Material Selection Quiz 9

How can you tell whether a metal will corrode?

electrode potential and Pourbaix diagram

How can you know how fast a metal will corrode?

corrosion current density and Faraday’s Law

In dry air, an ______ film forms that ions must diffuse through

oxide

In a wet environment, corrosion is an electrochemical reaction, with ions moving through the ____ and electrons through the ______. Does the corrosion product form on or away from the metal?

liquid, metal, away

Which is faster, wet or dry corrosion?

wet

the ______ gives up electrons and ions (is what corrodes), the _____ recieves electrons

anode, cathode

metal connecting anode and cathode

electronic path

electrolyte carrying ions between cathode and anode

ionic path

Metal is _____ at the anode and ______ at the cathode

oxidized, reduced

If the electrode potential is more _____ then it gives up electrons more easily, but if its more ______ it accepts electrons more easily

negative, positive

What value do you use to place metals on the galvanic series?

open-circuit potential

A Pourbaix diagram is an electrochemical phase diagram of _____ vs. ____ for a metal in an aqueous solution showing which species is stable

potential, pH

What are the three phases in a Pourbaix diagram?

immunity (no corrosion), corrosion (metal dissolves), passivation (a film can form)

Connecting 2 different metals in an electrolyte forms a _____ couple

galvanic

In a galvanic couple, the anode’s current density depends on the ____ of the two metals

areas (Ac/Aa)

In a galvanic couple, a small anode paired with a large cathode results in a ____ attack on the anode

fast

In a couple the ____ (more/less) oxygen-rich region is the anode

less

Methods of corrosion protection:

1. Passivating alloy (Cr, Al) - forms a protective film that self-heals and prevents ____ attack

2. Barrier coating (paint, noble metal) - blocks the _____ and prevents flowing through ionic path

3. Sacrificial anode, galvanizing - makes the protected metal the _____

anode, electrolyte, cathode