SUMMARY:
CORROSION AND MATERIAL
DEGRADATION
By Claudia B. N.
, Examples of materials in a state of HIGHER
INTRODUCTION TO CORROSION ENERGY:
CORROSION → occurs in metals and alloys. • steel profiles
• copper cables
DEGRADATION → occurs in plastics,
• galvanized steel sheets
ceramics, composite materials, and
semiconductors. WHAT PROBLEMS DOES METAL
CORROSION CAUSE?
Minerals are in a state of STABILITY because
they are in a state of LOWER ENERGY. They • Structures with poor appearance.
are found in the Earth's crust (oxides, • Possible premature failures.
sulfides, carbides, etc.). On the other hand, • Service interruptions.
metals obtained through the processing of
minerals and mines will enter a state of HOW MUCH DOES IT COST TO COMBAT
INSTABILITY, that is, a state of HIGHER METAL CORROSION?
ENERGY. • The economic losses generated by
Corrosion is defined as the deterioration of a corrosion worldwide amount to 3-5%
material as a result of electrochemical of GDP.
attack by its environment. • In Peru, this amounts to
approximately $5.7-9.8 billion
Corrosion can be understood as the general annually.
tendency of materials to seek their most
stable form or lowest internal energy state. HOW TO REDUCE THE COSTS GENERATED
BY CORROSION?
Education on the corrosive phenomenon
and control methods to save between 25
and 30% of this cost.
DRIVING FORCE OF CORROSION.
It is a problem caused by nature that affects
materials and is governed by changes in
energy:
Corrosion is an ELECTROCHEMICAL
PHENOMENON, due to the fact that a) Energy cannot be created or destroyed.
electrons are emitted during oxidation ∆𝐺 = −𝑛𝐹𝐸 = 𝑊𝑒𝑙é𝑐𝑡𝑟𝑖𝑐𝑎
reactions, which causes an electric current
∆𝐺 = (−) → 𝐸𝑠𝑝𝑜𝑛𝑡á𝑛𝑒𝑎
to flow.
b) All spontaneous changes occur with a
Examples of minerals in a state of LOWER
release of free energy from the
ENERGY:
surrounding system at constant
• magnetite and hematite temperature and pressure.
• chalcopyrite
• zinc blende
,"Since corrosion occurs in nature, it will be VELOCITY OF A CORROSION REACTION (v)
spontaneous, or there will be a release of
𝑉 = 𝑘𝑐𝑜𝑟𝑟 [𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠]
energy.”
Where:
ELECTROCHEMICAL REACTIONS
• [𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠]: is a measure of the
amount of substance transported.
• 𝑘𝑐𝑜𝑟𝑟 : is the reaction rate constant.
• ∆𝐺 (free activation energy) is the
∗
• 𝑘𝑐𝑜𝑟𝑟 = 𝐴 exp (−∆𝐺 ∗ /𝑅𝑇)
minimum energy required for
METALS THAT DO NOT CORRODE UNDER
reactants to convert into products.
ENVIRONMENTAL CONDITIONS
• ∆𝐺 is the change in free energy from
reactants to products. • Gold
• ∆𝐺 is a state function, therefore it is • Silver
independent of the form or path • Platinum
followed for the transformation.
* However, in aqua regia (HNO2 and HCl) it
• ∆𝐺 reflects only the direction of the
does occur (acidic medium).
reaction.
• If ∆𝐺 is negative (-), it indicates that Example:
the reaction is spontaneous and
• Oxidation:
irreversible (energy is being
𝐴𝑢 → 𝐴𝑢2 + 3𝑒 −
released).
• Reduction:
2𝐻 + + 2𝑒 − → 𝐻2 (𝑔)
This is because the energy conditions may
be unfavorable. If the conditions are
favorable, ∆𝐺 is so large that it does not
reach.
More examples:
When comparing two elements with respect
to their E, the one closest to zero (0) is the THERMODYNAMIC ASPECTS OF
one with the HIGHEST RESISTANCE to ELECTROCHEMICAL CORROSION
CORROSION.
Calculation of the change in free energy
ELECTROCHEMICAL POTENTIAL during the corrosion process for a specific
Lower corrosion temperature:
𝐴𝑙 → 𝐸 = −1.60𝑉 →
resistance
∆𝐺 = ∆𝐺° + 𝑅. 𝑇. 𝑙𝑛𝐽
Higher corrosion
𝐹𝑒 → 𝐸 = 0.44𝑉 → resistance
, Where: Electrochemical Corrosion Cell
• ∆G: Change in free energy at any It has four components:
temperature
• ∆Gº: Change in free energy under • Anode
standard conditions • Cathode
• R: Universal gas constant • Electrolyte
• T: Absolute temperature • Electrical connection
• J: Mass action constant
FARADAY'S LAW
∆G can also be expressed in terms of
Faraday (F), the number of electrons
exchanged (n), and the potential at which the
process takes place (E):
∆𝐺 = −𝑛𝐹𝐸
∆𝐺° = −𝑛𝐹𝐸°
DOES A PURE METAL HAVE ANODIC AND
General reaction: CATODIC ZONES?
Yes! In its solid state, it has regular zones
(grain body) and irregular zones (grain
∆𝐺 = ∆𝐺° + 𝑅. 𝑇. 𝑙𝑛[𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠]/[𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠] boundaries).
Substituting the following equations: DOES AN ALLOY HAVE ANODIC AND
CATHODIC ZONES?
∆𝐺 = −𝑛𝐹𝐸 , ∆𝐺° = −𝑛𝐹𝐸
Yes, it does, because it has different phases
End up with: in addition to grains and grain boundaries.
𝑅𝑇 [𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠]
𝐸 = 𝐸° − . ln
𝑧𝐹 [𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠]
NERNST EQUATION
HOW DOES AQUEOUS METAL
CORROSION OCCUR?
The corrosive phenomenon occurs in the
same way as the operation of a short-
circuited galvanic cell.
CORROSION AND MATERIAL
DEGRADATION
By Claudia B. N.
, Examples of materials in a state of HIGHER
INTRODUCTION TO CORROSION ENERGY:
CORROSION → occurs in metals and alloys. • steel profiles
• copper cables
DEGRADATION → occurs in plastics,
• galvanized steel sheets
ceramics, composite materials, and
semiconductors. WHAT PROBLEMS DOES METAL
CORROSION CAUSE?
Minerals are in a state of STABILITY because
they are in a state of LOWER ENERGY. They • Structures with poor appearance.
are found in the Earth's crust (oxides, • Possible premature failures.
sulfides, carbides, etc.). On the other hand, • Service interruptions.
metals obtained through the processing of
minerals and mines will enter a state of HOW MUCH DOES IT COST TO COMBAT
INSTABILITY, that is, a state of HIGHER METAL CORROSION?
ENERGY. • The economic losses generated by
Corrosion is defined as the deterioration of a corrosion worldwide amount to 3-5%
material as a result of electrochemical of GDP.
attack by its environment. • In Peru, this amounts to
approximately $5.7-9.8 billion
Corrosion can be understood as the general annually.
tendency of materials to seek their most
stable form or lowest internal energy state. HOW TO REDUCE THE COSTS GENERATED
BY CORROSION?
Education on the corrosive phenomenon
and control methods to save between 25
and 30% of this cost.
DRIVING FORCE OF CORROSION.
It is a problem caused by nature that affects
materials and is governed by changes in
energy:
Corrosion is an ELECTROCHEMICAL
PHENOMENON, due to the fact that a) Energy cannot be created or destroyed.
electrons are emitted during oxidation ∆𝐺 = −𝑛𝐹𝐸 = 𝑊𝑒𝑙é𝑐𝑡𝑟𝑖𝑐𝑎
reactions, which causes an electric current
∆𝐺 = (−) → 𝐸𝑠𝑝𝑜𝑛𝑡á𝑛𝑒𝑎
to flow.
b) All spontaneous changes occur with a
Examples of minerals in a state of LOWER
release of free energy from the
ENERGY:
surrounding system at constant
• magnetite and hematite temperature and pressure.
• chalcopyrite
• zinc blende
,"Since corrosion occurs in nature, it will be VELOCITY OF A CORROSION REACTION (v)
spontaneous, or there will be a release of
𝑉 = 𝑘𝑐𝑜𝑟𝑟 [𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠]
energy.”
Where:
ELECTROCHEMICAL REACTIONS
• [𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠]: is a measure of the
amount of substance transported.
• 𝑘𝑐𝑜𝑟𝑟 : is the reaction rate constant.
• ∆𝐺 (free activation energy) is the
∗
• 𝑘𝑐𝑜𝑟𝑟 = 𝐴 exp (−∆𝐺 ∗ /𝑅𝑇)
minimum energy required for
METALS THAT DO NOT CORRODE UNDER
reactants to convert into products.
ENVIRONMENTAL CONDITIONS
• ∆𝐺 is the change in free energy from
reactants to products. • Gold
• ∆𝐺 is a state function, therefore it is • Silver
independent of the form or path • Platinum
followed for the transformation.
* However, in aqua regia (HNO2 and HCl) it
• ∆𝐺 reflects only the direction of the
does occur (acidic medium).
reaction.
• If ∆𝐺 is negative (-), it indicates that Example:
the reaction is spontaneous and
• Oxidation:
irreversible (energy is being
𝐴𝑢 → 𝐴𝑢2 + 3𝑒 −
released).
• Reduction:
2𝐻 + + 2𝑒 − → 𝐻2 (𝑔)
This is because the energy conditions may
be unfavorable. If the conditions are
favorable, ∆𝐺 is so large that it does not
reach.
More examples:
When comparing two elements with respect
to their E, the one closest to zero (0) is the THERMODYNAMIC ASPECTS OF
one with the HIGHEST RESISTANCE to ELECTROCHEMICAL CORROSION
CORROSION.
Calculation of the change in free energy
ELECTROCHEMICAL POTENTIAL during the corrosion process for a specific
Lower corrosion temperature:
𝐴𝑙 → 𝐸 = −1.60𝑉 →
resistance
∆𝐺 = ∆𝐺° + 𝑅. 𝑇. 𝑙𝑛𝐽
Higher corrosion
𝐹𝑒 → 𝐸 = 0.44𝑉 → resistance
, Where: Electrochemical Corrosion Cell
• ∆G: Change in free energy at any It has four components:
temperature
• ∆Gº: Change in free energy under • Anode
standard conditions • Cathode
• R: Universal gas constant • Electrolyte
• T: Absolute temperature • Electrical connection
• J: Mass action constant
FARADAY'S LAW
∆G can also be expressed in terms of
Faraday (F), the number of electrons
exchanged (n), and the potential at which the
process takes place (E):
∆𝐺 = −𝑛𝐹𝐸
∆𝐺° = −𝑛𝐹𝐸°
DOES A PURE METAL HAVE ANODIC AND
General reaction: CATODIC ZONES?
Yes! In its solid state, it has regular zones
(grain body) and irregular zones (grain
∆𝐺 = ∆𝐺° + 𝑅. 𝑇. 𝑙𝑛[𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠]/[𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠] boundaries).
Substituting the following equations: DOES AN ALLOY HAVE ANODIC AND
CATHODIC ZONES?
∆𝐺 = −𝑛𝐹𝐸 , ∆𝐺° = −𝑛𝐹𝐸
Yes, it does, because it has different phases
End up with: in addition to grains and grain boundaries.
𝑅𝑇 [𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠]
𝐸 = 𝐸° − . ln
𝑧𝐹 [𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠]
NERNST EQUATION
HOW DOES AQUEOUS METAL
CORROSION OCCUR?
The corrosive phenomenon occurs in the
same way as the operation of a short-
circuited galvanic cell.
