lectures on corrosion dehradation slides

corrosion degradation lecture good slides

1. Degradation of Materials
Why are we interested in degradation?
It’s important to analyze how materials are affected
by environment
Design:
Consider unintended and excessive load
Unintended environmental effects
Identifying instances where stress and environment play
a synergistic role in degrading materials

2. Degradation of Materials
Corrosion
Many metals are susceptible to oxidation and
corrosion.
Consider: Half Cell Reactions and Cell
Potentials
Anode, Anode reaction (oxidation)
Cathode, Cathode reaction (reduction)
Deterioration can be both unsightly and unsafe
if design load decreases due to material loss

3. Degradation of Materials
Corrosion testing
I-V Curves (Anodic Polarization Curves)
Current/Voltage measurements associated with
electron flow
Weight Loss Measurements in environment
(Corrosion Penetration Rates)
Time dependent weight loss measurements in
environment

4. Degradation of Materials
Forms of Corrosion
Uniform Corrosion as a layer
Galvanic Corrosion: Battery cell between different
metals
Morphologically influenced corrosion:
Intergranular Corrosion (corrosion on grain boundaries)
Pitting Corrosion
Leaching of a susceptible element from an alloy
Many combination mechanisms

5. Degradation of Materials
Corrosion Prevention
Passivation layers (oxides)
Sacraficial Anodes as a means of protecting a
more expensive material construct
Paint, Primers, etc.
For a corroding layer, if forming an oxide, we
can look at Pilling-Bedwith ratios as a gauge
of oxide coverage
Mass gain...not mass loss necessarily

6. Degradation of Materials
P-B Ratios
IF ratio is less than 1, oxide has poor coverage
and will not insulate metal from further
corrosion
If greater than 1, compressive stresses result
from the formation of the oxide, which can
stress the interface and lead to spalling
(removal) of the oxide layer