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CP-2 > Chapter - 1 (Corrosion Cell) > Flashcards

Chapter - 1 (Corrosion Cell) Flashcards

1
Q

Corrosion is ,,,,,,,,,process

A

an electrochemical

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2
Q

Corrosion is an electrochemical process involving the ,,,,,,,

A

Flow of electrons and ions

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3
Q

No metal loss occure at……

A

cathode

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4
Q

Electrochemical corrosion involves the transfer of

electrons across ,,,,,,

A

metal/electrolyte interfaces

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5
Q

Corrosion occurs within a ,,,,,,, that consists of four parts

A

corrosion cell

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6
Q

A corrosion cell consists of four parts,,,,

A

Anode
Cathode
Electrolyte
Electronic/Metallic Path

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7
Q

the metal ions combine with hydroxyl ions in the electrolyte to form ,,,,,,,

A

Metal hydroxide, or rust

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8
Q

Oxidation (corrosion) of the metal occurs at the ,,,,,,,

A

Anodic surfaces

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9
Q

Reduction of hydrogen ions occurs at the ,,,,,,

A

Cathodes

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10
Q

The term ―”oxidation” is not necessarily associated with ,,,,

A

Oxygen

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11
Q

The measure of the electrochemical difference between two electrodes in an electrolyte

A

Voltage

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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

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13
Q

At the cathodic surface, the electrons from the ,,,,,meet ,,,,,, ions from the solution

A

anode

hydrogen

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14
Q

Oxidation (corrosion) of the metal occurs at the,,,,,,,,,

surfaces and reduction of ,,,,, ions occurs at the ,,,,,,,

A

Anodic
Hydrogen
Cathodes

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15
Q

True or false

Is oxidation necessarily associated with oxygen ?

A

false

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16
Q

,,,,,,,, is the measure of the electrochemical difference between two electrodes in an electrolyte

A

Voltage

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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

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18
Q

1 coulomb of electricity will do ,,,,, of work in going from one point to another

A

1 joule

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19
Q

The electrode potential is measured against a ,,,,,,

A

standard reference cell.

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20
Q

Metals occur in nature in the form of various chemical compounds referred to as,,,,,,

A

Ores

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21
Q

The amount of energy required by a metal during the refining process determines the ,,,,,, or ,,,, of the metal

A

voltage

active state

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22
Q

The voltage is relatively ,,,,,, for such metals as magnesium, aluminum, and iron,

A

High

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23
Q

The voltage is relatively ,,,,,,,,,,,for such metals as copper and silver

A

Low

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24
Q

The higher the energy, the more ,,,,,,, the metal and the more tendency it has to ,,,,,,,,

A

active

corrode

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25
Q

The most common iron ore, ,,,,,,,,,, is an oxide of iron (Fe2O3).

A

hematite

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26
Q

The most common product of the corrosion of iron,,,,,,,,

has the same chemical composition

A

Rust

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27
Q

The energy required to convert iron ore to

metallic iron is ,,,,,,, when the iron corrodes to form the oxide

A

“returned”

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28
Q

Iron always is found in an ,,,,,,, state

A

oxidized

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29
Q

Iron is considered thermodynamically,,,,,

A

unstable

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30
Q

True or false

Gold is more noble than zinc?

A

True

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31
Q

The potential between the two electrodes, also called the ,,,,,,,

A

electromotive force (emf)

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32
Q

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 ,,,,,,,,

A

equal
anode
cathode

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33
Q

This ,,,,,,,or ,,,, between the two electrodes is the driving force for electrochemical corrosion.

A

emf

voltage

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34
Q

If a metallic path connects the two electrodes, the voltage difference will cause a ,,,,,, to flow between them

A

current

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35
Q

In relation to a corrosion cell,,,,,, is the net transfer of electric charge per unit time

A

Current

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36
Q

When electrically interconnecting two different metals in a common electrolyte, the more active metal will tend to become the ,,,,, of the corrosion cell

A

anode

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37
Q

A more useful method of ordering metals is the ,,,,,,

A

galvanic series

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38
Q

A galvanic series is based on the behavior of a metal in a particular ,,,,,, and the most common electrolyte used is ,,,,,,,,,,

A

electrolyte

seawater

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39
Q

The ,,,,,,, expresses the exact electromotive force of a cell in terms of the activities of products and reactants of the cell

A

Nernst Equation

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40
Q

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.

A

25

hydrogen

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41
Q

The higher the concentration of metal ions, the ,,,,,

(or more noble) the metal

A

less active

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42
Q

In reference to the temperature in a corrosion cell, the electrode at the higher temperature becomes the ,,,,,

A

anode

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43
Q

This is a natural phenomenon— temperature increases with ,,,,,,

A

depth

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44
Q

Highly stressed areas of a metal will tend to be at ,,,,,,energy levels, thus ,,,, active than less stressed areas

A

higher

more

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45
Q

True or False (t or f):

Corrosion cells may form because of differences in the electrolyte

A

True

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46
Q

,,,,,,, cells are responsible for much of the corrosion that takes place in soils, particularly in bare or poorly coated pipe

A

Concentration

47
Q

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 ___.

A

conductive, anode

conductive, cathode

48
Q

The two most common types of concentration cells involved in promoting corrosion are ____ and ____.

A

oxygen,

metal ion

49
Q

What is the most common of the cathodic depolarizers, that can maintain and promote a cathodic reaction?

A

oxygen

50
Q

Most corrosion on pipelines is on the ____ portion of the pipe

A

Bottom

51
Q

If a pipe is running through a section of pavement and through a section of non pavement:

A

anode is the metal under the pavement, the cathode is the metal outside the pavement

52
Q

In a metal ion concentration cell, the surface in contact with ____ concentration of metal ions acts as the ____

A

lower, anode

53
Q

Theoretically, the potential of a structure changes by about ,,,,,,, mV for each pH unit

A

60

54
Q

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?

A

-560mV

55
Q

True or false (t or f)

an acidic pH can be harmful to concrete, such as reinforced concrete structures?

A

True

56
Q

A pH of less than ____ is considered to be harmful to concrete?

A

5

57
Q

The rate of corrosion is directly ____ to ____ flow?

A

proportional, current

58
Q

Faraday’s Law relates weight loss of metal in a corrosion cell with ,,,,,,, and,,,,,,,,

A

time, current flow

59
Q

Faraday’s Law is given by the following equation:

A

W = K I t

60
Q

All things being equal, the greater the magnitude of the difference between two voltages of metals, the ____ the current flow and rate of corrosion

A

higher

61
Q

True or False ( t or f)

Magnesium will corrode at a slower rate when connected to steel rather than zinc?

A

False

62
Q

Reference electrodes, or half-cells, are important devices that permit measuring the ,,,,,,, of a metal surface exposed to an electrolyte

A

potential

63
Q

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?

A

SHE

64
Q

A structure-to-electrolyte potential is actually the potential difference between the structure and a ,,,,,,

A

reference electrode

65
Q

Most common used reference electrode for measuring potentials of underground structures?

A

CSE

66
Q

It is not suitable for use in a chloride electrolyte as the chloride ions will migrate through the porous plug and contaminate the ,,,,,,

A

CSE

67
Q

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

A

–20 mV

–95 mV

68
Q

Clean or replace field electrodes if they are more than ,,,,, mV different from your calibrating electrode

A

5 mV

69
Q

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

A
  1. 5 mV

0. 9 mV

70
Q

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?

A

True

71
Q

Silver-silver chloride (Ag-AgCl) reference electrodes are used for measurements in ,,,,,, and also used in

A

seawater,

concrete structures

72
Q

Which of the following is primarily a laboratory electrode

A

Calomel Reference Electrode (CRE)

73
Q

The saturated calomel reference electrode consists of ,,,,,

A

mercury-mercurous chloride in a saturated potassium chloride solution

74
Q

When doing a structure to electrolyte potential , the structure is connected via the _____ terminal and the reference is connected via the _____ terminal

A

positive, negative

75
Q

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.

A

True

76
Q

Depolarizers include:

A

dissolved oxygen
microbiological activity
water flow

77
Q

Polarization ,,,,, the potential difference between the

anode and ,,,, areas

A

lowers, cathode

78
Q

Polarization always occurs in the direction to ,,,,,

A

oppose the current flow causing it

79
Q

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

A

reduces, steady

80
Q

The difference between the polarized potentials of the anode and cathode is the ,,,,,, of the
corrosion cell

A

driving voltage

81
Q

The current at this steady state condition is defined as the ,,,,, of the system

A

corrosion current (ICORR)

82
Q

Evans diagrams are used for

A

graphically illustration concept of polarization

83
Q

In general, polarization is related to the depletion of the ,,,,,,,, and the buildup of ,,,,,,,, products.

A

reactants, reaction

84
Q

Anything that favors the buildup of reaction products or the depletion of reactants ,,,,,,,

A

increases polarization

85
Q

There are two types of polarization—

A

activation and concentration

86
Q

Activation polarization is the result of the r,,,,,,, including the actual transfer of charge

A

eaction steps at the structure/electrolyte interface

87
Q

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 ,,,,,,

A

activation polarization.

88
Q

Concentration polarization is the result of reaction steps involving the diffusion of reactants up to or the reaction products,,,,,,,

A

away from the reaction surface (structure interface)

89
Q

If the slowest step in the overall process involves waiting for arrival of reactants or the removal of reaction products, the reaction is under ,,,,,,

A

concentration polarization control

90
Q

The ability of the reactants to reach the reacting surface and the reaction products to move away from the reacting surface determines the ,,,,,,

A

limiting current density

91
Q

The total polarization of a structure is the sum of the ,,,,,

A

activation and concentration polarization

92
Q

Polarization measurements include a ,,,,,,,,component that is produced by current, I, through electrolyte to the electrode.

A

voltage (―IR Drop‖)

93
Q

This IR component is not ,,,,,, and must be taken into consideration or eliminated from measurements when the potential is used to meet a criterion

A

polarization

94
Q

Since polarization is caused by ,,,,,, then as current increases, polarization will ,,,,,,

A

current, increases

95
Q

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

A

increase, decrease

96
Q

An increase in ions will result in a ,,,,,, in resistivity

A

decrease

97
Q

Polarization is a function of the ,,,,,,

A

current density or current per unit area.

98
Q

a coated structure will polarize ,,,,,,,, than a bare structure with a given amount of current.

A

more rapidly

99
Q

A small anode and large cathode is undesirable because the pitting is greater compared to a large ,,,, and small ,,,,

A

anode, cathode

100
Q

an increase in temperature has a tendency to speed up chemical reactions, which ,,,,,, the electrodes and increases current

A

depolarizes

101
Q

Likewise, a decrease in temperature results in an increase in,,,,,,

A

polarization.

102
Q

An increase in the metal ion concentration of the anode metal results in ,,,, in polarization of the anode and a decrease in ,,,

A

an increase, current.

103
Q

Polarization of the cathode can be affected by the concentration of cathodic reactants, ,,,,,,

A

such as oxygen or hydrogen ions

104
Q

An increase in the concentration of either of these reactants will decrease ,,,, of the cathode and increase ,,,

A

polarization,,,,current and vice versa

105
Q

Passivity can be defined as the ,,,

A

loss of chemical reactivity

106
Q

Selective Leaching is ….

A

the selective removal of one of the elements from an alloy

107
Q

The prevention of hydrogen embitterment depends on keeping the potential below the hydrogen evolution potential, which depends on the ,,,,,,

A

pH.

108
Q

In general, hydrogen is generated in neutral environments at ,,,,

A

– 1,044 mVCSE

109
Q

The lower the pH, the ,,,, the hydrogen evolution

potential

A

lower

110
Q

For aluminum, the polarized potential must be kept below ,,,,,,,to avoid alkali corrosion.

A

– 1,200 mVCSE

111
Q

For titanium, the maximum potential is ,,,,, to prevent hydriding

A

–700 mV

112
Q

For prestressed concrete, polarized potentials more negative than ,,,,, should be avoided

A

–1,000 mVssc

113
Q

SCC of high-strength pipeline steels cracking occurs in a narrow potential range ,,,, at a pH between

A

(–525 to –725 mVCSE),,,,8 and 10.5

114
Q

The SCC cracking occurs because of the formation of ,,,,s and ,,,, at the steel surface

A

carbonate, bicarbonates

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