chpt 12 inhibitors (intro to corrosion book)

Question 1

a substance which retards or slows down a chemical reaction.

Answer 1

chemical inhibitor

Question 2

a substance which, when added to an environment, decreases the rate of attack on a metal

Answer 2

corrosion inhibitor

Question 3

corrosion inhibitor works by adsorption of thin film that

Answer 3

retards corrosion

Question 4

corrosion inhibitor works by Forming thick bulky precipitates that coat the metal and protect it from

Answer 4

attack.

Question 5

corrosion inhibitor works by causing the metal to corrode in such a way that a combination of adsorption and corrosion product forms a ____ ____

Answer 5

passive layer

Question 6

corrosion inhibitor works by causing conditions to be more favorable for formation of _____ _____

Answer 6

protective precipitates

Question 7

corrosion inhibitor works by removing aggressive _____

Answer 7

constituent

Question 8

6 types of corrosion inhibitors

Answer 8

passivating (Anodic) inhibitors
cathodic inhibitors
ohmic inhibitors
organic inhibitors
precipitation inducing
vapor phase

Question 9

also known as anodic inhibitors, cause a large positive shift in the corrosion potential (passivate the surface)

Answer 9

passivating inhibitors

Question 10

two types of passivating inhibitors

Answer 10

Oxidizing (absence of oxygen)

Non-oxidizing (presence of oxygen)

Question 11

three main types of cathodic inhibitors

Answer 11

cathodic poisons
cathodic precipitates
oxygen scavengers

Question 12

______ ______interfere with the cathodic reaction

Answer 12

cathodic poisons

Question 13

_______ ______precipitate on cathodic areas to increase circuit resistance and restrict diffusion of reducible species to cathodes

Answer 13

cathodic precipitates

Question 14

______ ______ prevent cathodic depolarization caused by oxygen.

Answer 14

oxygen scavengers

Question 15

AKA gunkers. increase the ohmic resistance of the electrolyte

Answer 15

ohmic inhibitors

Question 16

Ohmic Inhibitor Film deposited on anodic areas

Answer 16

corrosion potential shifts to more positive values

Question 17

Ohmic Inhibitor Film deposited on cathodic areas

Answer 17

corrosion potential shifts to more negative values

Question 18

Ohmic Inhibitor Film deposited on anodic and cathodic areas

Answer 18

corrosion potential shifts slightly to either direction

Question 19

cannot be strictly classified as anodic, cathodic, or ohmic. very thin films, usually on a few mm thick. affect the entire surface of a corroding metal when in sufficient concentration.

Answer 19

Organic Inhibitors

Question 20

scale formation over the entire surface. most common types are silicates and phosphates. combination of both anodic and cathodic effects.

Answer 20

precipitation inducing inhibitors

Question 21

AKA volatile corrosion inhibitors. it is vaporized into a gaseous form. Inhibit corrosion by making the environment alkaline

Answer 21

Vapor phase inhibitors

Question 22

9 dissolved species

Answer 22

oxygen            chloride
sulfates            bicarbonates
sulfides             metal cations
acids                  alkali
gases(H2S, CO2, Ammonia)

Question 23

inhibitor application methods

Answer 23

Continuous injection
batch treatment
squeeze treatment
volatilization

Question 24

safety precautions

Answer 24

MSDS
Disposal
Possible effects– heat transfer, foaming, emulsions, plugging, other limitations (temp, pressure)

Question 25

all three components of a corrosion cell are affected by a corrosion inhibitor to retard corrosion

Answer 25

Anode, Cathode, Electrolyte

Question 26

the inhibitor may cause

Answer 26

increased polarization of the anode (anodic inhibition)

increased polarization of the cathode (cathodic inhibition)

Increase the electrical resistance of the total corrosion cell circuit by forming a thick deposit on the surface of the metal

Question 27

to treat (a metal) to render the surface less reactive chemically

Answer 27

passivate

Question 28

Nonoxodizing passivators are also dangerous when used in insufficient amounts because

Answer 28

the oxygen that is required for passivation is a good cathodic depolarizer.

Question 29

corrosion in non aqueous liquids such as fuel, lubricant, and edible oils is usually caused by small amounts of

Answer 29

water that is present

Question 30

most important class of organic corrosion inhibitors

Answer 30

Organic amine

Question 31

used for water supplies, oil-field injection water, once-through cooling water

Answer 31

continuous injection

Question 32

a quantity of inhibitor is added at one time tor provide protection for an extended period of time.

Answer 32

batch treatment

Question 33

a method of continuously feeding an inhibitor into an oil well. Inhibitor pumped in followed by sufficient solvent to force the inhibitor into the formation.

Answer 33

squeeze treatment

Question 34

it is transformed into a vapor

Answer 34

volatilization

Question 35

To apply cathodic protection to a structure, the objective is to force the entire structure surface exposed to the environment to ______ current from the ________.

Answer 35

Collect

Environment