface and isolated from the electro chemical reaction

23
Q

Corrosion control: define, reduce dissolved oxygen

A

Do this by either adding hydrazine to the water, or treating the water, using a hydrogen protection cell that replaces the oxygen in the water with hydrogen

24
Q

Corrosion control: define galvanic protection

A

Where are more and noticed metal is hooked up to the metal to be protected and dipped in the electrolyte

25
Q

Corrosion control: define reducing temperature

A

Higher temperatures increase the rate of chemical reactions