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ME 230: Control Of Properties Of Materials > Corrosion > Flashcards

Corrosion Flashcards

1
Q

What is an electrochemical reaction

A

A reaction which involves charge transfer (electro) and formation of a new compound from chemical elements

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2
Q

What is required for charge transfer to occur and what functions to fill this requirement

A

Charge transfers requires a charge carrier
+ve → ions
-ve → electrons

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3
Q

(T/F) metal ions do not act as a charge carrier for positive charge

A

F

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4
Q

(T/F) In an electrochemical cell, something losses change and something gains charge

A

T

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5
Q

Parts of an electro chemical cell

A

1) electrodes → anode, cathode
2) electrolyte: solution where electrical conduction is carried out by ions
3) electrical contact→ wire

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6
Q

Anode____ electrons, cathode ___ electrons

A

Losses, gains

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7
Q

Anode = ___. Cathode=____

A

Oxidization, reduction

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8
Q

What can be an electrolyte

A

Any thing that allows the flow of ions

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9
Q

What can be an electrical contact

A

Any thing that allows electrons to flow (current)

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10
Q

How much of an electrochemical cell is submerged

A

Every thing but the wire/electrical contact

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11
Q

Which way do electrons flow and why

A

From anode to cathode
Cathode has higher electron affinity

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12
Q

What does current meassure

A

Charge

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13
Q

What does voltage measure

A

Electrical potential difference

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14
Q

(T/f) since there is a current, there is a voltage

A

T

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15
Q

Spontaneous def

A

The direction a reaction proceeds in naturally

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16
Q

What is required to proceed with an unspontaneous reaction

A

Induced charge

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17
Q

As electrons more from ___ to ___ through ___ , ions move from ___ to ___ through ___.

A

Anode
Cathode
Electrical contact
Anode
Cathode
Electrolyte

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18
Q

What is a half-cell reaction

A

A reaction which describes a element of intent in relation to a standard cell, allows us to compare elements of interest

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19
Q

How to tell anode vs cathode on an EMF table

A

More positive = cathode = wants electrons

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20
Q

What form is the EMF series in

A

Reduction form, typically based on a standard hydrogen electrode

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21
Q

What is a standard electrode

A

An electrode that is used as a reference to compare reactions or elements against

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22
Q

Describe SHE

A

Standard hydrogen electrode
Electrolyte of I mol/L [ ] of metal ions
298 k
Saturated with 1 atm of hydrogen gas
Platinum electrode
E not = 0.0 v

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23
Q

(T/f) liquid is compressible

A

F

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24
Q

Does potential change if conditions change from standard conditions? How do we account for this?

A

Yes, nerst’s eg

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25
Q

Examples of standard electrodes

A

Standard hydrogen electrode
Silver-silver chloride ( agci)
Calomel +0.244 V

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26
Q

Ag Cl standard electrode vs SHE

A

+ 0.222 V

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27
Q

What does the degree symbol mean?

A

Standard conditions

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28
Q

What are standard conditions?

A

298.15 K→ 25 C
I mol/ L cathode ions near cathode and same for anode
1 atm pressure

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29
Q

Voltage units

A

V= j/c

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30
Q

E meaning and relation to spontaneous

A

E = electrical potential
Positive = spontaneous

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31
Q

Delta g?

A

Gibs free energy, energy change in a system
>0 = cathode = absorbs energy
<0= anode = release energy

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32
Q

What is n

A

N = # of electrons transferred

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33
Q

F

A

Fairiday’s constant
Total energy change per mol of elections

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34
Q

What does the sign of delta G depend on

A

E

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35
Q

Corrosion def

A

Gradual deterioration of materials over time due to chemical or electrochemical reactions with surrounding environment leads to dissolution or formation of non-metallic scale or film
Results in deterioration of properties optical, physicals anything that effects function)
Occurs in metals and ceramics

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36
Q

Why is corrosion bad?

A

Leads to premature failure
Degradation of mechanical properties
Decrease of material integrity and thus structural strength
Costs money to fix things when they break

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37
Q

Ex of corrosion

A

Rust (iron)
Patina ( copper)
Oxidization
Chemical attacks
Anodizing

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38
Q

Can corrosion ever be stopped?

A

No, there will always be current, it can only be greatly slowed down

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39
Q

High level, how to slow down corrosion

A

Proper design, material selection and processing

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40
Q

Nickname for corrosion

A

Environmental attack

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41
Q

Degradation def

A

Corrosion in polymers due to internation with it’s environment

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42
Q

Requirements for corrosion (an electrochemical cell) to work

A

1) materials with different desire for elections (E not cell not equal to 0)
2) path for electron transfer
3) path for ion transfer

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43
Q

Concentration of solid species

A

Always 1 since they do not change

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44
Q

Can nearst eq be used for half-cell reactions

A

Yes be careful using it in reduction form

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45
Q

What are the two main ways corrosion can be categorized

A

By uniformity
By mechanism

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46
Q

Categories of uniformity of corrosion

A

Uniform corrosion → slow (slow ro corrosion), easy to spot (large area)
Localized corrosion → fast (fast ro corrosion), difficult to spot (small area)

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47
Q

Mechanisms of corrosion

A

Electro chemical cell
Galvanic Cell
Multiphase / impurity cell
Intergranular corrosion
Grain-grain boundary cell
* Stress-driven corrosion

Concentration cell
Crevice corrosion
Pitting corrosion
* microbial corrosion

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48
Q

What is galvanic corrosion

A

Two metals or alloys with different E in electrical contact with each other in a corrosive electrolyte
Is essentially an electrochemical cell

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49
Q

What is the most common electrolyte

A

Water

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50
Q

(T/f) dropping water on a part of a cell would not start concentration cell corrosion

A

F

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51
Q

Why does measure electrical potential between two electrodes sometimes not and up to the theoretical value

A

Water tends to be very active as an electrode and can react to beach an electrode, replacing ore of the existing electrodes

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52
Q

What ions can water be split into

A

H+ and OH-

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53
Q

What happens when water reacts instead of the intended electrodes

A

Instead of plating the other electrode, the anode its will react with H+ or OH- to create a gas

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54
Q

What determines which water ion interferes with a reaction

A

The presence of oxygen
Oxygen-free = H+
Aerated = OH-

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55
Q

What is the reaction quotient for half-cell reactions

A

1/ [ ion]

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56
Q

Are high ph substances corrosive? What about basic?

A

Ph = power of hydrogen = # of hydrogen ions
High ph = more hydrogen ions = more corrosive since more hydrogen electrode to react
Same premise for basic on an OH- scale

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57
Q

What is a multi-phasic or impurity cell

A

A electrochemical cell is created between different phases of an alloy
This creates an area of fast localized corrosion
Common in alloys since more alloys rely on multiplphases
Localized corrosion takes over and the alloy is no longer protected

*electrochemical potential difference created due phases with different potentials

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58
Q

What is sanitization

A

Multi-phasic cell corrosion in stainless steel
Usually occurs due to poor heat treatment
Anode = ferrite (2+) or austensite
Cathode = cemented (OH-)

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59
Q

What is grain-grain boundary cell corrosion

A
  • potential difference created by pot diff that exists between grains and GB
    It is very small but is enough to cause corrosion
    Ex: etching
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60
Q

In a grain-grain boundary cell, what are the electrodes

A

G.B = cathode
Grain = anode

61
Q

What is intergrainular corrosion

A

Preferential attack on GB due to potential difference created by multiphasic cells and grain-grain boundary cells
Applies to all metals

62
Q

(T/F) Intergranular Corrosion is the localized from of grain-grain boundary corrosion

A

F, opposite (at GB)

63
Q

What is a concentration cell

A

A cell created due to a difference in concentration of something which creates a E
occurs naturally
Often accompanied by stagnation

64
Q

What is a concentration cell

A

A cell which causes corrosion due to low or high concentrations of something
The driving force for the redox reaction is the concentration difference of an ion.
Occurs naturally

65
Q

(T/F) E diff determine corrosion rate

A

F

66
Q

What is crevice corrosion

A

Concentration cells created by the trapping of ions in small crevices
Crevices must be large enough for electrolyte to get in
Stagnation occurs

67
Q

What is stagnation

A

When it is difficult for ions to get out creating a rapid cycle of corrosion occur due to the little movement

68
Q

(T/F) Temperature difference can lead to diff in E

A

T

69
Q

(T/F) Stress changes E not

A

T

70
Q

What is pitting corrosion

A

A type of concentration cell corrosion
A extremely localized corrosion due to scratched and composition variations
Once started, it acts as crevice corrosion

71
Q

How do we know which chemical form (for example different charges) reacts as the electrode?

A

Compare the overall energy change of the systems
Higher E = more likley
Ensure comparison is made under same conditions

72
Q

What are e-ph diagrams

A

Plots the likley hood of each form of a element or compounds based on likley hood by ph and E
Basically a plot of Nernst eq for each reaction based on what’s more favourable for the overall reaction
Only favourable reactions are shown, less energetic forms don’t react and thus don’t show

73
Q

What is passivation

A

Formation of a protective jacket or film which limits corrosion

74
Q

Does passivation stop corrosion

A

No, it limits it by slowing it down
Corrosion current is not 0

75
Q

Does passivation always create a protective film

A

No, the film may be protective and stick to the surface it may be too small or too big and not protect it
If the film is too small, protection is not achieved
If the film is too big, the film flakes

76
Q

What is the Peanut butter ratio

A

Pilling Bedworth Ratio (P-BR)
Measure of the susceptibility of a metal to oxidization and corrosion
Compares vol change when a metal is oxidized and it’s normal volume
Determines how likley a metal is to form a protective film (passivation)

77
Q

How to interpret the PBR

A

PBR < 1 - porous oxide, corrosion may continue
1 <= PBR <= 2 - protective jacket
PBR > 2 0 chance of flaking or exploliate

78
Q

Steps to check for Passivation

A

1) Will it form a compound based on E- is it spontaneous?
2) check PBR

79
Q

Does the E change in a solution that is not water

A

Yes, substances may become more anodic or catholic depending on the solution used as an electrolyte
Likley hood of corrosion changes

80
Q

What is the relationship between PBR and E of a cell

A

Describes how the driving force of a raction

81
Q

What is the driving force

A

Describes if a reaction is favourable to go forwards
Does not describe how fast or how long it will take, just if the reaction will occur

82
Q

What is Thermodynamics

A

How likley a RX is to go forwards
Not time related
Measure by V
Basically the driving force

83
Q

What are the kinetic aspects of corrosion

A

The rate of reaction
How long and how fast

84
Q

What is the corrosion current

A

Number of atoms leaving the anode per time

85
Q

What is the current density and units

A

Current normalized per unit area
A/m2
C/S

86
Q

Assumptions made to calculate rate of corrosion

A

Assume flats surface with uniform distribution of electrons on surface- uniform corrosion

87
Q

What does CPR mean and assume

A

Change in thickness per time
Assumes unifrom corrosion over entire areas- same assumption as corrosion rate

88
Q

What is an acceptable corrosion limit

A

0.5 mm/yr

89
Q

CPR for very low corrosion

A

0.0254 mm/yr

90
Q

CPR for low corrosion

A

0.25 mm/yr

91
Q

CPR for fairly low corrosion

A

0.5

92
Q

CPR for high corrosion

A

1.27

93
Q

E units

A

V

94
Q

Delta G units

A

J

95
Q

F units

A

C/S

96
Q

M unit

A

G/mol

97
Q

P units (density)

A

G/vol

98
Q

Current density units

A

A/m^2

99
Q

Corrosion rate r unit

A

Mol/m^2s

100
Q

CPR units

A

Mm/yr

101
Q

What is stress driven corrosion

A

E is created due to residual stress
The stress changes local potential, creating a pot diff
Requires corrosion and stress to work
High stress area is anode
Low stress is cathode

102
Q

(T/F) Elastic and plastic strain change E

A

T

103
Q

What is microbial corrosion

A

Corrosion caused by excretions of bacteria as they form corrosive products
Products lead to concentration cells
Leads to localized corrosion by nucleating a pit

104
Q

What type of bacteria cause microbial corrosion

A

Iron-related bacteria
Acid-producing bacteria
Sulfate-reducing bacteria

105
Q

How to prevent corrosion

A

Remove the needed components:
E
Ion pathways
Pathways for e

106
Q

How can dissimilar electro-potential be prevented

A

Proper material selection- minimizes basic galvanize cells
Proper heat treatment - minimized stress driven cells and multi-phasic cells
Proper design and manufacturing - minimizes geometries with crevices
Remove electrical contract by insulating diff materials

Use a smaller area of exposed dissimilar materials - slows down CPR
Avoid rivets - prone to crevice corrosion - same material tho
Avoid solder or braze - prone to galvanic cells as they are diff material from original - may cause stress driven corrosion

107
Q

Why does a lemon battery stop working

A

When lemon juice is used up, no more H plus supply so no more [] diff and thus no more E diff

108
Q

Welding vs Rivet vs Brase/Solder

A

Welding is the best if done properly

Avoid rivets - prone to crevice corrosion - same material tho
Avoid solder or braze - prone to galvanic cells as they are diff material from original - may cause stress driven corrosion

109
Q

How can electrolyte contact be limited

A

Anodizing
Coatings : tight sealing paint, oil, grease
Use inhibitors : WD:40
Prevent water pooling
Seal up gaps and crevices

110
Q

What is anodizing

A

forcibly increase thickness of passive film by using power supply to force higher rate

111
Q

What is Glavanization

A

A process which can be done to steel
Slows down the rate of corrosion
Sacrificial anode but for steel
When in a corrosive environment, Zn is forced to be the sacrificial anode and steel becomes the cathode
Zn reacts again to for ZnO and protect again

112
Q

Requirement for anodizing

A

Metal with a PBR of between 1 and 2 must be passivated

113
Q

What is sacrificial anode protection

A

A metal is coated onto another metal with the idea that in a corrosive environment, the coating will become a sacrificial anode to act as a layer of protection for the cathode
The anode reacts, the ions get taken by the air and thus the coating weakens until its gone

114
Q

What is a requirement for galvanization and sacrificial anode for it to work well

A

Large anode to cathode ratio
Slows down the RX further

115
Q

What is catholic protection

A

Involves either using a sacrificial node or an applied potential (inert cathode)

116
Q

Passive vs active catholic protection

A

Passive = natural - sacrificial anode
Active = need constant applied power supply to drive current - applied potential

117
Q

What is inert cathode

A

Also called applied potential
Active form of catholic protection
Ex : electronic rust inhibitor module for cars
Essential undoing the reactions which produce rust or other forms of corrosion

118
Q

What is swelling

A

Absorption of liquid (solvent) or a solute (polymer)

119
Q

How does swelling effect polymers

A

Makes it softer, more ductile
Lowers Tg
Grows in size
chain does not break chains

120
Q

How does chain length effect properties of molecules

A

Increase chain length = increase elastic modulus and yield strength

121
Q

How does swelling effect the properties of a polymer

A

No change, since chains aren’t broken, no change in properties other than volume

122
Q

What is dissolution

A

Occurs after swelling
Chains are disentangled
May break chains
Thus may lower elastic modulus and yield strength

123
Q

When is swelling and dissolution likley to happen to polymers

A

When the solvent and polymer have high similarity in chemical simularity

124
Q

What is scission

A

Severance of molecular chain bonds
Can be due to
Radiation (x-ray, gamma, UV) - ionization of bonding e - ionizing energy is the energy that can break up chains
Chemical reaction
Thermal effect- due to elevated temperature- when this occurs depends on the melting temp of the polymer

125
Q

What is weathering

A

Degradation of polymers in outdoor conditions
Ex: oxidation, UV radiation, moisture

126
Q

What are the steps to degreation

A

Swelling, dissolution, scission

127
Q

Why do we want materials to be durable but not too durable

A

We want it to be strong and last but we need to be able to dispose of it at the end of its life cycle

128
Q

What is embodied energy

A

Energy needed to create 1 kg of stock material

129
Q

What is LCA

A

Life cycle analysis
Accesses the environmental impact throughout the life cycle of the product

130
Q

What LCI

A

Life cycle inventory
A list of natural material used and their emissions

131
Q

What is the material life cycle

A

In a endless circle

Product manufactured — product used — end of life —- material produced
Natural products can be added to the material production stage

Raw material refining - manufacturing - transport - use- end of life (disposal, recycling)

132
Q

What counts as emissions in a material life cycle LCI

A

Co2
NO2
SOX
Particulates
Toxic waste
Low grade heat

133
Q

Biodegradable

A

Once in the landfill, material can quickly return to the earth in its original state through interaction with its environment in a mearurable amount of time

134
Q

Recyclable

A

Materials that can be reprocessed at the end of life and returned to the life cycle as in a different product

135
Q

What are the types of recycling

A

Open loop recylcing
Close loop recylcing
Co-firing

136
Q

What is open loop recycling

A

Recycled product re-enters back into the same system

137
Q

What is close loop recycling

A

Recycled product re-enters into a pool and distributed across multiple systems

138
Q

What is co-firing

A

Incineration to produce energy for other uses
Only some (very little) of the embodied energy is recuperated

139
Q

Re-cycling processes from more environmentally friendly to least

A

Closed loop
Open loop
Co-firing

140
Q

(T/F) Most metals are not biodegradable

A

F
Most are biodegradable since it can be corroded by various chemicals found in nature 0 thought this takes a long time and may create things that are toxic for wildlife

141
Q

(T/F) Metals are recyclable

A

T
RE-melting and hence re-casting and or reforming metal into new parts or products is an option but still needs energy

142
Q

Why is recycling of metals still a concern for sustainablity

A

Needs energy

143
Q

(T/F) With recycling, all energy is recovered

A

F
Only a portion of embodied energy can be recovered

144
Q

Why is recycling metals possibly not advantageous

A

Metals and alloys have a very specific composition
Anything less or extra is an impurity which may effect the properties of the metal and thus make it considered poor quality
Makes recycling difficult

145
Q

What is idle at

A

An app that creates a simplified LCA
Describes eco cost of producing a product
Shows us how environmentally unfriendly something is

146
Q

What is eco-cost

A

Money needed to prevent the environmental burden of producing a product, material or process

147
Q

Why is light weighting beneficial and disadvantagoues

A

Using lighter (Less dense) materials requires less energy to transport and use
But may be lower is strength/ toughness so it may require strengthening

148
Q

T/F galvanic corrosion is a type of electrochemical cell

A

T

ME 230: Control Of Properties Of Materials (7 decks)

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