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CORROSION IHHXBXTIOK WITH QUATERNARY AMINES
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Major Professor
/ i . / j Minor professor
6 ^ ^ , o l ^ h ! f t e » . n t ol ( W . t r y
• i > .n n T - y * v' * r v 1 -f • *7 1 *" I • n1 • " ,* V " '•T Mi? Q , J \ r , u J . U „ , J ; •' i J j - » } . . x \ ' - * * J - a - „ -J - , - —•5* t Y h Y 1 * l-- -J O
- 'J # ^ J *J
" . ' r a s e * ' t e d t o t b o C S r a ' I n a t s C o u n c i l c p s h e
Jiorth ' 3 ' e x . i s Sza g - s U n i v e r s i t y i n P a r t i a l
7 u l f i l l n e n t o f t h s T e o u i r s i A e n f c s
< o r u n e i - e ^ r c e o . t
> q f p r ' 'T> / \ f y r j p y r - » - v y p 71 y 3 r £ , R Y "
E v
H a h i b K a i s z a d e h , . " 1 . 3 .
JO n t o r . , T a x a s
A u g u s t , 1 9 6 9
Y Y 'T* ,•? ~ T'f |
Psq r sac t i cna *r>7olvs».i -yhm "> s t e s l co'jtk": i s plseftd
ir. acid so lu t ion . One 1o Iron -iis-solution ~<rd the other r s -
fctdor, i c hydro ~-«n ;--vol-.:.-.2 rru I'scse occur s t d i f f e r s 3 t 5 i tos
01? :; be "X'tr.l, vhich .*rs s £ to ;? a "* 1.oor 1 rothc'd.**1' .-ind
"IockI r . * e d «Ptvn;
F© -—r» fV''^ * 2e " /.no;J c 1 a c t i o n
v»fc + + »» Ifn Cc.thndic "'e action *•>
Tzi' e\tU*l i t is 3t the c'n.nie tos t sorrow for, take,-? and
both tho rnotfic and c&tuoctic roaeui ouj occur in -via ;vi©.
u.tic""> "U t-h§ vsfcr.l surt'aco (X). -berpfora, i>-etsl ^urlNes con.
sistR of "i?nj rn vv.!ie~cfithod:i.c c e l l s which are loc-:.uis*ac1 opc!
control c crroBior. sJt, i n l s ? s ;.f'P(;"tirx?'C ..:'C i*',*'rroc!
to m n 'T.-.'Jjrsci-pot'.v fcial;: 5 /0ten,
•'b&rofare-, in order t vtucy ate e l corroding in ac ids ,
i t is no co.asn.ry to do so i»> i e n s c-i* t*-'o ^er.-*<rt't£
alocDr«>ch6<£S<x& r^ieif, oro. T« jyrfcicuJert -0 ere infewrerstw?
in liov ur v ouriusl 70 to. t3 n l r, ro l l ed to the ore r>iec« of
s t e a l v-ill e f f e c t ths two individual rood:. or.r», a:t-i how
ore::.icc?.:5 ( inh ib i to r s ) «d^od to the j r i d . i f fee t t!v*«e r e -
ac t ions , appl ica t ion of a po t en t i a l Crc<i" outside slo^s
ur, cne sml ^pe&da up the o the r , cy unir.a. £ reference e l e c -
trode system, w* can t e l l how ths of the corroding
•>te®X i s dh-mvLug fro;.i i t s o*>c>'.-circuit value#
These changes of potential with an externally applied cur-
rent are called "polarization curves»n and characteristics
of these curves can be related to the Individual iron and
hydrogen reactions.
O.C. Potent/wl
x'.ev re iQV np
igure {A}
5leefcroc hemical Background
Fifvre (A) shows the anodic and cathodic polarization
curves; the forraer is to the right and the latter is to
the left. At point K, there is no current applied. If an
external current io applied to increase the anodic current,
mere iron goes to solution «s iron ions, and fewer hydrogen
ions are converted to hydrogen molecules(curve AB).If polarity
i s reversed, and oathodie current i s used, more hydrogen ions
w i l l . o to hydrogen molecules and l e s s iron i s d isso lved
in the so lut ion es i ron (curve CD). ;vfc po in t A, there i s no
i ron d i s s o l u t i o n t a k i n g p lace , arid only hydrogen evolut ion
occurs . This po in t ir. r e f e r r e d t o as "Heversable Iron, '?
At poin t C, t he re i s no hydrogen evolut ion, arid iron d i s s o l u -
t i o n i s t a k i n g p l a c e . This point i s ca l l ed "Revers ible
Hydrogen." Somewhere in between r e v e r s i b l e hydrogen and
r e v e r s i b l e iron^ t he re i s a po in t where i ron d i s s o l u t i o n and
hydro£an evo lu t ion r a t e s a.r.j t he ssme ( l i no i?G)» 'Jljctrapo-
la t ion of t h e U n a s AB and CD i n t e r s e c t s the v e r t i c a l p r o j e c -
t i o n from the co r ros ion p o t e n t i a l Kf and a t t h i s poin t two
r e a c t i o n s are occurring; with the s. me r n t e . Point; & i s
c a l l e d ''Open C i r c u i t P o t e n t i a l " av,6 p o i n t s F and G a r e
referred t o as ftOp;ni Circuit Current" f o r anodic and cathodic
p o l a r i z a t i on curve,
I f an i n h i b i t o r i s added, one of sev«r*l thinrc, :my
occur : e i t h e r the nlope of 3 changes, or the ha I f - r e a c t i o n
nob<am t i a l s h i f t s , or an ohnic res i s tance i s introduced, o r
Rome combination of t he se occu r s . The cso verne nts of these
p o t e n t i a l s and the changes in t he se polarisat ion carves a re
normally -xasured a g a i n s t a reference e l e c t r o d e whose po-
t e n t i a l i s knovn (usually a s a t u r a t e d calomel e l e c t r o d e } .
The word ' 'cathode" r e f e r s t o an e l e c t r o d e a t which
currei t e n t e r s to the e l e c t r o l y t e , and "anode , r as the
e l e c t r o d e a t v-hich cu r r en t l eaves the e l e c t r o d e and
. . . . . . 4
returns te the electrolyo-3. A.? nenUoa^d before, at the
open circuit potential, the rats of oxidation of iron is
equal to the rate of reduction of hydrogen ions.
I (iron) - 2 (hydrogen ion)
If current is impressed on e cell from o.n external
source, such as n potent:' ostat cr battery, the steady state
potential is disturbed, and the above equilibrium no longer
exists. The difference between the Actual reversible and
irreversible potential is called overvolta^e. The Irrevers-
ible potential of an anode is riore positive than its revers-
ible potential. l'!hen the applied potential is infinitesi-
mal ly more positive than the reversible potential of the
electrode, v.'e have
S} ancde
irreversible ~ £ rev, +)|anodic
where is anodic overpotential.
If the external potential is only infinitesimally more
negative than the reversible electro-ie potential, it can be
written as
S cathode
irreversible « ? rev. -^cathode.
Plots of the external current vs. the overpotential,,
are colled "polar!?at3on curves,n r.nri the effects of in-
hibitors on these curves can he interpreted in terms of
which cf the two electrochemical reactions is changed.
Adsorption background
Inhibitors (usually organic nitrogen compounds) added
5 t o t h e ac id may become a t t ached t o t h e mata! s u r f a c e
(absorbed) and a f f e c t on? or both of t h e VMQ e l e c t r o -
cheraic*il r e a e t i o r i s .
There a r e tvo t ypes of a b s o r p t i o n by j?etal s u r f a c e J on©
i s '/an dar , , ;aal f o r c e s of a b s o r p t i o n , ^irlch a r e P h y s i c a l
f o r c e s | the o t h a r on<? i s ch enseal -i9-sorption (cho?Ri s o r p t i o n ) ,
which forma chcmictu bonds between organic compound and
roe t a l s u r f a c e . Physical adsojption i s pen o r a l l y accompanied
by smal l heat change, t h a t 5s , 5 kcn l or Xc^ss pef r . c le ,
Kbil© in chemical adso rp t i on heat involved i s f r c n 7.0 t o
IOC' kca l per mole.
The mechanism cf a d s o r p t i o n of i n h i b i t o r s on meta l
wurf&ce coulo be by e i t h e r p h y s i c a l ?.dsorption or chemi~
s o r p t i on » In n i t r o ^ e n - c o n t a i r j n.p crnr>ounds where t h e r e i s
a f r e e p a i r of e l e c t r o n s , the e l e c t r o n d e n s i t y on the n i -
t rogen and i&a a v a i l a b i l i t y cauae a bond format ion between
Es©tal s u r f a c e and organic TiolecaJ as by s h a r i n g an e l e c t r o n
p a i r from the i n h i b i t o r U ) . This i s r e f e r r e d t o s s "chem-
i c a l adsorp t i o n , v h e r e n» s a j s e t s as an a c c e p t o r , E.nd i n h i -
b i t o r as s donor . Tr qua t e rna ry aarnoniup coripounds, t h e r e
i s no f r e e e l e c t r o n p a i r p r e s e n t , and o rgan ic i n h i b i t o r e x -
i s t s in ac id s o l u t i o n s s c j ^ i on ^ ? } if ) am* n i t r o g e n has
for.vtal o o s i t i v a charge as - 3 , vhere R could be any
a r y l or a l k y ! group. In such a case where n i t r o g e n i s pos-
i t i v e , i t ^us*o bo adsorbed p h y s i c a l l y on the -natal s u r f a c e ,
and forms a f i l m , by v i r t u e of e l e c t r o s t a t i c a t t r a c t i o n ,
Th is a d s o r p t i o n should occur a t t h e l o c a l ca thode , s ince
6
a t t r a c t e d t h e r e . There i s d i r e c t relationship between
t h i s f i l n r e s i s t a n ce and i n h i b i t i o n e f f i c i e n c y (5*6) . I f ,
however, the I n h i b i t o r s e x i s t as f r e e amines in s o l u t i o n ,
they should adsorb a t v,he l o c a l '-mods ( ? ) . In {-est i n h i b i -
t o r s in ,-;cid s o l u t i o n s , t he re i s an equi l ibr ium
mTT ' . rr^ • • >• •; \f t; T i : i 2 ' • - < i " " L r j
so t h a t e i t h e r the f r e e so font. {£'?.'It-,) or t h e ca t ion form 4~
(RNH, ) could , ? s o r b , nnd the ?^uilibri"J«a vpuld be d i sp laced 3
to r e r l e / n s h the supply . fTcwsver, 2or '^uateraory compounds
•n > f r* -} -» u , i v u J~
h t h e r e can be no equllihiduKi, sad the adsorp t ion ought t o be
j u s t p h y s i c a l , ;nd. only t h e l o c a l cathodes should be e f -
f e c t e d . The purpose of the p resen t work wss t o s tudy the
e lec t rochemica l and ' .nMMt?on e f f e c t s of s e v e r a l qua te rna ry
compounds in the ."cid cor ros ion of s t e e l ,
Quaternary arr iot iun conpounds ere s a l t s and a re very
so lub le in noct of the advents. '7 ha t i s t-hy •'» wide range
of concen t ra t ion of then can be used vithout any d i f f i c u l t y .
The r e c a n t s t u d i e s cf these coypouncs have r epo r t ed t h a t
JvT-alkyltrir«iethyl~aa*nonii!.^ bronide i n h i b i t s the acid d i s s o l u -
t i o n of the s t e e l ( ' ! / , The degree of i n h i b i t i o n increased
vd th al 'cyl chair l e r ^ t h ^et^een k nnd X* cs»rl>on a tone . T'o
po l i r i ca \ t l on curves ' ' ;ere given ?n t h i s s tudy ,
•i xj i^ri n t a 1 r> y o c e d n r e s
The tnaId s t e e l coupons which were used throughout t h e
experimentts had approximate s ize of 25raw x 60 iwit wi th one
millimeter thickness. Coupon? were allowed to suspend in
acid solution by r rod and ?bout 20 inches' in total area of
che coupon *?£g exposed to the solution. The acid used was'
2.0 MH CI ,-;t 60 degrees centirrade. The coupon surfaces were
polished -.Tilth Tine ea»ry -nsper, rinsed In r.-cetone and dis-
tilled water. Figure (H) s'iows the e-xporimental apparatus
T.'Il 1 c h w o s -,i c d .
Potent!ostat
register
-Jit
Reference Electrode
oacter^ oalt Bridge
6
r'i. ure i t )
Two' different procedures were used to determine the rate
of corrosion. In the first method the hydrogen gas evolved
was collected in a <*as burette and the volurre was measured
at given tit.ie intervals. Periodic rate determination was
plotteo for cathodic-aiio&ic polarisation in elcdtrochemical
process. Fron this rathod, the ai-ioant of iron converted to
iron chloride could be determined. This method of rate
determination was best, and it was used especially in cathodic
polarisation and also where the corrosion rate was high, as in
the case where no inhibitor was present.
3
The second method was; the d i r e c t weighing of the meta l
coupons on an a n a l y t i c a l b a l a n c e . The coupon was removed
from a c i d , r i n s e d wi th s c e t o n e , and weighed. Test b o t t l e s
used con ta ined about 200 ml of »c id s o l u t i o n (£NH CI ) , which
were p laced in a oons ton t - t e n n e r a t u r e o i l ba th mainta ined
a t 60 degrees c e n t i g r a d e , Workirtp e l e c t r o d e and calomel
r e f e r e n c e e l e c t r o d e were arranged t o be c lo se t o each o t h e r
in t h e f i r s t b o t t l e . The second b o t t l e w s connected t o the
f i r s t one by s a l t br idge :"or e l e c t r o l y t i c c o n t a c t . Pla t inum
e l e c t r o d e waw placed as counter e l e c t r o d e in the second, b o t -
t l e f o r complet ing t h e e l ec t rochemica l c i r c u i t . An o u t l e t
f o r hydrogen gas e v o l u t i o n was ar ranged t o r o t p e r i o d i c
b u r e t t e r e a d i n g s . Uninh ib i ted p o l a r i z a t i o n curves were run
and the r e s u l t was compared wi th i n h i b i t e d p o l a r i z a t i o n
curves f o r co r ros ion r a t e c a l c u l a t i o n s .
The I n h i b i t o r s used were p y r i d i n e q u a t e r n a r i e s of s e v e r -
a l d i f f e r e n t c h l o r i n a t e d hydrocarbons . The p r e p a r a t i o n ana
p u r i f i c a t i o n of t h e s e compounds a re desc r ibed in the appendix .
!csi.i 1 r,.-md. Discune5ons
Experiments showed t h « t t he a v e r s e "J OS3 of " 'e ta l i n an
u n i n h i b i t e d s o l u t i o n was 5,13 ± 0 ,?6 -rig 1 car I h r . , xbHe in
i n h i b i t e d acid s o l u t i o n i t cons ide rab ly l e s s than t h i s
obtained, v a l u e , depending on t h e type of i n h i b i t o r used . A
number of d i f f e r e n t qua te rnary ammonium compounds were used
as i n h i b i t o r s . I t turned out t h a t hexadecyl nyridiniurB
9
chloride was the best one in uhe -toup, with the percentage
of inhibj ti on up to 99-1- in 100 ppw acid solution. The list
of the uood confounds are A3 "ollows i/ho CI"* anion is
1 ot sh own.):
Benzyl Pyridinium Chloride
<j>- GH«j P-Methyl Benzyl Pyridinium Chloride
C, Hq P-Butyl Benzyl Pyridinium * y C&oride
^-N-CH - CdH-i 7 P-Octyl Benzyl Pyridinium 2 ( Chloride
N~ CH0CH?~/ Phenyl Ethyl Pyridinium ^ ** ' Chloride
N- (CHg) 2.5 Hexadecyl Pyridinium Chloride
The first tv/o inhibitors were very poor inhibitors# In most
easel; it -was impossible to determine the inhibited corrosion
rate since it vr-a no close to the uninhibited corrosion rate«
Phenyl ethyl pyridinium chloride was a better inhibitor than
either of ihe above :.*Qr*tioned compounds, but stili it was not
considered as a ;-:ood inhibitor. 1g h«i> the ,.:ai»e rao.lecular
weight as P-mebhyl bor.s/1 pyridiniu.i chi.-iide, but. is much
more efficient. He..'ever, the additional length of aliphatic
carbon chain next '00 nitrogen say rake r; difforence in the
efficiency,
'-.'itbill the other three organic compounds, hexadecyl
pyridinium chloride was tn excellent compound and even effec-
tive in concentration 03 lev as C.10 IPK, Table 1 shows its
10
effectiveness in low concentration and also in comparison
to otter inhibitors,
TABLE 1
..kiiik if xv'l AC'il' 'i; • •<;' i! ' !1T A TSK NAP.Y XII "OK IUF
Concentration 1 PPK
Compound 1,000 100 10 1 1 0.01
Bensyl Pyridlniuxa Chloride
0.76 0.17 31 i frhfc nil nil nil
2-Benzyl Pyridine 0.92 o.g? 0.75 0.20 nil nil
Hexadecyl Pyridinium Chloride
0,99~r 0.99 0.97 0.35 0.13 Slight
Typical weight; loss-time curves for two of these com-
pounds in 2.01", I-ICl at 60 C are shown in figures 1 and 2.
T he s e u & t h i 11 u s t r a t e :oint which often causes considerable
uncertainty in interpretation, namely the invariant (Figure l)
versus the continuously varying: (l''i&rure 2) corrosion rate.
For well inhibited so.iut.icns, ic is not at all uncommon to
obtain invariant rates, while for uninhibited and poorly
inhibited solutions, it is usually impossible to fix a sin-
gle value of the rate for a reference value. In this
11
particular work, a mora or lass steady rate obtained after
several hour3 of corrosion in calculating par cent inhibi-
tion values, although it is doubtful th.it the real surface
area after this much oStack is corjparoble to fche .real sur-
face a/ea being corroded in the v;ell-inMbiosd solutions.
-•-jrd and JUg^s (?) have ~ho-'-n that se"-e improve :nent in repro-
ducibility of per cent inhibition velues can be obtained by
allowing the c out: on to corrode freely in the uninhibited
solution for several minutes before the inhibitor is added,
and then relating rates obtained irmediitely before «>nd ini<»
mediately after the add?!tion. while this increased repro-
ducibility is desirable, it requires considerably more
experimental effort, and vould not a'"d significantly to the
present study, x'hieh is locking primarily for relative ef-
fects between compound types.
Inhibition rvta for t o of the compounds tested are
shown in Figures 3 joid as ;> function of concentration.
Similar data were obtained for the other compounds; the
data shown v;re chosen zo 11 lustra to the wi-5e variation in
inhibition levels "-:hile retaining the snao ":enerel function-
al dependence concentration. 0 is the fraction inhibition,
1 ~ Inhibjted Ti ate, and ,?a.~ bo t^-c-ht ,sf is the corrosion
llninliTbited Mate
analog of the frfcesi on of aarf&ce covered by adsorbed mole-
cules in the tian.jiu.ir adsorpMen isotherm. Hoar -md Holliday(tf)
first treated corrosion data in ter>.ir> of this isotherm, and found that for gos;e inhibitors a plot of log §
1-0 versus log (inhibitor co a centrati on)gave a straight line of slope
12
O X
X X
^ CL
W3/9W 'SS01 J.H913M
13
00 ( J j
CC C9
o o o o "sj- rO
I A I < * \ /C\ I A I 1
,:-CV • Mr • A
I \ ,
m o
15
ID l±J CO o
16
1 . 0 , in agreement with the Lanrir.uir t h e o r v . The da t a on the
q u a r t e r n a r i e s do not fo l low t h i s t r e a t m e n t , but i n s t e a d show
l i n e a r behavior 'when 6 i t s e l f i s p l o t t e d v e r s u s log
( c o n c e n t r a t i o n ) . Ho i n t e r p r e t a t i o n of t h i s behav io r in terms
of i so therms can be o f f e r e d a t the p r e s e n t t i n e .
Table 1 paves t h e maximum va lues of 6, and the
c o r r e c p e n d i n v ; l u . e s of 6 , which could fee ob ta ined f o r 1 - 5
each i n h i b i t o r t e s t e d . I t i s i n t e r e s t i n g t o note how t h e
use of t h e f r a c t i o n 6 he lps to n spread ou t" the a f f e c t s of s t r u c t u r e i n the b e t t e r i n h i b i t o r s . Thus. goes from
6 i t o 124, or doub le s , aa C i t s e l f goes from 0 .9^5 t o 0,992 .
In view of the l i n e a r i t y of t h e 6 dependence on log C, and 1-*?
a l s o because of t h e importance of the f r a c t i o n ,
covered s u r f a c e in adso rp t i on t h e o r y , i t i s f e l t t h a t a uncovered' s u r f a c e
more meaningful i n t e r p r e t a t i o n of the d a t a can be made when
they a r :• analyzed in terras of t h i s f u n c t i o n , r a t h e r than in
t e r a s of per cen t i n h i b i t i o n a l o n e .
TABLE 2
SUff'IARY OF MOLECULAR .STRUCTURE EFFECTS OF ;/0i\RTSlthARr,C3 C N iiiKIBITION
Quaternary 0m ax ce / i - e j " max, C jHsf H3 6". ?5 3
C5!l5r^GH2-C6H4«C4H9 . —
'"" £ 0 ' "
c5H5n+~dH2 i 6 % - c ^ r i 1 7 ' d .992 12 £
C5JI5HK.CH2CH2-66H5" ' 0.9S5 ' ' ' 61 '
C5H5N+-(CH2) 15-0:43" "° (5.993 1 ' 125
17
i t WS5 e\^pect^G a t he bogi'.niiii}*; ot t h i s vTork cha t only
xhe hydrocarbon ch v ; rac tur o r t h e i n h i b i t i n g a o l o c u l o would be
a ugt©Tiuxi\xng iac~oor in xniixoitxcii ofxUciuTicy, iint th&fc hydro-
carbon cli£ir &c t s r Vvoujid bo pyxTip J.y uBooncorit oh tbo wunbor ox*
carbon v- co*. is in ±iu c ic^x/i c.<% g gc. cliwa t o the pyr; d ine n i t r o g e n
afcora. T;,e t a o i s f o r orpuctsroion v:aj sunt s i nce those
iiiolecuxe-s d ia noc rave i're-3 e i o c t r c n ,.-airsf f/hc a d s o r p t i o n
p roces s 'would bo pure J . physic?.! :nri. tho •nn:iy s u b t l e f a c -
uOi's ox iiioleculeir utrnefcurt? vn'iich luwhcs tli6 c1 3mi s o r p t i o n
bond wo uld oo c.. no e / ' . a c t« .'.-ale "Ciio s t r u c t u r a l f a c t o r s ax -
amine a in the prer-wu t s c r i e s oX* compounds 3:r > 1 i n i t e d , the t a -
b l e shows tha y l o c a t i o n or t he phenyl pro up r e l a t i v e to t h e
q u a t e r n a r y n i t r o g e n i& a s i g n i f i c a n t f a c t o r in t he i n h i b i t i o n .
Thus, f o r the sane hydrocarbon number, C^Hr-Cl^GHn, t |fe a r -
rangement Ki th one Clig b^ive&u the p y r i d i n e n i t r o g e n and the
phenyl givup y i e l d s a mucn poore r i n h i b i t o r oh an che a r r a n g e -
^iftno ^ i t t " oouii onyione groups bet'wceu the tv;c aror.iotic
i^roLiuty* j-ii(se&oigciox oris 01 o^her sorucGursi. e f f e c t s In q u a t e r -
na ry types a r - con t inu ing*
i^lec troche^ni ccj. intrasurementa, p r l u i a r l i y the s h i f t in cor~
iColOii pOvtUti.e i vK'O Oxl© CilOIlg^S 1X\ oiOpO8 Ox t li6 l og (cUIT*@Ht
d€H 511y j j po hoi t i '=• 1 c uvve 3 13, £01 s i 0p0 s) c & 11 bs in t s r p r 6 t s d
in C6r*vAj 01 tn€ re1&civ0 <2i f ec t s of tho i n h i b i t o r on the <2 no—
d i e or ca the d ie s i c e s ox the co r roo ing s u r f a c e * Again $ based
011 a d s o r p t i o n t h e o r y , oi\e './ould expec t t h a t the q u a t e r n a r i e s f
with t h e i r f o r m a l p o s i t i v e charge $ would adsorb p r e f e r e n t i a l l y
IS
on cathodic sites and ,rive a potential shift toward the re-
versible Ire/Ve !half-cell (jL.s,., sr. **ai:or*ic sl\i ft") . This
was not observed by *xrJvins (/-) Mit:i the ternary bromides
in K^SO^ * nor by ua \;5 fch qj^atorwu-y cMcri :L~ trCl. Fig-
••ire 5 shows the magnitude ox the ihift in eor.rc-r>ion potential
as a function of coaeaaorasi en or -?wy-;<'3-,cyl pyridiniitrr. chlo-
ride, and that j.t is in 'the direct,!OK of thn reversible hydro-
gen electrode, thae a "'oc thoiic shift»•' Mei-cins' values for
the quaternary broMiaeo in ft ^rve c. v«ry similar concen-
trate. on behavior, cut n generally libber totcl potential-
shift (00-70 -fiv c-t 10~2 vs cur 30) » >hother the different
magnitude .nay be an effect of the bromide 5or? vs. the chlo-
ride ion, or of a counter ion In the ir.b3h3tor different from
the acid anion, which would seem to he cc-strained to adsorb,
physically, early idv<s the cathodic ,-jhift vhich has long
been a primary arg>i;aont ror ii'< j;uierption.
A second e 1 e e t r o c h e-a i e el n*ea sure ."inert oft^n used to
characterize inhibitor* actimi in th'-; change :.r Tafel slope
upon addition of the inhibitor. lie suit 2 for ?0~ppn
n-hexaoecyl pyridiniaa eblovidc are •:!h"'--,n In "•''i.friires 6 nr.d 7
for c&thodic pol«riii® ul ••.uzn, arid in % ^nd 9 for anodic
polarizations. IVe >c carves '-ere v<.n by surin?; both,
the net external current (r,;,e usual polyH nation curve) and
the partial (or :-}aj.f-coll; current by ehe.nical analysis.
Measurement by ciieifdcol ^nalysis caro.ee the polarization
curve for each half-reaction well down into the corrosion po-
tential regi.cn, in fact, past the open circuit corrosion
• ELECTRODE POTENTIAL, VOLTS vs, S.C.b. , ' ' CJI 'r>
I 0) o
rJ o o -J, O)
( ) )
o u
r > 5 —l en -< o
o n 'j
x m x >
i Oi
i a 4 rn q o ° -< r
"U i ~< OJ E9 cn o
i OJ o
c
o X r~ ° i 3! ro o en n
ro D
i Ol f\) o
' I
I On Oi
ai d
i i
ov 0 01 "T
o o ~T~
CO • Ol
— , —
I 19 Irs CO o I
o m o
33 Ol
O X CO
20
FIGURE 6 CATHODIC POLARIZATION
STEEL IN 2.0N HC1 ©FROM NET CURRENT xCHEMICALLY FROM
; -3.0
--4.0
CO IT.
-0.80 -0.70 -0.60 -0.50 -0.40 POTENTIAL, VOLTS vs. S.C.E.
-0.30
21
2,0 FIGURE 7
ANODIC POLARIZATION STEEL IN 2.ON HCI FROM NET CURRENT CHEMICALLY FROM Fe
3.0
4.0
5.0 CPrr,
I
•0.70 •0.60 -0.50 -0.40 -0.30 POTENTIAL, VOLTS VS. S.C.E.
-0.20
22
-2,0
N ;>
or CL | -3 .0 «•* >-
b-C0 z: LU O
Z4A LU ct: cr ZD o C9 O
-5,0
FIGURE 8 CATHODIC POLARIZATION
STEEL IN 2.ON CI -t-20ppm n-C|sH33N'C5H5CI
J_L •0.80 •0.70 -0.60 - 0.50 -0.40
POTENTIAL, VOLTS vs. S.C'.E.
2.0
23
N
or CL | - 3 . 0
> -
t CO 2 LU Q
z - 4 0 1 -LU (T (T 3 O e> o
-5.0 -
FIGURE 9 ANODIC POLARIZATION
STEEL IN 2.ON HCI'+ 20ppm n-C|6H3 3N C5H5CI
-0 .70 -0 .60 -0 .50 -0 .40 - 0 . 3 0 POTENTIAL, VOLTS vs. S.C.E.
- 0 . 2 0
. . 24
p o t e n t i a l . This i s p o s s i b l e because the two L u l l ' - c e l l r e -
a c t i o n s which melee up the t o t a l c o r r o s i o n r e a c t i o n a re
a l r e a d y p o l a r i s e d vsl.1 i n t o t h e l a l c l re^a ons a t t he c o r -
r o s i o n p o t e n t i a l .
Both the anodic and ca&houic VaJol s lopes 2oi- tho no r -
mal p o l a r i z a t i o n curves and f o r the chemical ly determined
p o l a r i z a t i o n curves a re ^iven in f a b l e 3. :iote t h a t t^.e
cat i iodic va lues ob ta ined oy Ul rcc t polarisa 'Gion a re s i g n i -
f i c a n t l y h igher than the 1X5 - x i l i i v o l t s ei-pocted Tor the
hydrogen e v o l u t i o n r e a c t i o n , while; the va lues ob ta ined by
cn e p i c a l a n a l y s i s a r e not only c l o s e r bo the expec ted , bu t
a re aud i more r e p r o d u c i b l e . £he va lues obta ined by d i r e c t
p o l a r i z a t i o n are probably J n i l uencad . s i g n i f i c a n t l y by con-
c e n t r a t i o n p o l a r i z a t i o n in these r e g i o n s of high impressed
ca thod ic c u r r e n t s . The anodic va lues obtained by both
chemical and e l e c t rochecdca 1 no la r i f ca t i on •methods agree
•with each o the r very wel l in both the i n h i b i t e d ana in
t h e u n i n h i b i t e d sys tems. yince the anodic r e a c t i o n i s
t h e dissolving oi" fcJr i ron ix-seli", so t h a t t h e r e can be
no c o n c e n t r a t i o n s changes, i t i s not so l i k e l y t h a t con-
c e n t r a t i o n p o l a r i s a t i o n would be ev iden t even a t high
c u r r e n t s .
TABLE 3
SUMMARY OF TAFEL SlXJPiiS OF POLKRmTION CORVES
(2. OK rfCl, 30 C)
ZvLu ±'il £h& *.} r f *U,
No I n h i b i t o r , Direct P o l a r i z a t i o n 0.132 0.133
No i n h i b i t o r , Chemically Determined P a r t i a l Currents 0.131 0.125
20 ppni I n h i b i t o r , Direct P o l a r i z a t i o n 0.203 0.147
20 ppm I n h i b i t o r , Chem:JCally Determined P a r t i a l Currents 0.199 0.123
Inhibitor i s n-hexadecyl pyridinium c h l o r i d e
in regard to i n h i b i t o r behavior , ther^ i s qu i t e c l e a r l y
a s t rong e f f e c t on the anodic r eac t ion (Tafel slope 131 rav
uninhib i ted t o 1V9 riv i nh ib i t ed ) , and apparent ly none on the
ca thcdic reaction. , conf-Jrrn5ng the "cathodic s h i f t " In cor ro-
sion p o t e n t i a l s . /.t u r c s s r t , nolar5r.e-ci cn behavior studies
by chemical analysis are being extended In to regions very" near
the r e v e r s i b l e pooei- tio,X« of the r e spcc t lvo .V. l f -ce l l hydro-
gen and iron r e ac t i ons. It iu horjetf t h a t a c a r e f u l a n a l y s i s
of data in these regions wi!3. y i e ld a number fo r the anodic/
cathodic area TC^OZ f o r uninhibi ted and ir>hJh5t.ed systems,
s ince these niiuhers vo'.-ild 1< o n even nor p. di root moa ;;>ure of
the aiiOuic v s . the cat) iodic charac te r of the i n h i b i t o r ad~
so rp t i on.
26
rt /*» \rpy T T r * ; " T / x i y T C j
Quaternary ammonium corpounds are e x c e l l e n t i n h i b i t o r s
of ac id c o r r o s i o n , and seem t o i n f l u e n c e the anodic p a r t i a l
r e a c t i o n more than t h e cafchooio. This behavior i s not
r e a d i l y i n t e r p r e t p b l e in terms of p h y s i c a l v s . chemical
a d s o r p t i o n , s ince these cr. irpounes do not possess the free
e l e c t r o n p a i r normally thought t o provide the bonding f o r
cheraisorpticn. Incree^i n£ br.e hydrocarbon bulk in the
. i nh ib i to r molecule narfcedly i n c r e a s e s the i n h i b i t i o n e f f i -
c iency , *«;h3cb i s be be expec ted . However, -tiodest changes
in molecular s t r u c t u r e bst'/.esn molecules of e s s e n t i a l l y
i d e n t i c a l hydrocarbon conser;t .also r e s u l t in marked changes
i n i n h i b i t i o n e f f i c i e n c y , and t h i s behavior i s not c o n s i s -
t e n t with the pu re ly p h y s i c a l adso rp t ion one would expect
from those .Par rosily charged s p e c i e s . E l ec t rochemica l
measurements a l s o i n d i c a t e a pronounced e f f e c t of the
I n h i b i t o r on the tm odi c h a l f - r e a c t i o n , but very l i t t l e
i f any on the ca thonic ha l f - reac bion• In s h o r t , a l l the
evidence obta ined t o dote 'v i th t he se eoi.npcundn ind icate
e i t h e r t h a t t h e y are chenisorfcirig" (but or t h a t die
g e n e r a l l y • ccented evidences of ehenfeorption and the
chetnieorption theory cu co r ros ion i n h i b i t ! o r : need a ewe
nodi f ie,s t i on.
27
- Te A p v> >^ "rn?? c, i iAO 1 t : ? ; w<
• ' o . , J . i r f"-; c:Vi; •• ;;r.r , ""err"nirm. P ; , * A. <<£ <«,£.• U.~i~ <W- vA »v* -. •-JI " Wi' - - -H * *
1 c .
#n rv ?~32 <195°;
F* "ockernMiii anc' A,C• »-'akridest Fnd» sag. Chem»> jjt# r 90 / -i n * 1 54 > •
!,.ih-. •"• r TVrl T5r Uj, €H»4J * — •? » ~Jti<: 3 * t v i li # 4 * < «xU >£ »> j •*•-' • * I 4r *'
r%~rr -'S Ifl 'si <'h. # I |tV,jut7irj 3, ^ ' / \ A* y „•' *••' *
4. Mannj C.A., Trans ^leetroehem. 3oc,» Jbg, 115 (1936)
5. Machu, Ibid, 22» 133 U W ) .
5. ^ackr is, J/\ -wey, V J. nln?s. and Colloid C!xr.,.f J&, S-7' a ^ J .
7'# «-•-.'.ck<• rniari t •«> •r%.-iiw ..ct.. >-sx: •> : • * »> : ;:> > Jis ?37
f>« K.J, Tfj/sklps, JLIl* "^9 (1963)
28
APPENDIX I
Synthesis of the Quaternary Inhibitors
The Synthesis of Benzyl Pyridinium Chloride
This synthesis, the only one found in the literature,
required taking benzyl chloride and pyridine in equal amounts
and refluxing in an alcoholic media, for ten hours at 90 C.
The liquid is evaporated, leaving benzyl pyridinium chloride,
A preliminary experiment was tried to see what the rate
of formation of benzyl pyridinium chloride (PPCl) was. After
the pyridine was distilled, it was mixed with benzyl chloride
and after about one hour crystals formed. Recrystallization
was tried with various solvents. It was Insoluble in hexane,
ether, and acetone, and extremely soluble in water and all
alcohols.
The first try to make a large amount of the compound in-
volved using hexane as a solvent* Thirty-eight and nine-tenths
grama pyridine were mixed with sixty-two grams of benzyl chlo-
ride which was added drop-wise and re fluxed for about one hour.
The odor of pyridine still prevailed. Hecrystallization of
the material from isopropyl alcohol proved unsuccessful.
A second try using isopropyl alcohol as a solvent and re-
fluxing at 130 C for 7*5 hours produced a brownish viscous
.material. After sitting for two weeks, crystals formed and
were filtered. Hecrystallization from ethanol produced oily
29
drops in which crystals did not come out of solution. Anoth-
er try using acetonitrile as a solvent produced crystals more
rapidly.
After close observation it was noticed that the BPC1 was
very deliquescent. Thus ether Mas used to dissolve the im-
purities and keep the BPC1 as a solid. After the impurities
were removed, the compound was quickly placed in a desicator
with sulfuric acid as a dessicant. A typical yield was sev-
enty per cent.
A silver nitrate titration by Fajan's method for chloride
determination shoved 17.3/' chloride which is also the calcu-
lated percentage.
Synthesis of N-Kexadecyl Pyridinium Chloride
Twenty grams of pyridine and sixty grams of N-Hexadecyl
Chloride were refluxed for seven hours at 145 C in no solvent,
A brownish semi-solid with a pyridine residue remained. This
was racry3tailized frem water and isopropyl alcohol to no
avail. The remaining crystals "were rinsed in ether and the
dried ncn-deiquescent crystals were placed in a dessicator.
Fajan*s method failed on this compound whose yield was
50f because the crystals turned the water brown and the end-
point could not be seen. But an infrared analysis showed up
exactly as the standard I'i-fiexadecyl Pyricinium Chloride from
Eastman f?536l.
30
Synthesis of 2-Sthylbenzene PyrirHnium Chloride
Twenty grams of pyridine and 35 grams of 2-chloroethyl-
benzene were mixed in acetonitrile and reflmsed at 130 C
for tan hours. White crystals formed, i-mre filtered„ and
were dried. The melting point was found to be 103 C and
the chloride percentage was 17.1# where the calculated is
16.2/i , iiold was 20 grams.
Synthesis of 3-Propylbenze.no Pyrldiniuin Chloride
Twenty grama of pyridine and 43 grams of 3-chloro-propyl-
ben zene were mixed in acetonitrile and re fluxed for ten hours
at 120 C. After three weeks without crystallization, seeding
was tried with benasyl-pyridinium chloride and 2-echyl-benzene
pydidinium chloride to no avail. The acetonitrile was evap-
orated and two phases appeared. The denser phase (brownish
with a pyridine smell) amounted to 9ml while the lighter
yellow phase had about 60al. Both phases were sent to an IR
analysi s.
