Basic Principles of Corrosion Knowledge

1. SINERGY – Safety, health & environment – INnovative – profEssional – integRity – diGnitY

2. “Why study corrosion…???”
Introduction to
Corrosion

3. WHY…?
Materials are precious resources of a country
Engineering knowledge is incomplete without
an understanding of corrosion
Corrosion has been a very important factor in
several engineering disasters
Corrosion is a threat to the environment
Introduction to
Corrosion

4. “What does it look like…?
“When do you know if you have it…?
Introduction to
Corrosion

5. “What does it look like…?
Introduction to
Corrosion

6. What is
Corrosion…?
SINERGY – Safety,
health & environment –
INnovative –
profEssional – integRity
– diGnitY
Corrosion is the deterioration of materials by chemical
interaction with their environment

7. – Metal, logam (besi, aluminium, seng, dll )
– Nonmetallic Materials (Plastic, Rubber, ceramics,
concrete )
– Deterioration of paint and rubber by sunlight or
chemicals
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Material

8. • Umumnya segala lingkungan adalah korosif
sesuai tingkatannya.
• Contoh :
waters (fresh, distilled, salt, mine waters)
Atmospheres (rural, urban, and industrial
atmospheres)
Gases (chlorine, ammonia, hydrogen sulfide,
sulfur dioxide, and fuel gases)
Mineral acid ( hydrochloric, sulfuric, nitric)
Soils
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Lingkungan

9. BARANG JADI
EKSTRAKSI
DAN
PENGERJAAN
PERUSAKAN
DAN KOROSI
BIJIH
Corrosion is a
natural
process…!
Steel
Making
Goods
Corrosion
Ore

10. Consequences of
Corrosion…
Plant shutdowns
Loss of products
Loss of efficiency
Contamination
Nuclear hazards
Consequences

11. Aspects of
Corrosion
• Impermeability:
• Mechanical strength:
• Dimensional integrity:
• Physical properties
• Contamination
• Damage to equipment
Function
al Aspect
•Safety: Sudden failure can cause explosions and fire, release of
toxic products and collapse of structures
•Health: Adverse effects on health may be caused by
corroding structures
•Depletion of resources
•Appearance and cleanliness:
•Product Life: Corrosion seriously shortens the predicted
design life
SHE and
Product
Life

12. Factors Affecting
the Corrosion
SINERGY – Safety,
health & environment –
INnovative –
profEssional – integRity
– diGnitY
Corrosion
Resistance
Metallur
gical
Chemical
Environ
ment
Thermod
ynamicall
y
Physical

13. Corrosion of
Metals
 Metal is extracted from ore (using considerable energy) and
then used as metal or alloy.
 But as metal are usually in higher energy state, more
favorable energetically to reform oxides etc.
Occasionally corrosion process is useful;
 Aluminum oxide (anodizing)
 Etching of microstructures
 Dry-cell batteries
BUT usually it is undesirable….

14. Corrosion
Mechanism
Corrosion of metals
Oxidation – reduction process take place and metal atoms
lose electrons (become ions) and go into solution.
Often occurs in aqueous medium where moisture can
provide electrical circuit to form an electrochemical
cell

15. Electrochemical
Cell
The overall electrochemical reaction consist of at least one oxidation
reaction (half-reaction) and at least one reduction reaction (half-
reaction)
Anode Cathode
Electrolyte
Conductor
 Anode gives up electrons to the
circuit and corrodes.
 Cathode receives electrodes
 The anodes and cathodes must
be electrically connected
 A liquid electrolyte must be in
contact with the anode and
cathode to complete the circuit
and allow movements of the
ions.

16. Oxidation Reaction
Oxidation – occurs at the ANODE  corrosion
(dissolving)  produces electrons
Metals  Ions
M  Mn+ + ne-
Zn  Zn2+ + 2e-
Na  Na + e-
Fe  Fe 2+ + 2e-
Electrons transferred to another chemical
reaction - Reduction

17. Reduction
Reaction
Reduction reactions occurs at the cathode
 Cathodic Reaction  consume electrons
If H+ ions
available 2H++2e-  H2
If acid solution
with dissolved
oxygen
O2+4H++4e-  2H2O
If basic/neutral
with dissolved
oxygen
O2+2H2O+4e-  4(OH-)

18. Anode Cathode
Corrosion
Reactions…
Ionic – Current
Path
Electronic Path

19. Corrosion is an Electrochemical Reactio
 Two different reactions occur - oxidation and
reduction
 Electron transfer occurs
 Potential (voltage) driving force required
 Oxidation occurs at anode
 Reduction occurs at cathode
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20. Mekanisme Korosi
Syarat terjadinya proses korosi :
1. anoda, terjadi reaksi oksidasi,
2. katoda, terjadi reaksi reduksi
3. elektrolit, penghantar arus listrik
4. ada hubungan anoda dengan katoda
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21. Corrosion Cells..
• Galvanic Cells  dissimilar metals in an
electrolyte or the same metal in dissimilar
conditions in a common electrolyte
• Concentration Cells  the same metal in
heterogeneous electrolyte
• Electrolytic Cells  external current is
introduced into the system
• Differential Temperature Cells

22. Rusting of Iron by water
droplet…
RUST!!!

23. Corrosion of Zinc in
Acid…
Zinc Acid Solution
Zn Zn2+
H+
H+
H+
H+
H+
Flow of e-
In the metal
H2 (gas)
2e+
Zn Zn2+
Reduction reaction
Oxidation reaction
Two reactions are necessary;
 Oxidation reaction: Zn  Zn2+ + 2e-
 anodic reaction
 Reduction reaction: 2H+ + 2e-  H2 (gas)
 cathodic reaction

24. Electrode Potential
A voltage difference of 0.78V is
associated with this reaction
 For perfect metal in an electrolyte, an
Electrode Potential is developed which
is related to the tendency of the metal
to give up electrons (oxidize).
 Different metals have different
tendencies to be oxidized.
 Iron electrode will dissolve (oxidize)
Fe  Fe2+ + 2e-
 Copper electrode will grow
(electroplate – Cu2+ be reduced)
Cu2+ + 2e-  Cu
V
0.780 V
- +
Membrane
Fe Cu
Cu2+
Fe2+
Fe2+ solution
1.0 M
Cu2+ solution
1.0 M
Anode Cathode
e-
e-
Voltmeter
Example: Iron and Copper

25. Electrode Potential
V
0.323 V
+ -
Membrane
Fe Zn
Zn2+
Fe2+
Fe2+ solution
1.0 M
Zn2+ solution
1.0 M
Cathode Anode
e-
e-
Voltmeter
An electrode potential/voltage exists
between two cell halves; varies with
metals
GALVANIC COUPLE; Iron and Zinc
 Iron plates out (iron ions are reduced)
 Zinc electrode dissolves (oxidizes)
Note: This cell has a different
voltage to the Fe- Cu cell

26. Electrode Potential
Concept of Electronegativity
 Electronegativity is a measure of the degree to which an atom attracts a
free electron.
 If 2 metals are in contact (either by way of an electrolytic solution or a
wire), they will exchange electrons, according to their electronegativity
difference.
 There will be a net flow of electrons from the more electropositive
(anode) to the electronegative (cathode) metal.

27. Electrode Potential
 The electrode potential for a particular metal (driving force for oxidation –
reduction reaction) cannot be measured by itself – need a reference
electrode to compare it with.
 To get an idea of tendencies to corrode, measure voltage produced by
metal reaction, with standard voltage of a reference cell.

28. Standard
Electromotive Force
(EMF)
V
Membrane
H+ solution
1.0 M
Hydrogen gas,
1 atm pressure
Pt
Voltmeter
Pt does not take part in the electrochemical reaction; it acts only as surface
on which hydrogen atoms may be oxidized or hydrogen ions may be
reduced
Reference Cell  Hydrogen electrode
H2  2H+ + 2e- or vice versa
2H+ + 2e-  H2
Assigned zero voltage, V0
So reaction with metal:
Compare this voltage with standard

29. Standard Hydrogen (EMF)
test
V
Metal (M1) mass
+ -
M1 Pt
H+
M1n+
M1n+ solution
1.0 M
H+ solution
1.0 M
e-
e-
ions
ne-
H+ 2e-
25oC
Metal (M1) is the cathode (+)
V0
M1 > 0 (relative to Pt)
V
Metal (M2) mass
- +
Pt
H+
M2n+
M2n+ solution
1.0 M
H+ solution
1.0 M
e-
e-
M2
ions
ne-
H+
H2 (gas)
2e-
25oC
Metal (M2) is the anode (-)
V0
M2 < 0 (relative to Pt)
V0
M1 and V0
M2  Standard Electrode Potential

30. EMF Series…
Electrode Reaction Standard Electrode
Potential, V0 (V)
Au3+ + 3e-  Au + 1.420
O2 + 4H+ + 4e-  2H2O + 1.229
Pt2+ + 2e-  Pt + 1.2
Ag+ + e-  Ag + 0.800
Fe3+ + e-  Fe2+ + 0.771
O2 + 2H2O + 4e-  4(OH-) + 0.401
Cu2+ + 2e-  Cu + 0.340
2H+ + 2e-  H2 0.000
Pb2+ + 2e-  H2 - 0.126
Sn2+ + 2e-  Sn - 0.136
Ni2+ + 2e-  Ni - 0.250
Co2+ + 2e-  Co - 0.277
Cd2+ + 2e-  Cd - 0.403
Fe2+ + 2e-  Fe - 0.440
Cr3+ + 3e-  Cr - 0.744
Zn2+ + 2e-  Zn - 0.763
Al3+ +3e-  Al - 1.662
Mg2+ + 2e-  Mg - 2.363
Na2+ + e-  Na - 2.714
K+ + e-  K - 2.924
Increasingly Inert
(Cathodic)
Increasingly active
(anodic)
 Anything above Fe+
 cathode relative to iron
 Anything below Fe+
 anode relative to iron
These are for reduction reaction;
For oxidation reaction the
direction of the reaction is
reversed and the sign of the
voltage changed.
Cu  Cu2+ + 2e- V0 = -0.340V

31. Relative Corrosion
Potential
The Galvanic Series
Platinum
Gold
Graphite
Titanium
Silver
316 SS (passive)
304 SS (passive)
Inconel (passive)
Nickel (passive)
Monel
Copper – nickel alloys
Bronzes
Copper
Brasses
Inconel (active)
Nickel (active)
Tin
Lead
316 SS (active)
304 SS (active)
Cast Iron
Iron and Steel
Aluminum Alloys
Cadmium
Commercially Pure Aluminum
Zinc
Magnesium and Mg Alloys
Increasingly Inert
(Cathodic)
Increasingly active
(anodic)
Metal ranked according to their tendency to
corrode in seawater.
 Metal near the top are highly cathodic
 resist corrosion and accept electrons)
 Metal near the bottom corrode rather easily
 source of electrons
 If metal “A” falls below metal “B” on this list.
“A” will most likely corrode and eventually
disintegrate when electrically connected to
“B”

32. Electrolytic Corrosion
within a Single Piece of
Metal
• Variations within the metal structure can result in
different electrode potentials at different points on
the surface
• Steel corrosion is accelerated by the presence of
salts – increases the conductivity of the electrolyte -
aids the flow of ions in solution
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33. Cause Anode Examples Rectify
Grain structureGrain boundary Steel/damp Isolate steel
Concentration Low Soil types Protective coatings
variations in concentration
electrolyte areas
Differential Oxygen remote Underground Protective coatings
aeration areas steel pipes
Stressed areas Most heavily Steel rivets Protect from
stressed area or nails dampness
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Cause of Corrosion

34. • A steel surface consists of noble and less noble areas
• This can be looked upon as small galvanic cells
• The anodic parts will corrode
+
+
+
+
-
-
-
+
-
-
+
-
+
+
-
+
Rust
+
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35. SUMBER HETEROGENITAS
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36. BUTIRAN HALUS = ANODIK
BUTIRAN KASAR = KATODIK
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37. TERBENTUKNYA
DAERAH ANODIK
DAERAH DIMANA ADA TEGANGAN SISA KARENA
PENGERJAAN DINGIN (PEMBENGKOKAN, PEMUKULAN, PENGELASAN, DLL.
ANODIK
37

38. BAGIAN YANG
LEBIH PANAS
(ANODIK) AKAN
TERKOROSI
T
38

39. Differential Aeration Cells
O2
O2
Karat + H2O
Baja
K K
e e
A
Baja
Dilut
e
NaCl
Udar
a
O2
O2
Kara
t
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