as thee lectrond onor andt he metala st he electron acceptor,h as been
postulated.
21
3.4.3I nteractions between Adsorbed Inhibitors
When the coverage of the metal surfaceb yt he adsorbed inhibitor species
increases, laterali nteractions betweeni nhibitorm oleculesm ay arise,
influencing efficiency.
Attractive lateral interactions usually give riset os tronger adsorption
and higher inhibition efficiency.T his effect has been shown in the case
of compounds containingl ong hydrocarbon chains, because of attractive
van der Waals forces.
22,23
In the presence of ions or molecules containing
dipoles, repulsive interactions may occur,w eakening the adsorption and
diminishing the inhibiting efficiency.
3.4.4R elationships between Inhibitor Reactivity and Efficiency
The nature of the inhibitori nitially present in acid solutions may change
with time and/or the electrode potential as ac onsequence of reduction
reactions, polymerization reactions, or the formation of surface products.
The inhibition because of the reaction products is usually called secondary
inhibition, whereas, primary inhibition is attributed to the compound
initially added to the solution. Secondaryinhibition may be higherorlower
than primary inhibition, depending on the effectiveness of the reaction
products.
24
An exampleofinhibitors undergoing electrochemical reduction is that of
sulfoxides, the most important beingd ibenzyl sulfoxide, whose reduction
gives rise to as ulfidet hat is more effective than the primary compound.
25
On thecontrary, thereduction of thiourea andits alkylderivatives give rise
to HS
K
ions,whose accelerating effect is known.
26
In some cases, thereduction
reaction maybefollowedbypolymerizationreactions at themetal/electrolyte
interface. This mechanismo fa ctioni sg enerally accepted fora cetylenic
derivatives.
27,28 Electrochemicalm easurementso ni ronelectrodes in sulfuric
acid solutionsi nhibited by alkynes
29
showed that acetylenic compoundsa ct
as cathodic inhibitors,g ivingr iset oasurfaceb arrier phenomenon.D uwell
et al.
27
foundh ydrogenation andd ehydrationr eactionp roductsi nh eptane
extracts of acid/ironp owder/ethynylcyclohexan-1-ol.A ccording to Duwell
et al., the efficiency of ethynylcyclohexan-1-ol as ac orrosion inhibitor
apparently dependso nt he properties andr ates of formationo ft he reaction
products.P utilovae ta l.
28
used as imilar extraction techniquet os howt hat
acetylener eacted at thei ron/hydrochloric acid interfacet of ormt hick
polymolecularfi lmso nt he iron.P odobaeve ta l.,
30
analyzingt he results
obtained foralargen umbero fa cetylene derivatives, concludedt hatt hese
compounds act according to an adsorption-polymerization mechanism;
thea dsorptiono ni ront akes placem ainlyv ia at ripleb ond. Accordingt o
Podobaev et al.,
30 thep resencei nt he molecule of polarg roupsw eakens
Corrosion of Linings and Coatings
62
CAT8247—CHAPTER 3—6/10/2006—19:23—KADAMBADI—XMLMODEL B–p p. 55–68
postulated.
21
3.4.3I nteractions between Adsorbed Inhibitors
When the coverage of the metal surfaceb yt he adsorbed inhibitor species
increases, laterali nteractions betweeni nhibitorm oleculesm ay arise,
influencing efficiency.
Attractive lateral interactions usually give riset os tronger adsorption
and higher inhibition efficiency.T his effect has been shown in the case
of compounds containingl ong hydrocarbon chains, because of attractive
van der Waals forces.
22,23
In the presence of ions or molecules containing
dipoles, repulsive interactions may occur,w eakening the adsorption and
diminishing the inhibiting efficiency.
3.4.4R elationships between Inhibitor Reactivity and Efficiency
The nature of the inhibitori nitially present in acid solutions may change
with time and/or the electrode potential as ac onsequence of reduction
reactions, polymerization reactions, or the formation of surface products.
The inhibition because of the reaction products is usually called secondary
inhibition, whereas, primary inhibition is attributed to the compound
initially added to the solution. Secondaryinhibition may be higherorlower
than primary inhibition, depending on the effectiveness of the reaction
products.
24
An exampleofinhibitors undergoing electrochemical reduction is that of
sulfoxides, the most important beingd ibenzyl sulfoxide, whose reduction
gives rise to as ulfidet hat is more effective than the primary compound.
25
On thecontrary, thereduction of thiourea andits alkylderivatives give rise
to HS
K
ions,whose accelerating effect is known.
26
In some cases, thereduction
reaction maybefollowedbypolymerizationreactions at themetal/electrolyte
interface. This mechanismo fa ctioni sg enerally accepted fora cetylenic
derivatives.
27,28 Electrochemicalm easurementso ni ronelectrodes in sulfuric
acid solutionsi nhibited by alkynes
29
showed that acetylenic compoundsa ct
as cathodic inhibitors,g ivingr iset oasurfaceb arrier phenomenon.D uwell
et al.
27
foundh ydrogenation andd ehydrationr eactionp roductsi nh eptane
extracts of acid/ironp owder/ethynylcyclohexan-1-ol.A ccording to Duwell
et al., the efficiency of ethynylcyclohexan-1-ol as ac orrosion inhibitor
apparently dependso nt he properties andr ates of formationo ft he reaction
products.P utilovae ta l.
28
used as imilar extraction techniquet os howt hat
acetylener eacted at thei ron/hydrochloric acid interfacet of ormt hick
polymolecularfi lmso nt he iron.P odobaeve ta l.,
30
analyzingt he results
obtained foralargen umbero fa cetylene derivatives, concludedt hatt hese
compounds act according to an adsorption-polymerization mechanism;
thea dsorptiono ni ront akes placem ainlyv ia at ripleb ond. Accordingt o
Podobaev et al.,
30 thep resencei nt he molecule of polarg roupsw eakens
Corrosion of Linings and Coatings
62
CAT8247—CHAPTER 3—6/10/2006—19:23—KADAMBADI—XMLMODEL B–p p. 55–68