Experimental demonstration of corrosion phenomena: Part II. corrosion phenomena of steel in aqueous...
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Experimental Demonstration of Corrosion Phenomena Part II. Corrosion Phenomena of Steel in Aqueous Media Elsa M. Arce, Roman Ramirez, and Felipe Cortk lnstituto Politecnico National, ESIQIE, Div. ingenieria Metalurgica, Ap. Postal 75-874, Mexico, D.F., Mexico Jorge G. Ibaiiezl Universidad Iberoamericana, Depto. de lng. y C. Quimicas, Prol. Reforma 880, 01210, Mexico, D.F., Mexico Modern applications of steel are innumerabk, from basic construction materials to the fabrication of so~histicated reaction vessels used in highly aggressive environkents. Un- fortunately, corrosion affects steel to the ~ o i n t that it has been estimated that approximately 25% of the world produc- tion of steel is lost due to corrosion (I). In Part I (2), we showed the phenomena of corrosion, passivation and pitting of an iron electrode in aqueous media. In the experiments described below, we use a sample of carbon steel SAE 1065 (or UNS-G-10650 using the Unified Numbering System (3)) with an approximate weight percent composition as follows (4): C 0.60-0.70, M n 0.30-0.60, P (max) 0.040, and S (max) 0.050 (the rest is Fe) to show the effect of aeeressive ions .... (e.g., CI-) and inhihiting ions (e.g., NO?-) upon its corrosion behavior. bv wine the ootentiodvnamic anodic ~olarization technique (2,5,6j. In addition, the effect that ihe C1- con- centration has uDon the time reauired for the initiation of the breakdown the passive filmon the surface of the steel electrode (induction time, T) is put in evidence. Experlrnental A 0.5 M HzSOa stock solution was prepared with deionized water, and three aliauots where taken: (a) with no additives. h) enoueh NaCl was ad& to make a 1.0 M KaCl solution, and (r; I\'~cI u& addednsin h,nndao wnsNaNOlnstomakra0.5M UaNO~solutiun. All reagents were anal>~ieal grade. The experiments were performed in a conventional three-elee- trode (working, WE; auxiliary, AE, and reference, RE) Pyrex cell, with an approximate capacity of 100 mL. The working electrode was a steel 1065rod ($ = 11.1 mm), encap- sulated into an eooxv resin matrix: the exnosed electrode surface . . was mirror-polishedbeforr earh run with sandpaper s6OO and wirh sureersively liner alumina suspensions tdom to 0.0:) rm) and washrd wirh deionized water. The auxiliary electrode wa- a aplral madeof platinum wire, prevrously cleaned hy immersion in hot aqua rrgia tnirrohvdrorhl~rric acid). The reference electrode was a ratu- rated calomel electrode WE), and all the wtentials measured were given with reference to the SCE. Each soluiion was de-aerated with N. before each run. and a Ng atmos~here was maintained inside the eeil durine the wh& exoeriknt. ?he tem~erature was maintained -~~~ . at 15 T. For earh sysrrm thun generated, the corrosion plmntial (E,,,,) was measured at open circuit hetween the WE and the RE from this potential, the potentiodynamie anodic polarization ex- periments were performed for earh system, at a scan rate of 5U m\' s :.The applied potential was controlled with a BAS potentiostat model CV.2". and the obtained rirnal (, vs. E) was plottrd with a BAS X-Y recorder; however, pra>tically any simpier equipment could be used as well. As for the induction time experiments, the 0.5 M Hi301 stoek solution and the cell described above were also used following the same procedure. A potential was then applied to the WE so as passivate it at E = 1.25 V during 10 min. Enough NaCl was then added to different aliquots of the H2SO4 stock solution to prepare Clsolutions with the following concentrations: (a) 5 X M, (b) 1 Presented at the 199th Meeting of the American Chemical Society. Boston. MA. April 22-27. 1990. ' Author to whom correspondence should be addressed. Figure 1. Anodic potentlodynamlc polarization curves of 1065carbon steel in: (a) 0.5 M H.S04. (b) 0.5 M H.SOdl.0 M NaCI, and (c) 0.5 M H2S0,11.0 M NsCII 0.5 M NaN03. X M, and (c) 5 X M; the electrodes were then immersed in each solution, and the current produced at E = 1.25 V was recorded. The time elapsed from here to the onset of the current production is taken as the pitting induction time, 7 (7). Results and Dlscuslon The anodic polarization c we obtained for the 1065 steel electrode in 0.5 M H2SOais shown in Figure la. This c w e shows an active dissolution zone up to a critical point where the current starts decaying drastically due to the formation of a passivating layer that reduces corrosion in a small pas- sive zone (2, 7,8). As the scan is continued, a zone is reached where the current increases due to either the solvent decomposition and/or to the breakdown of the passivating layer and the dissolution of the metallic substrate (transpassive zone) (5). When the C1- ions are added to the system, the passive zone disappears (see Fig. Ib) due to the localized breakdown of the passivating layer (pitting) (2, 7,8). When the Nos- ions are added to the steell0.5 M HzS04/1.0 M NaCl system, the active dissolution zone is followed by a drastic current de- crease, by a small peak and by a wider passive zone (Fig. le). The first two features were explained above, whereas the small peak observed is due to the initiation of pitting by the C1- ions, which is then inhibited by the NO3- ions; the presence of the Nos- induces the repassivation of the steel Volume 68 Number 4 April 1991 351
Transcript of Experimental demonstration of corrosion phenomena: Part II. corrosion phenomena of steel in aqueous...
Experimental Demonstration of Corrosion Phenomena
Part II. Corrosion Phenomena of Steel in Aqueous Media
Elsa M. Arce, Roman Ramirez, and Felipe C o r t k lnstituto Politecnico National, ESIQIE, Div. ingenieria Metalurgica, Ap. Postal 75-874, Mexico, D.F., Mexico
Jorge G. Ibaiiezl Universidad Iberoamericana, Depto. de lng. y C. Quimicas, Prol. Reforma 880, 01210, Mexico, D.F., Mexico
Modern applications of steel are innumerabk, from basic construction materials to the fabrication of so~histicated reaction vessels used in highly aggressive environkents. Un- fortunately, corrosion affects steel to the ~ o i n t that it has been estimated that approximately 25% of the world produc- tion of steel is lost due to corrosion ( I ) . In Part I (2), we showed the phenomena of corrosion, passivation and pitting of an iron electrode in aqueous media. In the experiments described below, we use a sample of carbon steel SAE 1065 (or UNS-G-10650 using the Unified Numbering System (3)) with an approximate weight percent composition as follows (4): C 0.60-0.70, Mn 0.30-0.60, P (max) 0.040, and S (max) 0.050 (the rest is Fe) to show the effect of aeeressive ions .... (e.g., CI-) and inhihiting ions (e.g., NO?-) upon its corrosion behavior. bv wine the ootentiodvnamic anodic ~olarization technique (2,5,6j. In addition, the effect that ihe C1- con- centration has uDon the time reauired for the initiation of the breakdown the passive filmon the surface of the steel electrode (induction time, T ) is put in evidence.
Experlrnental A 0.5 M HzSOa stock solution was prepared with deionized water,
and three aliauots where taken: (a) with no additives. h) enoueh NaCl was ad& to make a 1.0 M KaCl solution, and (r; I \ ' ~ c I u& addednsin h,nndao wnsNaNOlnstomakra0.5M UaNO~solutiun. All reagents were anal>~ieal grade.
The experiments were performed in a conventional three-elee- trode (working, WE; auxiliary, AE, and reference, RE) Pyrex cell, with an approximate capacity of 100 mL.
The working electrode was a steel 1065 rod ($ = 11.1 mm), encap- sulated into an eooxv resin matrix: the exnosed electrode surface . . was mirror-polished beforr earh run with sandpaper s6OO and wirh sureersively liner alumina suspensions tdom t o 0.0:) rm) and washrd wirh deionized water. The auxiliary electrode wa- a aplral madeof platinum wire, prevrously cleaned h y immersion in hot aqua rrgia tnirrohvdrorhl~rric acid). The reference electrode was a ratu- rated calomel electrode W E ) , and all the wtentials measured were given with reference to the SCE. Each soluiion was de-aerated with N. before each run. and a Ng atmos~here was maintained inside the eeil durine the wh& exoeriknt. ?he tem~erature was maintained ~~~~~~~~~~ -~~~ ~~~ . at 15 T. For earh sysrrm thun generated, the corrosion plmntial (E , , , , ) was measured at open circuit hetween the W E and the R E from this potential, the potentiodynamie anodic polarization ex- periments were performed for earh system, at a scan rate of 5U m\' s :.The applied potential was controlled with a BAS potentiostat model CV.2". and the obtained rirnal (, vs. E ) was plottrd with a BAS X-Y recorder; however, pra>tically any simpier equipment could be used as well.
As for the induction time experiments, the 0.5 M Hi301 stoek solution and the cell described above were also used following the same procedure. A potential was then applied to the WE so as passivate it at E = 1.25 V during 10 min. Enough NaCl was then added to different aliquots of the H2SO4 stock solution to prepare Clsolutions with the following concentrations: (a) 5 X M, (b) 1
Presented at the 199th Meeting of the American Chemical Society. Boston. MA. April 22-27. 1990.
' Author to whom correspondence should be addressed.
Figure 1. Anodic potentlodynamlc polarization curves of 1065 carbon steel in: (a) 0.5 M H.S04. (b) 0.5 M H.SOdl.0 M NaCI, and (c) 0.5 M H2S0,11.0 M NsCII 0.5 M NaN03.
X M, and (c) 5 X M; the electrodes were then immersed in each solution, and the current produced at E = 1.25 V was recorded. The time elapsed from here to the onset of the current production is taken as the pitting induction time, 7 (7).
Results and Dlscuslon The anodic polarization c w e obtained for the 1065 steel
electrode in 0.5 M H2SOa is shown in Figure la. This c w e shows an active dissolution zone up to a critical point where the current starts decaying drastically due to the formation of a passivating layer that reduces corrosion in a small pas- sive zone (2, 7,8).
As the scan is continued, a zone is reached where the current increases due to either the solvent decomposition and/or to the breakdown of the passivating layer and the dissolution of the metallic substrate (transpassive zone) (5). When the C1- ions are added to the system, the passive zone disappears (see Fig. Ib) due to the localized breakdown of the passivating layer (pitting) (2, 7,8). When the Nos- ions are added to the steell0.5 M HzS04/1.0 M NaCl system, the active dissolution zone is followed by a drastic current de- crease, by a small peak and by a wider passive zone (Fig. le). The first two features were explained above, whereas the small peak observed is due to the initiation of pitting by the C1- ions, which is then inhibited by the NO3- ions; the presence of the Nos- induces the repassivation of the steel
Volume 68 Number 4 April 1991 351
/.XI@ M ,,/-ixl0-/-" I ly Several shown hy corrosion-related using the anodic phenomena potentiodynamic of steel may polarization he easi-
technique. These experiments can he performed in a 3-h lab session.
Acknowledgment E= 1.25V One of us (JI) acknowledges partial support from PEMEX
and from Project INQ-050 of the Universidad Iheroameri- cana. "
5 10 15 2 0 25 3 0 Literature Clted TIME ( MIN.) 1. J. chem.Educ. SteftJ.Cham.Edue. 1979.56.673-674.
2. Solona. 0:Ibhdoe. J. G.; Olivares, L. J. Cham.Educ. 1991,68,175-177. 3. ~ i l l ~ ~ . C . P. Corrosion Control in the ChamicdPracers Industrie8;McGrav-Hill: New
Figure 2. Potentiastatic ivs. f cuwes (at E = 1.25 V) for 1065 carbon steel in York, 1986: p 97. 0.5 M HzS04 with different CI- concentrations: (a) 5 X M. (b) 1 X M, 4. Norden. R. B. In ChemicolEnginear's Handbook, 5th ad.; Perry, R. H.; Chilton, C. H.,
and (c) 5 X M. Eds.: MeGraw-Hill: New York. 1975;Senion 23, p51.
5. Uhlia, H. H.: Revie, R. W. Corrnrion and Corrosion Control; Wiley: Neu York, 1985: chapters 5 and 6.
6. E. G, and G. princeton AppliedResearch. Appliestio" Notecon. 1,Bosics of corroaian
(7). As for the induction-time experiments, the time re- ~ ~ ~ ~ ~ ~ ~ ~ e n t s : ~ r i n ~ ~ t o ~ , NJ, 1982: p 2.
quired for the onset of the pitting of the passivating layer ( r ) 7. Gaivele. J. R. 1" Passivity ofMetais: FrankenUlal, R. P.: Kruger,J., Eda.: The Elrctro-
chemical Society: Princeton, NJ, 1977; p 285. decreases as the concentration of the aggressive ion increases 8, wrang~en. G. an mrwiuction to corrosion and ~ ~ o t r c t i o n oi M ~ I ~ I Z : chapman and
(Fig. 2). Hall: London, 1985: Chapter 5.
352 Journal of Chemical Education
