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MATERIAL SCIENCE and ENGINEERING > Chapter 8: Corrosion and Degradation of Materials > Flashcards

Chapter 8: Corrosion and Degradation of Materials Flashcards

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1
Q

there is actual
material loss either by
dissolution (corrosion) or by
the formation of nonmetallic
scale or film (oxidation).

A

metals

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2
Q

are relatively resistant to deterioration, which
usually occurs at elevated temperatures or in rather extreme
environments

A

Ceramic materials

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3
Q

For polymers, mechanisms and consequences differ from those for
metals and ceramics, and the term ___ is most frequently
used

A

degradation

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4
Q

Polymers may dissolve when exposed to a liquid solvent, or they may
absorb the solvent and swell; also, ___
(primarily ultraviolet) and heat may cause alterations in their
molecular structures

A

electromagnetic radiation

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5
Q

*___ of an object occurs as a result of the interaction between the environment or with the materials that form the object

*several ways in which ceramics break down physically and chemically

A

degradation

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6
Q

it is in the nature of all the materials used for construction to eventually ___ and ___

A

degrade and deteriorate

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7
Q

the destructive electrochemical attack of a material

A

corrosion

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8
Q

why metals corrodes?

A

redox reaction (reduction-oxidation)

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9
Q

two reactions necessary in corrosion of zinc in acid

A

oxidation reaction and reduction reaction

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10
Q

occurs when the iron in the metal oxidises

A

steel rusting

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11
Q

solution for steel rusting

A

alloying with chromium (stainless steel)
painting/coating the metal

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12
Q

generated by
coupling to the standard
hydrogen electrode, standard
half-cells for various metals
and ranking them according
to measured voltage

A

electromotive force (emf)

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13
Q

the rate of
material removal as a consequence of
the chemical action, is an important
corrosion parameter

A

corrosion penetration rate (CPR)

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14
Q

The variables in the corrosion environment, which include ___ can have a decided
influence on the corrosion properties of the materials that are in
contact with it.

A

fluid velocity, temperature, and composition

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15
Q

In most instances, increasing fluid velocity enhances the rate of
corrosion due to

A

erosive effects

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16
Q

Increasing the concentration of the corrosive species (e.g., H+
ions in acids) in many situations produces a more rapid rate of

A

corrosion

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17
Q

forms of corrosion

A

stress corrosion
erosion-corrosion
pitting
crevice
galvanic
intergranular
selective leaching
uniform attack

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18
Q

work together at crack tips

A

stress corrosion

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19
Q

break down of passivating layer by erosion (pipe elbows)

A

erosion-corrosion

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20
Q

downward propagation of small pits & holes

A

pitting

21
Q

between two pieces of the same metal

A

crevice

22
Q

Dissimilar metals are physically joined. The more anodic one corrodes

A

galvanic

23
Q

corrosion along grain boundaries, often where special phases exist

A

intergranular

24
Q

preferred corrosion of one element/constituent

A

selective leaching

25
Q

oxidation & reduction occur uniformly over surface

also known as general attack corrosion

most common type of corrosion and is caused by a chemical or electrochemical reaction

greater amount of corrosion destruction but safe form of corrosion

predictable, manageable and preventable

A

uniform attack

26
Q

it specifically attacks one area of the metal structure

A

localized corrosion

27
Q

classification of localized corrosion

A

pitting corrosion
crevice corrosion
filiform corrosion

28
Q

results when a small hole, or cavity, forms in the metal, usually as a result of de-passivation of a small area

produces localized galvanic reaction

often difficult to detect due to the fact that it is relatively small

A

pitting corrosion

29
Q

similar to pitting

it occurs at a specific location

often associated with stagnant micro-environment

A

crevice corrosion

30
Q

occuring under painted or plated surfaces when water breaches the coating

begins with small defects in the coating and spreads to cause structural weakness

A

filiform corrosion

31
Q

occurs when two different metals are located together in a corrosive electrolyte

forms between two metals, where one becomes anode and one becomes cathode

A

galvanic corrosion

32
Q

three conditions must exists for galvanic corrosion to occur

A

-electrochemically dissimilar metals must be present
-the metals must be in electrical contact
-the metals must be exposed to an electrolyte

33
Q

is a corrosion process that can result from a combination of environmental conditions affecting the metal

A

environmental cracking

34
Q

types of environmental cracking

A

-stress corrosion cracking (SCC)
-corrosion fatigue
-hydrogen-induced cracking
-liquid metal embrittlement

35
Q

___ or flow-accelerated corrosion, results when a protective layer of oxide on a metal surface is dissolved or removed by wind or water, exposing the underlying metal to further corrode and deteriorate

A

flow-assisted corrosion (FAC)

36
Q

-occurs as a result of repeated wearing, weight and/or vibration on an uneven, rough surface

-often found in rotation and impact machinery

A

fretting corrosion

36
Q

-is a chemical or electrochemical atttack on the grain boundaries of a metal

-often occurs due to impurities in the metal which tend to be present in higher contents near grain boundaries and these boundaries can be more vulnerable to corrosion than the bulk of the metal

A

transgranular and intergranular corrosion

36
Q

de-alloying also called

A

selective leaching

36
Q

can also be caused by high temperature oxidization, sulfidation and carbonization

A

high temperature corrosion

37
Q

-is the selective corrosion of a specific element in an alloy

-the most common type of it is de-zincification of unstabilized brass

-the result of corrosion in such cases is a deteriorated and porous copper

A

de-alloying

38
Q

corrosion prevention

A

-through the judicious selection of materials
-cost may be a significant factor
-changing the character of the environment
-lowering the fluid temperature and/or velocity
-increasing or decreasing the concentration of some species

39
Q

are substances or mixtures that in low concentration and in aggressive environment inhibit, prevent or minimize the corrosion

A

inhibitors

39
Q

3 mechanism of the inhibitor

A

-inhibitor is chemically adsorbed on the surface of the metal
-inhibitor leads a formation of a film by oxide protection of the base metal
-inhibitor reacts with a potential corrosive component

40
Q

examples of application of inhibitors

A

petroleum industry
packaging industry
sour gas systems
potable water systems
engine coolants

40
Q

environmental types of corrosion inhibitor

A

neutralizer
scavanger

41
Q

adsorption (mixed) 2 types of corrosion inhibitor

A

chemical
physical

41
Q

inorganic 2 types

A

anodic
cathodic

41
Q

green 2 types of corrosion inhibitor

A

extract
oil

41
Q

2 cathodic types of corrosion inhibitor

A

poisonous
precipitation

MATERIAL SCIENCE and ENGINEERING (8 decks)

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