Chapter - 1 (Corrosion Cell) Flashcards
(114 cards)
1
Q
Corrosion is ,,,,,,,,,process
A
an electrochemical
2
Q
Corrosion is an electrochemical process involving the ,,,,,,,
A
Flow of electrons and ions
3
Q
No metal loss occure at……
A
cathode
4
Q
Electrochemical corrosion involves the transfer of
electrons across ,,,,,,
A
metal/electrolyte interfaces
5
Q
Corrosion occurs within a ,,,,,,, that consists of four parts
A
corrosion cell
6
Q
A corrosion cell consists of four parts,,,,
A
Anode
Cathode
Electrolyte
Electronic/Metallic Path
7
Q
the metal ions combine with hydroxyl ions in the electrolyte to form ,,,,,,,
A
Metal hydroxide, or rust
8
Q
Oxidation (corrosion) of the metal occurs at the ,,,,,,,
A
Anodic surfaces
9
Q
Reduction of hydrogen ions occurs at the ,,,,,,
A
Cathodes
10
Q
The term ―”oxidation” is not necessarily associated with ,,,,
A
Oxygen
11
Q
The measure of the electrochemical difference between two electrodes in an electrolyte
A
Voltage
12
Q
The electrons generated at the anode pass through the ,,,,,, to the surface of the ,,, areas immersed in the electrolyte.
A
electronic path
cathodic
13
Q
At the cathodic surface, the electrons from the ,,,,,meet ,,,,,, ions from the solution
A
anode
hydrogen
14
Q
Oxidation (corrosion) of the metal occurs at the,,,,,,,,,
surfaces and reduction of ,,,,, ions occurs at the ,,,,,,,
A
Anodic
Hydrogen
Cathodes
15
Q
True or false
Is oxidation necessarily associated with oxygen ?
A
false
16
Q
,,,,,,,, is the measure of the electrochemical difference between two electrodes in an electrolyte
A
Voltage
17
Q
The ,,,,,,, represents the reversible work to move a unit charge from the electrode surface
through the solution to the reference electrode.
A
Electrode potential
18
Q
1 coulomb of electricity will do ,,,,, of work in going from one point to another
A
1 joule
19
Q
The electrode potential is measured against a ,,,,,,
A
standard reference cell.
20
Q
Metals occur in nature in the form of various chemical compounds referred to as,,,,,,
A
Ores
21
Q
The amount of energy required by a metal during the refining process determines the ,,,,,, or ,,,, of the metal
A
voltage
active state
22
Q
The voltage is relatively ,,,,,, for such metals as magnesium, aluminum, and iron,
A
High
23
Q
The voltage is relatively ,,,,,,,,,,,for such metals as copper and silver
A
Low
24
Q
The higher the energy, the more ,,,,,,, the metal and the more tendency it has to ,,,,,,,,
A
active
corrode
25
The most common iron ore, ,,,,,,,,,, is an oxide of iron (Fe2O3).
hematite
26
The most common product of the corrosion of iron,,,,,,,,
| has the same chemical composition
Rust
27
The energy required to convert iron ore to
| metallic iron is ,,,,,,, when the iron corrodes to form the oxide
"returned"
28
Iron always is found in an ,,,,,,, state
oxidized
29
Iron is considered thermodynamically,,,,,
unstable
30
True or false
| Gold is more noble than zinc?
True
31
The potential between the two electrodes, also called the ,,,,,,,
electromotive force (emf)
32
The potential between the two electrodes, also called the electromotive force (emf), is ,,,,,,, in sign and magnitude to the electrode potential of the ,,,,, less the electrode potential of the ,,,,,,,,
equal
anode
cathode
33
This ,,,,,,,or ,,,, between the two electrodes is the driving force for electrochemical corrosion.
emf
| voltage
34
If a metallic path connects the two electrodes, the voltage difference will cause a ,,,,,, to flow between them
current
35
In relation to a corrosion cell,,,,,, is the net transfer of electric charge per unit time
Current
36
When electrically interconnecting two different metals in a common electrolyte, the more active metal will tend to become the ,,,,, of the corrosion cell
anode
37
A more useful method of ordering metals is the ,,,,,,
galvanic series
38
A galvanic series is based on the behavior of a metal in a particular ,,,,,, and the most common electrolyte used is ,,,,,,,,,,
electrolyte
| seawater
39
The ,,,,,,, expresses the exact electromotive force of a cell in terms of the activities of products and reactants of the cell
Nernst Equation
40
Standard conditions for pure metals in the
emf series are based on one unit activity of metal ions in the electrolyte at ,,,,,,oC with no impurities in the metal or electrolyte and with reference to a standard
,,,,,, electrode.
25
| hydrogen
41
The higher the concentration of metal ions, the ,,,,,
| (or more noble) the metal
less active
42
In reference to the temperature in a corrosion cell, the electrode at the higher temperature becomes the ,,,,,
anode
43
This is a natural phenomenon— temperature increases with ,,,,,,
depth
44
Highly stressed areas of a metal will tend to be at ,,,,,,energy levels, thus ,,,, active than less stressed areas
higher
| more
45
True or False (t or f):
Corrosion cells may form because of differences in the electrolyte
True
46
,,,,,,, cells are responsible for much of the corrosion that takes place in soils, particularly in bare or poorly coated pipe
Concentration
47
In many cases in naturally occurring soils, a portion of pipe lying in the more _____ soil is the ____ and in the less ____soil is the ___.
conductive, anode
| conductive, cathode
48
The two most common types of concentration cells involved in promoting corrosion are ____ and ____.
oxygen,
| metal ion
49
What is the most common of the cathodic depolarizers, that can maintain and promote a cathodic reaction?
oxygen
50
Most corrosion on pipelines is on the ____ portion of the pipe
Bottom
51
If a pipe is running through a section of pavement and through a section of non pavement:
anode is the metal under the pavement, the cathode is the metal outside the pavement
52
In a metal ion concentration cell, the surface in contact with ____ concentration of metal ions acts as the ____
lower, anode
53
Theoretically, the potential of a structure changes by about ,,,,,,, mV for each pH unit
60
54
The corrosion potential of a metal might be -500mV in an environment with a pH of 7, but the corrosion potential might be ____ at a pH of 8?
-560mV
55
True or false (t or f)
an acidic pH can be harmful to concrete, such as reinforced concrete structures?
True
56
A pH of less than ____ is considered to be harmful to concrete?
5
57
The rate of corrosion is directly ____ to ____ flow?
proportional, current
58
Faraday's Law relates weight loss of metal in a corrosion cell with ,,,,,,, and,,,,,,,,
time, current flow
59
Faraday’s Law is given by the following equation:
W = K I t
60
All things being equal, the greater the magnitude of the difference between two voltages of metals, the ____ the current flow and rate of corrosion
higher
61
True or False ( t or f)
Magnesium will corrode at a slower rate when connected to steel rather than zinc?
False
62
Reference electrodes, or half-cells, are important devices that permit measuring the ,,,,,,, of a metal surface exposed to an electrolyte
potential
63
Which reference electrode is considered a primary reference electrode because it is used to determine the potential of other secondary reference electrodes that are better suited for field use?
SHE
64
A structure-to-electrolyte potential is actually the potential difference between the structure and a ,,,,,,
reference electrode
65
Most common used reference electrode for measuring potentials of underground structures?
CSE
66
It is not suitable for use in a chloride electrolyte as the chloride ions will migrate through the porous plug and contaminate the ,,,,,,
CSE
67
Chloride contamination changes the chemical reactions and the reference potential becomes a lower composite with the error being ,,,,,,,mV at concentrations of 5 ppt and ,,,,,,, mV at concentrations of 10 ppt
–20 mV
| –95 mV
68
Clean or replace field electrodes if they are more than ,,,,, mV different from your calibrating electrode
5 mV
69
A temperature correction of ,,,,,,, mV/ F or ,,,,, mV/ C must be either added or subtracted when reference temperature is above or below ambient temperature, respectively
0. 5 mV
| 0. 9 mV
70
True or false (t or f)
The potential of a reference electrode in the sun can decrease from 10 to 50mV versus an electrode kept in the dark?
True
71
Silver-silver chloride (Ag-AgCl) reference electrodes are used for measurements in ,,,,,, and also used in
seawater,
| concrete structures
72
Which of the following is primarily a laboratory electrode
Calomel Reference Electrode (CRE)
73
The saturated calomel reference electrode consists of ,,,,,
mercury-mercurous chloride in a saturated potassium chloride solution
74
When doing a structure to electrolyte potential , the structure is connected via the _____ terminal and the reference is connected via the _____ terminal
positive, negative
75
True or False (t or f)
The potential of a STATIONARY reference electrode should be checked from time to time
with a portable reference electrode that is known to be accurate under "no
current" conditions.
True
76
Depolarizers include:
dissolved oxygen
microbiological activity
water flow
77
Polarization ,,,,, the potential difference between the
| anode and ,,,, areas
lowers, cathode
78
Polarization always occurs in the direction to ,,,,,
oppose the current flow causing it
79
As the resistance of the electronic and/or electrolytic paths reduces, the voltage difference between the polarized electrodes also ,,,,,,, and both electrodes
come to a ,,,,, state polarized potential
reduces, steady
80
The difference between the polarized potentials of the anode and cathode is the ,,,,,, of the
corrosion cell
driving voltage
81
The current at this steady state condition is defined as the ,,,,, of the system
corrosion current (ICORR)
82
Evans diagrams are used for
graphically illustration concept of polarization
83
In general, polarization is related to the depletion of the ,,,,,,,, and the buildup of ,,,,,,,, products.
reactants, reaction
84
Anything that favors the buildup of reaction products or the depletion of reactants ,,,,,,,
increases polarization
85
There are two types of polarization—
activation and concentration
86
Activation polarization is the result of the r,,,,,,, including the actual transfer of charge
eaction steps at the structure/electrolyte interface
87
If the charge transfer reaction or any reaction step on the metal surface is the slowest step in the overall reaction process, the process is under ,,,,,,
activation polarization.
88
Concentration polarization is the result of reaction steps involving the diffusion of reactants up to or the reaction products,,,,,,,
away from the reaction surface (structure interface)
89
If the slowest step in the overall process involves waiting for arrival of reactants or the removal of reaction products, the reaction is under ,,,,,,
concentration polarization control
90
The ability of the reactants to reach the reacting surface and the reaction products to move away from the reacting surface determines the ,,,,,,
limiting current density
91
The total polarization of a structure is the sum of the ,,,,,
activation and concentration polarization
92
Polarization measurements include a ,,,,,,,,component that is produced by current, I, through electrolyte to the electrode.
voltage (―IR Drop‖)
93
This IR component is not ,,,,,, and must be taken into consideration or eliminated from measurements when the potential is used to meet a criterion
polarization
94
Since polarization is caused by ,,,,,, then as current increases, polarization will ,,,,,,
current, increases
95
where the controlling factor is current, an increase in current causes an ,,,,,,, in polarization, but where the controlling factor is polarization, an increase in polarization will cause a ,,,,, in current
increase, decrease
96
An increase in ions will result in a ,,,,,, in resistivity
decrease
97
Polarization is a function of the ,,,,,,
current density or current per unit area.
98
a coated structure will polarize ,,,,,,,, than a bare structure with a given amount of current.
more rapidly
99
A small anode and large cathode is undesirable because the pitting is greater compared to a large ,,,, and small ,,,,
anode, cathode
100
an increase in temperature has a tendency to speed up chemical reactions, which ,,,,,, the electrodes and increases current
depolarizes
101
Likewise, a decrease in temperature results in an increase in,,,,,,
polarization.
102
An increase in the metal ion concentration of the anode metal results in ,,,, in polarization of the anode and a decrease in ,,,
an increase, current.
103
Polarization of the cathode can be affected by the concentration of cathodic reactants, ,,,,,,
such as oxygen or hydrogen ions
104
An increase in the concentration of either of these reactants will decrease ,,,, of the cathode and increase ,,,
polarization,,,,current and vice versa
105
Passivity can be defined as the ,,,
loss of chemical reactivity
106
Selective Leaching is ....
the selective removal of one of the elements from an alloy
107
The prevention of hydrogen embitterment depends on keeping the potential below the hydrogen evolution potential, which depends on the ,,,,,,
pH.
108
In general, hydrogen is generated in neutral environments at ,,,,
– 1,044 mVCSE
109
The lower the pH, the ,,,, the hydrogen evolution
| potential
lower
110
For aluminum, the polarized potential must be kept below ,,,,,,,to avoid alkali corrosion.
– 1,200 mVCSE
111
For titanium, the maximum potential is ,,,,, to prevent hydriding
–700 mV
112
For prestressed concrete, polarized potentials more negative than ,,,,, should be avoided
–1,000 mVssc
113
SCC of high-strength pipeline steels cracking occurs in a narrow potential range ,,,, at a pH between
(–525 to –725 mVCSE),,,,8 and 10.5
114
The SCC cracking occurs because of the formation of ,,,,s and ,,,, at the steel surface
carbonate, bicarbonates
