Hehaviour of Mild Steel
Indi an Journal of Chemical Technology VoL 6. July 1999, pp. 202-206
The influence of auramine 0 on the corrosi o i~ hehaviour of mild steel
R S Chaudhary* & Santosh Sharma
Department of Chemistry, MD Universi ty. Rohtak L.-l (,(1 1, In L:;.;
,(eceived 22 October 1997: accepted II J ill/ I! / l}()"
Auramine 0 was investigated as inh ibitor fo r th e corrosion of mild steel II I I () M ~olt lti o n of various (sulphuric. hydrochl ori c. perchloric and phosphoric) acids by studying wei ght loss. pol ;] risatio ll curvr, (lilLl using electron spectroscopy for chemical analysis tec hnique. Vari ous corrosion parameters such as Taf,:1 51\ i)' . Cllrrosion rate. heat of adsorption and ac ti vation energy valu es were calcul ated to und erstand th e mechani sm of i llI.: ';i li() I ~. Inh ibi tion effic iency in creased with in crease in co ncentrat ion of the inhibitor and decreased with in crease in temperature. Aurall line 0 was physically adso rbed on th e su rface of mild steel following Langmuir isothermllild ac ted as a mixed inhi bit or.
Mild steel is widely used in a variety of industries distilled water. For weight loss ~xpe riments, especially for structural appli cations. When mild steel rectangular sp ec ;, nen ~ ur SIL.e I.S x 3 cm2 were used, comes in contact with aggressive environment it whereas for the e lectrochemical studies th e specimens corrodes heavily and requires some means to protect had a workin g areJ. of I x I cm 2 with a 4cm long stem it from corrosion. Mild steel may come in contact to make e lectri cal cOll tact. All the specimens were with various acid solutions during che mi cal processes, po li shed success!"c ly with 1/0 , 2/0, 310, and 4/0 acid c leaning. transportation of acid, descaling grades of emery paper and were ther. thoroughly operations and storage of acids. Di ssolution rate of c leaned with .... ,.tler and aceto ne. Immersion tests were mild steel in acids is quite high. During the recent performed with exposure fo r 4 h using 100, 200, 400 years, there has been a trend in industries to add dyes and 800 ppm of auramine 0 in I .OM solution of each to acid solutions, especially where dyes do not acid at 30, 40 and 50°C in an air thermostat, interfere with the use of acid, so as to give it a e lectronicall y maintained within an accuracy of par1icular colour to make it easier for the industry to ±O.SK. Duplicate specimens were exposed for each educate its workers to handle acids carefully. The use condition and the mean mass losses are reported. The of dyes like vi ctori a blue, malachite green, fuchsine, e lectrochemical studies were carried out using methyl violet, ali zarin red S, catechol violet, fast potentiostaUg i. I vanostat PGS 201 T (Radiometer sulphon, acridine orange etc. in acids as inhi bitor has analyti cal, SA, Fr:1I1ce) . T he glass electrochemical cell 6 been reported by some workers t·5 but th eir use for was similar to that described by Greene . A platinum controlling the corrosion of mild steel in acidic e lectrode was used as an auxi li ary e lectrode and all solutions has not been investi gated uptil now. potentials were measured against saturated calomel In th e present work the use of auramine 0 as electrode (SCE) which was connected to the solution inhibitor for mild steel in various acids (H 2S04, HCI, through a Lu ggi n capillary filled with the
HCI04 and H, P04) has been investi gated at different experimental solution. temperatures usin g 100, 200, 400 and 800 ppm concentration of auramine O. Linear p o lar i.;a~io n resistance measurements were carried OUi galvanu_tLi ticall y. The specimen was first Experimental Procedure polarised in cathouic directi on upto a maximum shift Commercial mild steel sheets used for the of 14mV from the r:> pen circuit potential (OCP) value investigati on had the following composition. C-O. I ~ " in steps of ~ .Il V. Aft er cathouic polar.isation, th e Mn-0.2S, Si-0.03, P-O.IO, S-0.02, Ni-O.O I, Cu-O.O I, specimen was again kept at th e OCP fo r about 10 min Cr-O .O I (wI. %). All the chemicals lIsed were of AR and then anodIC pulari s tion was carried out in the grade and the solutions were prepared using double similar manner. Anodic and cathodic Tafel slopes were measureu alter lecording anodic and cathodic polarisations of the specimen lIpto a maximum shift 'For cn rre s p o ntkn c~ of 120mV from OCP. Anodic and cathodic CHAUDHARY & SHARMA: INFLUENCE OF AURAMINE-O ON CORROSION OF MILD STEEL 203
-39or------~
~ Ul 'M HCI,40· C ~ -430 Auromln.O 0- '00 ppm > . x -200ppm E 0-1. 0'-4 H S0 ,40 C -470 2 4 o -400ppm Auromine 0 "0 !J. - 800 ppm o-'OOppm c x- 200 ppm .. -510 0 a.
..,.. -550 .0 ...- Uj -590
' 0.000 -630 L------,~OO-O------,-OOLO-O------~,O~OO~O~O--~
Fig. I b---Cathodic and anodic polarization curves of mild steel in presence of different concentrati on of auramine 0 at 40°C in 1.0 Fig. I a-Cathodic and anodi c polarization curves of mild steel in M hydrochloric acid solution. presence of different concentration of auramine 0 at 40°C in 1.0 M sulphuric acid solution. cI. -439 -459 - 4'4 8 -479 UJ -434 u ;-490'" 1/'1... _454 1 M Hel 01. )40 °C E ;> A,uromlne 0 --5'9 E -474 ~-~9 a 0 - 100 ppm c ~ -494 X - 200 ppm ! -559 o 0-41 .4 0-1,,00 ppm Co a. -679 ~ -534 ~ - 800 ppm ':;-599 o -B.. -554 ~.. -619 Uj -574 Uj -639 -594 -659 -679 '--______..L- ______-'- ______--'- ______-1 614 L------:c,OLO -'--O ----"---"--","'"Oo":o-=-o------,' -=-00:":0=-=0-=-0---' '00 '000 '0000 Curre-nt density, )JA/cm2 Curr.nt den5ity . jJ Ale m2 Flg. I c-Cathodic and anodic polarization curves of mild steel in Fig. Id-Cathodic and anodic polarization curves of mild steel in presence of different concentration of auramine 0 at 40°C in 1.0 presence of different concentration of auramine 0 at 40°C in M perchloric acid solution. I .OM phosphoric acid solution.
polarisation curves were recorded galvanostatically at calculated from weight loss measurements and are 40°C usin g different concentrations of auramine 0 in summari sed in Table I. It is clear from the results that all acids. auramine 0 proved to be a good inhibitor for Surface elemental analysis of the surface of phosphori c acid and sulphuric acid solutions but the corroded specimens in absence and presence of the effi ciency was low for perchloric and hydrochloric inhibitor has been carried out by electron acid. However, inhibition efficiency increased with spectrometer (ESCA 750 Shimadzu Make). Ka X in crease in concentration of auramine 0 and rays from Mg source were used to carry out the decreased with increase in temperatures from 30° to analysis. The samples were anal ysed in an ultra high 50°C. From linear polarisati on resistance data, vacuum (UHV) chamber where pressure of the order corrosion current density I co rr was calculated using of 5x 10- 2 torr was maintained and the instrument was Stern-Geary equation. Inhibition efficiencies and operated at IOkV and 30mA at the time of analysis corrosion rates are calculated and given in Table I. and a temperature of 25°C was maintained. Most The results obtained from the weight loss and ., intense peaks of C, Fe, CI, N were recorded and exact electrochemical polari sation techniques are almost value of the binding energy of each peak was found similar. out from th e ESCA spectra. The complete anodic and cathodic polarisation curves for mild steel in I.OM solution of various acids Results and Discussion in absence and presence of different concentrations of Inhibition effi ciencies of auramine 0 in varIOUS auramine 0 at 40°C are plotted in Fig. la, I b, I c and acid solutions at different concentrations were I d. Similar polari sation curves were obtained at 30° 204 INDIAN J. CHEM. TECHNOL., JULY 1999
Table I-Inhibition efficiency and corrosion rates of mild steel in presence of different concentrations of auramine 0 in 1.0 M solutions of various acids [Exposure time (Weight loss): 4 h] Percentage inhibition Percentage inhibition Percentage inhibition Percentage inhibition efficienc;t H~S04 efficienc;t HCI efficienc;t HCI04 efficienc;t H,P04 Inhibitor Temp., Wt loss Polari- Corro- Wt loss Polari- Corro- W! loss Polari- Corro- W! loss Polari- Corro- conc. O°C method sation sion method sation siQn method sation sion method sation sion ppm resis- rate resis- rate resis- rate resis- rate tance (mpy) tance (mpy) tance (mpy) tance (mpy) method method method method None 30 t 205.8 178.3 86.8 253.9 40 h487.5 204.2 159.6 482.5 50 1929.6 357.4 252.4 852.6 100 30 62 .6 62.8 448.5 43.8 49.9 89.2 13.6 14.0 74.6 83.6 84.9 38.2 200 30 73.6 75 .5 295.3 48.8 55 .6 79.3 24.4 22 .0 67.7 89.4 88.5 29.0 400 30 86.9 84.9 181.9 55.0 59.3 72.7 56.3 57.6 36.8 92.5 90.7 23.4 800 30 92.4 91.6 100.5 59.5 63 .2 65.6 69.7 70.3 25.7 95.1 93 .4 16.7 100 40 58.4 56.2 650.4 33.4 31.8 148.8 10.2 8.8 145.4 77.5 74.1 124.6 200 40 67.6 69.3 455.4 39.6 38.8 132.3 16.3 20.2 127.3 84.6 83.1 81.1 400 40 83.2 84.6 228.4 45 .0 45.8 117.2 39.3 47.2 84.1 88.7 86.5 64.9 800 40 89.2 89.4 156.8 50.8 49.1 108.4 64.2 64.7 56.2 92.9 89.5 49.6 100 50 52.8 51.9 927.2 26.6 28.2 256.2 2.5 2.0 247.3 70.2 71.4 243.5 200 50 61.6 65.0 674.6 32.6 34.9 232.5 10.6 11.1 224.3 78.4 79.8 172.2 400 50 78 .5 79.4 396.3 37.9 40.6 212.0 26.4 30.1 176.2 83.5 83.2 142.5 800 50 84.7 86.7 254.8 43.1 45.8 193.5 56.5 56.7 109.1 86.6 86.4 115.4
Table 2-Heat of adsorption and activation energy values for mild acids. Plots of log 8/1-8 versus log C, where 0 is the steel in presence of au ramine 0 in various acid solutions fractional coverage of the surface with inhibitor and C Conc of HCI is the concentration of the inhibitor, for mild steel in auramine 0 , presence of auramine 0 are linear (Fig. 2a-2d). ppm Therefore, Langmuir adsorption isotherm equation is Heat of absorption Mf (kcal) followed by auramine 0 at all the three experimental temperatures suggesting that the inhibitor molecules 100 3.9 2.9 7.4 6.7 200 5.1 3.3 8.7 7.9 are adsorbed over metal surface forming a barrier 400 5.5 4.1 9.9 8.5 which prevents the contact of metal with electrolyte. 800 7.5 4.5 10.8 10.3 From the slope of straight lines obtained from the Activation energy Ea (kcal) plots of log 8/1 -8 versus liT, values of MI were calculated (Table 2) using the equation: Nil 4.5 6.2 7.1 12.5 100 7.9 8.0 9.1 8 f1H 15.6 log --= log! AC) - ---- 200 8.3 8.4 11.4 16.1 1-8 ~ 2.303RT 400 8.7 8.9 13.0 17.4 800 9.9 9.8 13 .7 20.1 where A is a constant independent of temperature and dependent on the characteristics of the system and Tis the temperature of the system. Low values of MI of and SO°e. It is obvious from the polarisation curves auramine 0 suggest that it was physically absorbed on that both anodic as well as cathodic curves shift the mild steel surface in each acid investigated. towards lower current density values in presence of Activation energy, Ea, values for corrosion reaction the inhibitor indicating that the inhibitor acts in such a were calculated from the slopes of the plot of log Icorr manner that both anodic as well as cathodic reactions versus liT using the equation: are influenced by it simultaneously almost to the same E. = 2.303 x 1.987 [(log Ic orr)/( 1/7)] extent suggesting it a mixed inhibitor in all the acids and are given in Table 2. Values of Ea for the investigated. inhibited systems were higher than those of the Various adsorption isotherm equations, namely uninhibited system and increased with increase in those of Tempkin, Langmuir and Freundlich, were concentration of auramine O . applied to th e inhibitor data fo r auramine 0 in all CHAUDHARY & SHARMA: INFLUENCE OF AURAMINE-O ON CORROSION OF MILD STEEL 205
1·4 a c 0·4
~ '·0 I ...... Aura.,i"e 0 CD 0.6 01 0- so·c - 0.2 0 A -4 o·c • - 50·C 0·2 <2> ,.!...... Auramin. 0 -4.0 -3.0 - 2.0 -1.0 <2> -0.8 0 30°C log e mol/! C7I 0 A 40·C so·c 0·1 • b -1·4
.., -0.1 CZI .!. - 4.0 -3.0 - 2·0 -1,0 "-() -0·3 tog e,motlt Auro(TllneO C7I 0 0- 30°C 1. 6' cl -0·5 "-40° e • - 500 e
<2> 1' 0 -4.0 -3·0 -2.0 I loge molll ~ Aura mine 0 Fig. 2a & b--Langmuir plots for adsorption of auramine 0 on the C7I 0 0 30°C surface o(mild steel in l.OM H S04 and HCl respectively. 2 0·4 A 40"C 5 O·C Auramine 0 has the molecular structure, •
-4·0 - 3·0 -2·0 -1·0 tog e.mol/l
Fig. 2c & d--Langmuir plots for adsorption of auramine 0 on the
surface of mild steel in I.OM HCI04 and H)P04 respectively.
When added in acids, molecule will be pn)tonated as it is in the least sterically hindered part of the as shown below: molecule. Elemental analysis of the mild steel surface in absence and presence of auramine 0 for observing various peaks of C, N, CI and Fe was carried out by ESCA technique. Observed values of binding energy for C, N, CI and Fe from ESCA spectra have been 1 recorded in Table 2. It was observed that in addition to C and Fe peaks observed in blank acid solutions, peaks for nitrogen and chlorine were also observed on The imino nitrogen in this structure is likely to the surface of mild steel exposed to inhibited acid have higher electron density in comparison to other solutions. It confirms that the adsorption of two nitrogen atoms present in the molecule. The point auramine 0 molecules has occurred over metal of adsorption in this molecule will be imino nitrogen surface which helps in protecting it against corrosion. 206 IND IAN J. CHEM . TECHNOL., JULY 1999
Tahl e 3-Bindi ng energies of the element s present on mild steel surface in absence and presence of aura min e 0 in i .O M soluti ons of vari ous acids Observed valu e eV
H2SO4 HCI HclO4 H3P0 4 Elements Peak Literatu re Blank Inhi bit ed Blank Inh ib ited Bl ank Inh ibited Bian k Inhi bited present recorded valu e eV
C 1S 112 287 286.7 286.9 286.6 286. 1 286.6 286.4 286.8 286.0 N 151/2 402 Abse nt 401.4 Absent 40 1.9 Absent 40 1. 9 Absent 40 1.0 CI 2P .v2 199 Absent 198.8 198.6 197.2 198.5 197.9 Absent 198.5 Fe 2Q312 710 708.7 708.1 708.7 708.4 708.8 709.2 709.5 709.4
Conclusions (iv) Acti vati on energy for the corrosion reaction of (i) Auramine 0 showed maxImum inhibition inhibited syste m was always hi gher than the efficiency in phosphoric acid (95.1 %) while in uninhibited syste m. hydrochl oric acid solution it was the least (59.5%). (v) Resu lt s of ESCA study supplement the findings However, inhibition effi ciency increased with that Juramine 0 is adsorbed on mild steel sUIface in inc rease III concentrati on of auramine 0 and all acids in vesti gated . decreased with in crease in temperature. References I Ta lati JD & Gand hi OK. J Electrochern Soc. 32 (1983) 380. 2 Talati J 0 & Oaraji JM . J Electrochem Soc. 35 (1986) 175 . (ii ) Auramine 0 acted as a mixed inhibitor In all 3 Ta lati J 0 & O ~ r aj i JM . .I Indian Chern Soc LXV (1986) 94. acids in vesti gated. 4 Gupt a P. Chaudhary RS. Namboodhiri TKG, Prakas h B & Prasad BB . Corrosioll , 40 (1984) 33. (iii) Adsorption of auri1 mtne 0 obeyed Langmuir 5 Ouhey R S, Ph.D. Th esis, Banaras Hindu Uni versit y, adsorption isotherm equation in all acids and was Vara nasi. 1990. 6 Greene NO. Expl'I'illl eliw/ Electrode Kill etics (Renssel eaer phys ical in nature. Po lyt echnic In stitute, Troy, New York ), 1962.