rfcPtl r a q i J o u r n a l o f C h e m i c a l a n d P e t r o l e u m E n g i n e e r i n gV o l . 8 N o . 1 ( f t 4 a r c h 2 0 0 7 ) 4 7 - 5 0 Corrosion Inhibition of Low Carbon Steel in Different HCI Concentrations by Phenythiourea A p r a e l S , Y a r o ' , N a s h w a n A . R a s h e d ' ^ , A n d A h m e d S . A b d u l - H a s s : r n ^ ' C h t q i c o t L a g . n e " L : u D . p a n . - ! . a t t , g . u J L a s t a , $ i , g - t n i v ' r s . ^ o J B n S | / " J - h . t l C h ? " t i c a t S t h l p , C e n e t - I t i a r t t a l h a L 5 y a r J U ' t . ' I l , r l Abstract Phentlthio tea (PHTU),'|as te\ted as inhibitar for the carasion af la\r carban stlcl ,t dilletent HCI dcid canccntration bf nast loss,and palari:ation neasuretrents .it \|as faund that (PHTU) i! d gao!1 inhibitar fat ttrc canosion af loh, carbon steel in l,3,and 5N HCI satutian ,ahd tu inhibitian e[Iciency (0) incrcsscs \9ith its cancentrction and a oins dpproindtely 97% at lg/l .polatization curws indicate that (PHTU) dcts ds an dno.lic i,pe inhibilor the irhibitot wos atlsorbed on the |ae carban steel slltlace according to the Langnrir adsotpti.)n isatherm nodel. Results shov, thdt the rcte af camsion aflaw catbotl steel in.reased rrith incrcd!lng tentwtutu e orer tte trtlse 30-64'C, both in the presence af inhibitat and its absence .it uasfound atsa that the hrhibitikg qfect afllc inhibitot is genetuUr acid concentration independent. /(sJralr/s: phenylthiourea, lowcarbon steel, corrosion inhibition. Introduction To control the corrosion ofmelals in several industrial processes, acjd inhjbitors are usually used. M€tals are exposed to lhe action of acids i! many ways, and for many diff€rent reasons. The exposures can be most severe bu! in many cases, the corrosion can be controlled by nicass of inhibitors. Processes jn lvhich acids play a very impo11ant part arer Acids pickling, industrial acid c l e a n i n g a n d o i l w e l l a c i d i z i n g l l . M o s t o f r h e w e l l - known acid inhibitors are organic compounds containing nitrogen (N), such as amine and hetrocyclic compounds, besides sulphur and oxygen. The influence of fiese organic inhibitors on the c o r r o s i o n o f s l e e l i n a c i d i c s o l u t ; o n s r a s o c € n investigated by several workers [2-4].the existing data show, that most organic inhibitor used, act by adsorption o n l h e n r e t a l s u f a c e . d i e s e l e c t i o n o f a s u i t a b l e i n h i b i t o r fbr a ce(ain process depends on many faciors; such as: iis chemical structural, its concentraiion, the naru.e of metal used and $e type ofacid used. The ainl of this study is to investigate the fol€ played b ) p h e n ) h f i o L r c a a s c o u o s i o n i r h i b l o r o n r h e c o r r o . i o n i n h i b i t i o n o f l o l v c a r b o n s t e e l i n l , 3 , a n d 5 N H C I a c i d Experimental Work Gravlmetric measurements The experiments were carried oui in solutions of u n i n h i b i t e d 1 , 3 , & 5 N H C I a c i d s o l u t i o n o n l o w c a r o o n s t e e l c o n t a i n i n g 0 . 0 4 1 % C , 0 . 3 % M g , 0 . 0 5 % phosphorus,o.007% S, remaindeP/o iron. Specimens jn $ e f o r m c o u p o n s w i t h d i D r e n s i o n s o f ( 7 8 9 x 1 . 5 ) c m 2 a n d a thickness of 0.09 cm were used for mass loss measurements studies. They were poiished wilh emery p a p e r o f g m d n u m b € r s 2 2 0 , 3 2 0 , 4 0 0 a n d 6 0 0 . c a c h r u n w a s c a r r i e d o u t i n a g l a s s v e s s e l c o n t a i n i n g l 0 0 0 c m r t e s t s o l u ' i o n . a c l e r n $ e i 8 h e d l o $ c J r b o i y e e l s p c c i 1 ' c l u . . c o n r p l e t c l y i m m e r s e d i n I , 3 , & 5 N H C l a c i d a t 3 0 , 4 0 , 5 0 , & 6 0 ' C . A f t e r 2 h o u r s o f i m m e r s i o n i n 1 , 3 , & 5 N u n i n h i b i t e d l l c l a c i d , t h e s p € c i m e n w a s d r a w n . R i n s e d I J C P E V o l . B N o . 1 ( l \ r l a r c h 2 0 0 7 ) 4 7 Ca asian Inhibitian Low Carbon Steel in ent HCI Cancentratians by Phe vlthiourca with distilled water, washed wilh ethanol& acetone' dficd& weishted. The mass loss was used to calcLrlate ihe corrosion rate in sranls per meter square per dav (gmd)' Polarization measurements Cylindrical electrode (l 96cm outside dianreter and widih of 0.5cm) = 3.13 cm'? area was prepared from investigated carbon sleel. Sanrples were abraded in t . n " - i . " . a . t r u n r i n g r " p w l e r L r s i n g e m e r y p a p c r o f c r r a n u r n l , c r . 2 ? 0 , 3 2 0 , a 0 0 , n d 6 0 0 L h c n $ a s ' r e d $ i l l r iLrnning tap water followed by distilled water, dried with clcon thsue. innrersed in acetone and benzene, kept nr a d e e i c a l o r o v e r s i l i c i g e l b e d L r n l i l u s e T h e c o n c e n t r a , i o n r a n g e o f i n h i b i r o r u s e d w r " ( 0 l 0 . ? 5 . c n d I g l ) . 1 h e s l l | a i . s * " t c c . r r i e d o u t p o l e n l i o - d r n a n i c a l r y i i n a r h e r m o s r a l e d e l e c l r i c a l l i c c e l l P l a r i n ' r m t l i t * u , " s . a u " a . o r n t . r _ e l e c r r o d c L c E r r n d a s a l J r a l e d calomel electrode as a refercnce electrode (SCE) The laler was connected through a luggins capillary to the cell. The wolking eleclrode (WE) was immersed in a test solution .The potentiodynamic current_potentlal curves were recorded by changing dle electrodc polenllal m i l u . l h l r o m ' 8 0 0 l o - 1 0 0 - r V r S C L r ' A l l e \ p e r i r e n s u c r c c a i r i c . t o r r i 1 l l e . h l ) p r e p r r c d s o l , r t r o n : n ( o n r l a l l temperanrrcs 130,40, 50r and 60oC. Results and Discussion l/ass loss measurements Table I collects the vahles of corrosion rate obtalneo from nlass loss measurements for diffelen! temperalures in diffefent HCI acid concentrations. Table I sbows that corrosion rate of carbon steel is firnction of both the LemDeratufe &acid concentratior .This nreans tha! fol ( c r l d i r l l e l n p c l r r L r e o l a L i d L o n c e n l r d t l o n L o - _ o s i o n r a l e i r - r e . b e s d s I h e c . i d c o n c e n l r r L i o l o r l e n p e r d t u r c increases respecilvelY. To elucidate or deiermine the activation energies ofthe coffosion pfocess, nass ]oss measuements *ere prefomed al various temperatures ill the at'sence 0r i r i b i t o r u s e d . I I L a ' b e e n I e p o r l . d ( L . r ' f o r i r o n & s l e e l i n s c i d l l ) e l o : d r i r h m o f I ' c c o r r o ' i o n r j c o f s L e c l C R c a n b e ieiresentea as a straight line funclion of(l/T) (Arrhenius F t ^ o c R = - L a B ( l ) 2 . ] R T Where E is the activation energy, R, is the unjversal sas constan! and B is a constant The variation in i " " r . i , n l n " r . " - * i " " ' " r e o r c . r r b o n s r e e l i n l l a n d 5 N H i l a c i d ' o l u r ' o n . ; r t h e a l ' s e n c c o l ' n h i b i r o r ' \ i r r i""lp-*t oi tt e absolute temperature! is given in Fig- r rt" "utculut"a value of (E), shows that incrcas;ng of acid concentration fron IN to 5 N was associated wilh a decrease in activation energy ftom 16 to 12 5 Kcal/mol r e s p e c t i v e l y t h r o u g h 1 3 7 K c a l / n r o l i n 3 N H C I a c i d Several values given in lhe liierature for activation enersv of carbon steel in HCI solutions, ranging fronr l l 8 ] o 2 1 . 0 K c d l r n o l i s l , $ i r h m a j o r i r ) s r o u p e d a : ? \ l t - ' 1 4 . 5 K c a l / m o l e . Y a r o t 6 l o b t a i n e d a v a l u e o f : : ] Kcal/mole fo[ the corosion of carbon sleel in I\ :i: acid soluiion. Electrochemical measurements Potentiodwamic anodic and cathodic po::-_=' s c a n s w e r e ; a r r i e d o u t a t 3 0 , 4 0 , 5 0 , a n d 6 0 ' C - : and 5N HCI with different concentralioDs of i: - Anodic and cathodic polarization cLlrves in abss':: i n r h c p - e s e n c e o f i n \ i b i l o r n t d i f f e r e n l c o n . e - - - E o a f t e r i m m e r , i o n i n I , l , d n d 5 N H C I a c i d ( - ' t 3 0 " C a r e 5 r o $ n i n F i 8 2 ' d a s a l r n p l e ' _ : n t Dolarizalion !unes rL 40, 50 ard 60'C 'l diiTerti:' L . . inhibitor concentralion immersed in 1, 3, and 5 N are not sholvn here, but they were used to find coroslon parameters i."", R", and Rc) l! can be seen from Figures 2-4, thai in the prcsence ol r n h i b i l o r . r h c ( u r \ e " a r e , h i f t e d t o l o q e r c r r r e . ] l r e g i o s showina the inhibition tendencv of (PHTU) The values of varLus electrochemical co osion parameters are summarized in Table 2. The E."" values were generally shifted pronounsly in the pres;;e of inhibilor to the posilive direction' These obs;rvations show clearly that the inhibition ofcorrosion is under anodic control (i.e, polarization occur's on the a n o d i c & t h e E " , s h i f i e d t o t h e o p e n c i r c r ' r i l o f t h e cathode) I7l. rhc coriosion cuffent densitics and Tafcl slopcs wefc estimated by BETACRUNCH program developed .by G r e e n a r d C a n d i [ 8 ] o n l h e a s " u n p L i o . 1 r L a - l h c c o r f o ' r 0 n r e a c r o n i q t o m p l e r e l y u r d e r a c t : v J l i o n c o n l r o l a n d i ' r o t complicated with IR drop or mass transfer' lnhibition "ir,"i"n"y *ut then calculaled using the mathematical a _ l I t c a r n n I " \' h.,u, ) (2) Where I."" (ln) and l.""(un) are the corrosive current wilh and without inhibitor receptively Table 2 sbows that an increase in inhibition in inhibitor concentration is resulted in increased inhibition emciency, i! is evident from the results that th€ i*" values considerably decreased in the presence ofinhibitor and that the maximum decrease in ic"" coincides with the maximum concentration of inhibitor [9] the inhibiior s r u d i e d p e r r o r m e d e \ L e l l e l r l v ( 9 0 5 ' o i n h i b ; r i o n e f f i ( i e n L y " L l g U a q i n h i b i l o r o l l h e c o ' r o s i ^ n o f l o w carbon steel in lN HCI 4 8 IJCPE Vol.B No.1 (l\,'larch 2007) : h a . 2 6 {cl , 3 , I.J), L a l rhe i o n i o n t h e t h e by i o n t h e i o n ' ( 2 ) Surfac€ coverage (g) values have been evaluated for different concertration of (PHTU) under study from corrosion rates in uninhibned and inhibited solutions using Eq. 2. The Langmuir adsorption isotherm €xpressed KC ':i: cu.dnot : .' . i ! u 1 + K C c t ^ E K Tchp.tohtre,"C 30'C:5N HCI 9 N i l 7 i 7 . l l l 0 0 l g i n h . t 2 5 0 t I I 0.75ginh 84.22 1 2 l g i n h . 7 0 6 9 4 0 ' C r l N H C I t 3 N i l 1 0 1 3 . 8 9 1 4 0 . l C i n h , 6 5 . 9 8 1 5 0 . 7 5 e i n h . 5 0 . 1 9 1 6 l g i r h 4 2 . 9 3 4ooc:3NtlCl 1 7 N i t 1 2 1 1 . 3 3 1 8 0 . l g i o h 1 1 1 : 1 4 1 9 0 7 5 e i n h 8 5 6 5 2 0 I I i n h 6 1 0 3 40'C:5N tlCl 2 t N i l 3 1 7 8 . 3 6 22 0.lg ioh, 399,23 2 3 0 7 5 g i n h . 2 8 9 9 24 lginh 229.39 5 0 0 c r N u c l 2 5 N i t 1 6 0 1 , 0 7 2 6 o . l g n n r 1 1 1 7 1 2 7 0 7 j g i r . 6 4 8 4 2 8 l g i r h . 5 8 . 1 7 50'C:3N flCl 2 9 N i t 6 1 9 9 . 2 8 3 0 0 . l g i n h , 9 0 3 . 8 9 3 l 0 . 7 5 9 i n f i . 5 7 6 1 5 32 Ig inh. 319 50'C:5N IlCl N i l 0 . 1 9 i n | . 0.7ts i,rh l g i n h . J t i 3 . 1 1 t ! r i : : t 2 : 5 : i _ _ s i r ! { 0 5 l 1 i _ t ! ! ! _ 1 2 . 1 . 1 4 i 5 t t : : : 5 3 . 0 8 5 4 | l N i l 4 7 . 1 7 6 t 7 t 9 3 6 l 7 3 . 6 8 8 3 . 6 7 9 5 . 1 4 44.28 52.51 94.84 7 0 9 5 7 1 . 5 5 N i t 3 9 . 1 4 4 3 0 4 9 0 8 40.82 41 t9 929 48.73 56.89 94.4 7 0 . 9 5 7 1 5 5 N i t t 0 l 4 ? I I 8 . 8 3 8 7 4 3 88.74 99.08 90 87 85.9 92.6 92.78 46.14 41.54 Nil 43.57 4928 93 n2 4 1 . 1 4 4 9 . 1 6 9 5 t 6 4822 56.16 96.32 95.91 97.99 Nil 46.16 4847 85.41 46.49 54.92 90 7 43.64 46.32 93.88 l 0 , l 6 7 1 0 5 8 9 N i l 5 2 2 1 5 2 1 1 7 9 7 4 8 . ? t 5 3 9 5 8 4 2 4 9 . 6 2 5 1 . 8 5 8 8 . 1 6 Where K is the equilibdum consiant for the adsorption isoth€rm process, C ;s the inhibiror concentration (91) a n d e i . r h e s | . f f a c e c o ! e r a g e . R e d r r a n g i n g E q J : (4) It was found dut Fig. 5 (plots of C/6 vs. C) for phenylthiourea inhibitor gives srraight Iines with slope, praclically equal to unity, indicatiDg rhar the adsorption ofPHTU undef consideration on carbon steel in t, 3, and 5 N I - l C l a c i d s o l u r i o n s i n r e - f a c e o b e ) . t . , n g f l u r s adsorption isorherm. lt is important to mention here that the same behavior was obtained at 40, 50, and 60.C. The deviation of 1he slope fiom unity is artributed to the difference in tbe rate of interaction betwecn tbe adsorbed species on d1e metal surface. From the intercept ofthe straiSht lines on the C/0 axis, K vahres were calculared. Table 3 shows the eqLrilibrium constant ibr Langmuif lype adsorption ofPHfU inhibito. in 1N HCl acid solution at different tenrperature Table I effect oftemperature and HCI acid concentration on lbe corosion rate (g/m'zday) ofcarbon steel 40"cl 0 . c 50"c I N 3 N 5N 3 9 . 3 5 6 0 2 . 5 5 4 5 6 . 1 7 1 9 0 5 . 4 6 3990.249 9 9 8 7 . r 7 2i22,95 t 5 7 6 . 4 r | l 8 2 4 2 t 5 1 . 8 2 2 7 9 . 8 1 t 7 7 . 8 2 7 4 t . 3 1 t3t8.25 2454.11 l l 34 3 5 36 J 7 3 8 l 9 4 0 Table 2 Conosion Current density, Ba, 0c and Efl values obtained for Low Carbon Steel in differenr acro concentrations in absence &presence ofPHTU 6 0 ' C : 1 N f l c l Nit 2594.68 0 . l g i n n . 1 9 9 . 1 5 0.759inh. 109.24 I g i n h . 9 2 3 52 62 53.05 63.83 74 64 3 3 . 4 t 3 4 0 9 43.01 49.69 N i l 92 31 9 5 7 8a;: c,,,r,,a, ,.|;,, .f,U ,,f1" trJI % lo,c lN flcl I N i l 2 0 l g i n n . 3 07tg inh. 4 r 8 i n h . 30.cr3N HCI 5 N i l 6 0 lg infi. 7 0 7 5 9 i n h . 8 l g i n h . 60'C:3N HCI , 1 1 N i t t 9 9 6 5 l 4 2 0 l C i n h . 1 0 8 8 . 5 8 4 3 0 7 5 g i o h , 8 7 6 . 0 4 44 lC inh. 527 600c 5N HCI 4 l N i t t 0 4 5 4 . 9 8 , 1 2 0 . l g i n h 1 8 4 0 . 7 1 ,11 0 75Bnrh. 1622.14 4 4 l g i n h 1 3 5 4 . 1 5 6 7 5 1 6 9 . 1 1 N i l 3 5 | I 3 t . . 1 3 8 1 . 8 4 4 6 4 3 5 r . 6 1 8 5 l 9 t 8 . t 8 4 2 , 9 2 9 t 2 t 7 8 . s 7 7 9 1 3 N i l 4 7 . 5 8 , 1 8 . r 7 7 7 . 4 8 61 78 71.81 82.J9 4 8 . 1 9 4 9 t ? 8 , 1 4 8 I t 5 . 7 1 2 r . l 9 t 7 . 2 2 t 4 . 9 3 6 4 r . 8 9 9 1 5 5 5 t . 4 6 N i l 93.2 94,54 95 21 N i l 85.73 9 t 9 8 9 2 1 5 5 5 . 7 3 6 1 9 l 4 0 8 3 5 0 8 5 44 94 53.29 46.91 65.56 4 9 . 2 5 7 8 4 7 6 6 5 1 . 2 5 50 82 34.02 42.47 46.62 U C P E V o l . B N o . 1 ( M a r c h 2 0 0 7 ) 4 9 Carras io)1 I nhibit iott af Lo|| Cafto" Steet i' Differcnt HClConcentt dttans ' I a b l e I E q u i l i b r i u m C o n s l a n t l o r A d s o r y l i o n o f t h e P H T U i n h i b i l o r solLrtion at Difierenl Temperatures Langmuir TYPe i n l N t l c l a c r d 3 0 4 0 5 0 6 0 2 9 8 3 , 0 4 3 1 0 3 1 6 J 2 2 ( 1 / T ) x l o " K " I r r . I A r r h c n l u s p o l l o l l o J c o l - o ' l o n r " t e s r d r r o ) v s ' . . i p * , ̂ i " i " r , * 1 " " " " l i t d ' r f e r c n L l l c l r ( i d c o r r c Fig.4 PolarizatioD curves oflow carbon steel in 5N HCI "i"t"i',i"g Jiii.** i"Libitor concentration at 30oC' '- _ rq cdrbof f r t . 5 L a n a n r r i r a d , o r p l i o r i ' o l h e r n o ' r H I u l r r ' ^ ^ . i , r - " - i n d i l T . ' . n ' n o - n . t i r y o f H C l d c i d s o l L l o r d r { u 1 t @ g 3 8 3 4 t e g 3 1 7 5 ( 1 9 9 0 ) . M . A . Q u r a i s k i , C o o s S c r ' ' € Fis.3 Polarizalion curves oflow carbon steel in 3N sci """i"i"i"g ain"*", inhibitor concentration at 30"c References L G . G e o r g e , C o r r o s i o n T a x c s , ( 1 9 7 4 ) 2 . J . M . S y k c r , B r ' c o r [ o s J 2 5 . 3 . M . A j m a l , A S . M i d e e n , l n h i b L t o r , N A C E , l l o L r s t o L r ' Iri!r. 2 Polarization cuNes oflow carbon sleel in lN HCI ''?oirtoi"ing aifi","* i"libilor concentntion at 30'C . . ' n i r i i l l l l i " t . * , o ' \ c i . r r 8 ' | 1 r o o s ' i'::h*"li;:lt o l;:l'f"',lx:l"J.Li '"i "\lJ'.', 1; r 'ii"lLlll, M, M.sc rhesis, univeLsitv or Baghdad ,.f.ll3];*, *o R. candi, Material Perromrance' rulv n.lSlrt]"r, ", M.sc rhesis Irniversitv or Bashda' ( 1 9 8 8 ) . 5 0 I J C P E V o l . B N o . 1 ( [ , a r c h 2 0 0 7 )