THE HARTFORD GRADUATE CENTER SCHOOL OF ENGINEERING AND SCIENCE SPRING 1996 36431 CORROSION INSTRUCTOR: E. GUTIERREZ-MIRAVETE DAY: TUESDAY 5:30-8:30 P.M. ernesto@hgc.edu (860) 548-2464 COURSE OUTLINE REV. 4/4/96 -------------- DATE SESSION TOPIC READING 1/9 S01 INTRODUCTION 1/16 S02 OXIDATION I: THERMODYNAMICS & KINETICS CH. 1 1/23 S03 OXIDATION II: NATURE OF OXIDES; ALLOYS CH. 1 1/30 S04 AQUEOUS CORROSION I: THERMODYNAMICS CH. 2 2/6 S05 AQUEOUS CORROSION II: ELECTRODE KINETICS CH. 2 2/13 S06 AQUEOUS CORROSION III: CORROSION KINETICS CH. 2 2/20 S07 AQUEOUS CORROSION IV: ALLOYS; PASSIVITY CH. 2 2/27 S08 EXAM # 1 3/5 S09 PROTECTION OF METALS I CATHODIC AND ANODIC PROTECTION CH. 3 3/12 S10 PROTECTION OF METALS II INHIBITION; COATINGS CH. 3 3/19 S11 CORROSION FAILURES I LOCALIZED CORROSION CH. 4 3/26 S12 CORROSION FAILURES II STRESS CORROSION CRACKING (SCC) CH. 4 EXAM # 2 (TAKE HOME) 4/2 S13 CASE STUDY I STRESS CORROSION CRACKING (SCC) IN STAINLESS STEELS, INCONEL AND ALUMINUM ALLOYS 4/9 S14 CASE STUDY II HOT CORROSION 4/16 S15 CONCLUSION SCHOOL OF ENGINEERING AND SCIENCE SPRING 1996 36431 CORROSION INSTRUCTOR: E. GUTIERREZ-MIRAVETE DAY: TUESDAY 5:30-8:30 P.M. ernesto@hgc.edu (860) 548-2464 COURSE POLICY ------------- OBJECTIVE OF THE COURSE: ------------------------ THE DEVELOP FAMILIARITY WITH THE MECHANISMS OF ENVIRONMENTALLY INDUCED DETERIORATION OF METALLIC MATERIALS IN ORDER TO BE ABLE TO OPTIMIZE THE PROCESS OF MATERIAL SELECTION FOR DEMANDING ENVIRONMENTS AND TO PREVENT CORROSION RELATED FAILURES. COURSE MATERIAL: ---------------- AN OVERVIEW OF THE MECHANISMS OF ENVIRONMENTAL DEGRADATION OF METALLIC MATERIALS. COURSE COVERS CORROSION IN BOTH DRY AND WET MEDIA. CASE STUDIES COVERING SPECIALIZED TOPICS COMPRISE THE LAST THIRD OF THE COURSE. READING ASSIGNMENTS: -------------------- MAINLY FROM THE TEXT AS INDICATED IN THE COURSE OUTLINE. READINGS MUST BE PERFORMED PRIOR TO THE DAY IN WHICH THE TOPIC WILL BE DISCUSSED IN CLASS. TERM PROJECT: ------------- EACH STUDENT WILL BE RESPONSIBLE FOR THE CONCEPTION, DEVELOPMENT, PERFORMANCE, AND REPORTING OF A TERM PROJECT. A LIST OF TENTATIVE TOPICS WILL BE PRESENTED THE FIRST DAY OF CLASS BUT INDEPENDENT PROPOSALS ARE ALSO ENCOURAGED. WRITTEN ASSIGNMENTS: -------------------- HOMEWORK WILL BE ASSIGNED REGULARLY. ANSWERS TO HOMEWORK QUESTIONS WILL BE SUBMITTED BY STUDENTS FOR GRADING VIA E-MAIL. EXAMS: ----- EXAM 1: OXIDATION AND AQUEOUS CORROSION EXAM 2: PROTECTION OF METALS AND CORROSION FAILURES COMPUTER RESOURCES: ------------------- EACH STUDENT HAS AN ACCOUNT ON THE SPARC NETWORK. STUDENTS ARE ENCOURAGED TO QUICKLY LEARN THE BASICS OF THE SYSTEM. INFORMATION ABOUT THE COURSE WILL BE REGULARLY UPDATED IN THE DIRECTORY /home/common/egm/CORR .PLEASE CHECK IT OUT. GRADING: -------- EXAM 1: 25% EXAM 2: 25% TERM PROJECT: 25% HOMEWORK: 25% OFFICE HOURS: ------------- OPEN BUT BY APPOINTMENT ONLY. CALL ME OR EVEN BETTER, USE E-MAIL TO ARRANGE MEETINGS. THE HARTFORD GRADUATE CENTER SCHOOL OF ENGINEERING AND SCIENCE SPRING 1996 36431 CORROSION INSTRUCTOR: E. GUTIERREZ-MIRAVETE DAY: TUESDAY 5:30-8:30 P.M. BIBLIOGRAPHY ------------ TEXT(S): 1.- J. C. SCULLY, "THE FUNDAMENTALS OF CORROSION", 3D. ED., PERGAMON PRESS, NEW YORK, 1990, ISBN 0-08-037874-9, $24.95 + S&H To Order: Call Butterworth-Heinemann at (617) 928-2500 2.- E. HEITZ, R. HENKHAUS AND A. RAHMEL, "CORROSION SCIENCE - AN EXPERIMENTAL APPROACH", ELLIS HORWOOD, NEW YORK, 1992, ISBN 0-13-296575-5 REFERENCE: 1.- M.G. FONTANA: "CORROSION ENGINEERING", 3D. ED., McGRAW-HILL , NEW YORK, 1986, ISBN 0-07-021463-8. 2.- G. WRANGLEN: "AN INTRODUCTION TO CORROSION AND PROTECTION OF METALS", CHAPMAN AND HALL, LONDON, 1985, ISBN 0-412-26050-6. 3.- J.M. WEST: "BASIC CORROSION AND OXIDATION", ELLIS HORWOOD, CHICHESTER, 1980, ISBN 0-85312-196-6. 4.- U.R. EVANS: "AN INTRODUCTION TO METALLIC CORROSION", 3D ED., EDWARD ARNOLD, LONDON, 1981, ISBN 0-7131-2758-9 5.- L.L. SHREIR, R.A. JARMAN AND G.T. BURSTEIN (EDS), "CORROSION" 2 VOLS, BUTTERWORTH-HEINEMAN, 1994, ISBN 0-7506-1077-8 6.- D.L. GRAVER (ED.), "CORROSION DATA SURVEY: METALS SECTION", 6TH ED. NATIONAL ASSOCIATION OF CORROSION ENGINEERS, HOUSTON, 1985, ISBN 0-915567-07-5 7.- N. BIRKS AND G.H. MEIER: "INTRODUCTION TO HIGH TEMPERATURE OXIDATION OF METALS", EDWARD ARNOLD, BALTIMORE, 1983. 8.- P. KOFSTAD, "HIGH TEMPERATURE CORROSION", ELSEVIER SCIENCE PUBLISHING CO., NEW YORK, 1988, ISBN 1-85166-154-9 THE HARTFORD GRADUATE CENTER SCHOOL OF ENGINEERING AND SCIENCE SPRING 1996 36431 CORROSION HOMEWORK PROBLEMS ----------------- 1) PROPOSE SOME TENTATIVE SUBJECT TOPICS FOR YOUR TERM PROJECT 2) WRITE THE PARTIAL REDOX REACTIONS FOR THE OXIDATION OF: Fe, Cu, Ti, Al, Ni 3) WRITE THE PARTIAL REDOX REACTIONS FOR THE REDUCTION OF: H+, O2 4) DETERMINE THE DISSOCIATION PRESSURES FOR THE FOLLOWING OXIDES (TABLE 2) Ag2O, Cu2O, PbO, NiO, FeO, ZnO, MgO, SiO2, Cr2O3, Al2O3 5) DETERMINE THE MOLAR VOLUME RATIO (OXIDE/METAL) FOR OXIDES OF THE FOLLOWING METALS Nb, Ta, Li, Na, K, Fe, Ni, Ag, Cu, Al 6) CoO IS A METAL DEFFICIENT p-TYPE SEMICONDUCTOR FORMING CATION VACANCIES AND ELECTRON HOLES. WRITE THE LIKELY OXIDATION REACTION INVOLVING DEFECTS, THE EQUILIBRIUM CONSTANT, THE EQUATION OF ELECTRONEUTRALITY AND THE RELATIONSHIP BETWEEN ELECTRONIC HOLE CONCENTRATION AND pO2 7) PREPARE A 1 PAGE TECHNICAL SUMMARY OF ONE OF THE FOLLOWING TOPICS FROM YOUR BOOK. FEEL FREE TO USE ADDITIONAL REFERENCE MATERIAL. OXIDATION RESISTANT STEELS (P. 37) OXIDATION OF ALUMINUM ALLOYS (P. 43) OXIDATION OF TITANIUM ALLOYS (P. 44) OXIDATION OF COPPER ALLOYS (P. 45) HOT CORROSION (P. 47) 8) CONSTRUCT AT LEAST THE MOST IMPORTANT LINES OF THE POURBAIX DIAGRAM OF IRON (REFERENCE: M. POURBAIX, ATLAS OF ELECTROCHEMICAL EQUILIBRIA, 2ND ED, NACE, HOUSTON, 1974, SEC. 12.1, PP. 307-321) 9) CONSIDER THE FOLLOWING KINETIC DATA IN A 1N HCl SOLUTION: PROCESS TAFEL SLOPE b (V) EXCHANGE CURRENT DENSITY io (A/cm^2) Fe -> Fe2+ 0.12 10^(-8) Zn -> Zn2+ 0.12 10^(-5) H+ -> H2 (on Fe) 0.15 10^(-6) H+ -> H2 (on Zn) 0.12 10^(-11) TABULATE AND PLOT POLARIZATION CURVES OF THE FORM E VS. log i , FIRST FOR THE CORROSION OF IRON WITH H2 EVOLUTION, THEN FOR THE CORROSION OF ZINC WITH H2 EVOLUTION. FEEL FREE TO USE PROGRAM ztafel.f (PROVIDED). NOTE: Fortran compilation is accomplished by typing: f77 ztafel.f -o ztafel Execution follows by typing: ztafel 10) PREPARE A 1/2 PAGE TECHNICAL SUMMARY OF ONE OF THE FOLLOWING TOPICS FROM YOUR BOOK. FEEL FREE TO USE ADDITIONAL REFERENCE MATERIAL. ATMOSPHERIC CORROSION OF STEELS (P. 104) ATMOSPHERIC CORROSION OF NICKEL (P. 106) 11) PREPARE A 1 PAGE TECHNICAL SUMMARY OF ONE OF THE FOLLOWING TOPICS FROM YOUR BOOK. FEEL FREE TO USE ADDITIONAL REFERENCE MATERIAL. CORROSION TESTING BY FIELD OBSERVATION (PP. 120-122) CORROSION TESTING BY ELECTROCHEMICAL METHODS (PP. 122-125) CORROSION TESTING BY IMPEDANCE METHODS (PP. 125-129) 12) USE THE COMPUTER PROGRAM PROVIDED (zgalvanic.f) TO STUDY THE GALVANIC CORROSION OF A MONEL-(70Cu-30Ni) IN A SEAWATER FILM (0.01 m THICK) AT 298 K. CONDUCTIVITY OF SEAWATER = C = 3.5 (Ohm*m)^-1 EQUILIBRIUM POTENTIAL (MONEL) = EA = 0.208 V EXCHANGE CURRENT DENSITY (MONEL) = ECURRA = 0.01 A/m^2 EQUILIBRIUM POTENTIAL (Cu-Ni) = EB = 0.063 V EXCHANGE CURRENT DENSITY (Cu-Ni) = ECURRB = 0.002 A/m^2 PARAMETERS IN BUTLER-VOLMER EQN ALFAA = 0.0130 BETAA = 0.0304 ALFAB = 0.0319 BETAB = 0.1469 NOTE: Fortran compilation is accomplished by typing: f77 zgalvanic.f -o zgalvanic Execution follows by typing: zgalvanic THE HARTFORD GRADUATE CENTER SCHOOL OF ENGINEERING AND SCIENCE SPRING 1996 36431 CORROSION SOLUTIONS TO HOMEWORK PROBLEMS (F. Edwards) ------------------------------ Problem 1 I have not yet been able to zero in on a course project topic that I feel good about. Some potential topics are: a.) Galvanic corrosion in military avionics (dissimilar metals). b.) Electrochemical corrosion in military avionics (similar or disimilar metals, voltage potential supplied by the equipment). c.) Conductive anodic coatings for use in military avionics. I am not sure at this point if the coating is conductive, or if it may just be thin enough to allow some current to pass through. The coating is used on aluminum cast chassis and allows electrical continuity between the chassis and conductive components that are connected to is physically. One trade name for the coating is "Alodine". Problem 2 Using common oxidation numbers from referenced text (*) Table 23.1: Ti --> Ti(3+) + 3e(-); Ti --> Ti(4+) + 4e(-) Cu --> Cu(+) + e(-); Cu --> Cu(2+) + 2e(-); Cu --> Cu(3+) + 3e(-) Fe --> Fe(2+) + 2e(-); Fe --> Fe(3+) + 3e(-) Using oxidation numbers from periodic table: Al --> Al(3+) + 3e(-) Ni --> Ni(2+) + 2e(-) * Chemistry Concepts and Models W. Robinson et al D.C. Heath & Co. Lexington, MA 1992 Problem 3 2H(+) + 2e(-) --> H2 O2 + 4e(-) --> 2O(2-) Problem 4 DETERMINE THE DISSOCIATION PRESSURES FOR THE FOLLOWING OXIDES (TABLE 2) Ag2O, Cu2O, PbO, NiO, FeO, ZnO, MgO, SiO2, Cr2O3, Al2O3 /_\G = RTLnPo2^n ==> Po2 = e^(/_\G/RTn) Balancing the respective equations to derive n from the MASS ACTION LAW: Me2O: 2Me + 1/2O2 --> Me2O => n = 1/2 for Me2O MeO: Me + 1/2O2 --> MeO => n = 1/2 for MeO MeO2: Me + O2 --> MeO2 => n = 1 for MeO2 Me2O3: 2Me + 3/2O2 --> Me2O3 => n = 3/2 for Me2O3 Substituting /_\G of formation from Scully Table 2 and solving for Po2; OXIDE /_\G n Po2 Ag2O -10.9 1/2 1.60 X 10^4 Atm Cu2O -145 1/2 4.19 X 10^-51 Atm PbO -188 1/2 4.8 X 10^-66 Atm NiO -215 1/2 2.0 X 10^-75 Atm FeO -255 1/2 2.5 X 10^-89 Atm @ 227degC ZnO -319 1/2 1.47 X 10^-111 Atm MgO -570 1/2 9.1 X 10^-199 Atm SiO2 -824 1 7.2 X 10^-144 Atm Cr2O3 -986 3/2 6.5 X 10^-115 Atm Al2O3 -1578 3/2 1.78 X 10^-183 Atm Problem 5 DETERMINE THE MOLAR VOLUME RATIO (OXIDE/METAL) FOR OXIDES OF THE FOLLOWING METALS: Nb, Ta, Li, Na, K, Fe, Ni, Ag, Cu, Al The Molar Volume is equal to the Molecular Weight divided by the Density. MV = MW/rho The Molar Volume Ratio is equal to the Molar Volume of the Oxide divided by the Molar Volume of the Metal. MV(Oxide)/[MV(Metal)*n] Where n = number metal atoms consumed per Mol of oxide Using these relationships, the Ratios are: OXIDE OXIDE OXIDE METAL METAL METAL MOL VL EL OXIDE MOL WT DENSITY MOL VL MOL WT DENSITY MOL VL RATIO Nb NbO 108.91 7.30 14.9 92.906 8.57 10.84 1.37 Nb NbO2 124.9 5.9 21.17 " " " 1.95 Nb Nb2O5 265.81 4.47 59.47 " " " 2.74 Ta Ta2O5 441.89 8.2 53.89 180.95 16.6 10.9 2.47 Li Li2 29.88 2.013 14.84 6.94 0.534 12.99 0.57 Na Na2O 61.98 2.27 27.30 22.99 0.971 23.68 0.567 K K2O 94.20 2.32 40.60 39.102 0.862 45.36 0.448 Fe FeO 71.85 5.7 12.61 55.847 7.874 7.09 1.78 Fe Fe2O3 159.69 5.24 30.47 " " " 2.15 Ni NiO 74.71 6.67 11.2 58.71 8.902 6.595 1.7 Ag Ag2O 231.74 7.44 31.15 107.87 10.50 10.27 1.52 Cu CuO 79.54 6.4 12.43 63.54 8.69 7.3 1.7 Cu Cu2O 143.08 6 23.85 " " " 1.63 Al Al2O3 101.96 3.965 25.72 26.98 2.699 9.997 1.29 Problem 6 CoO IS A METAL DEFFICIENT p-TYPE SEMICONDUCTOR FORMING CATION VACANCIES AND ELECTRON HOLES. WRITE THE LIKELY OXIDATION REACTION INVOLVING DEFECTS,THE EQUILIBRIUM CONSTANT, THE EQUATION OF ELECTRONEUTRALITY AND THE RELATIONSHIP BETWEEN ELECTRONIC HOLE CONCENTRATION AND pO2. a.) Oxidation reaction: 2Co + O2 = 2[] + 4(+) + 2Co b.) Equilibrium Constant: Kp = [[]^2 (+)^4]/Po2 c.) Electronegativity: [] = h/2 d.) Relationship between electronic hole concentration and Po2: h ~ Po2^(1/6) Problem 7 PREPARE A 1 PAGE TECHNICAL SUMMARY OF ONE OF THE FOLLOWING TOPICS FROM YOUR BOOK. FEEL FREE TO USE ADDITIONAL REFERENCE MATERIAL. OXIDATION RESISTANT STEELS (P. 37) OXIDATION OF ALUMINUM ALLOYS (P. 43) OXIDATION OF TITANIUM ALLOYS (P. 44) OXIDATION OF COPPER ALLOYS (P. 45) HOT CORROSION (P. 47) OXIDATION OF COPPER ALLOYS Copper alloys' oxidation kinetics are a function of temperature. At low temperatures (T < 200 C), the oxidation rate is logarithmic, while at high temperatures (T > 200 C) the rate is cubic for a small range above 200 C, then it is parabolic at higher temperatures. Activation energies of cuprous ions in Cu2O are thought to be 158 kj/mol at higher temperatures and 93 kj/mol at lower temperatures. The proportion of Cu2O to CuO is pressure and temperature dependent. At high temperatures the percentage of CuO increases and at low temperatures it decreases ( see figure 23 in Scully). At higher pressures the percentage of CuO increases, while at lower pressures it decreases. Alloying generally improves the oxidation resistance of copper by two mechanisms. First, aluminum, beryllium and magnesium, increase the oxidation resistance of copper by preferential oxidation. Preferential oxidation occurs when the solute element has a much greater affinity to oxygen than the solvent metal. In this case, the solute element would be aluminum, beryllium or magnesium, and the solvent metal is the copper. When these alloys are oxidized at high temperature, initially, cuprous oxide forms very quickly on the surface. This surface layer of cuprous oxide then retards the growth of copper oxidation while the solute element continuos to oxidize. The solute oxide forms at the metal surface under the cuprous oxide. If the concentration of the solute is high enough, it will form a protective layer of oxide that is impermeable to the passage of cuprous ions thus preventing further oxidation of the copper. The outer layer of cuprous oxide will eventually oxidize to cupric oxide. Second, other binary alloys such as Cu with Ca, Cr, Li, Mn, Si, or Ti, oxidize at a similar rate as copper. This results in a double oxide layer with CuO on the outside, and alloy oxide at the metal interface. In some cases, such as Cu with Zn greater than 20%, the outermost film will be a continuos layer of Cu2O matrix with Zn particles At low temperatures, the Zn cations lower the growth rate of Cu2O. At higher temperatures, the Zn will evaporate when it permeates the film. When reaction gases are mixed, for example O2 and SO2, corrosion resistance depends on the stability of the products with relation to the activities of the gases present. If there is thermodynamic data available, the corrosion products can likely be determined. An example is shown in Scully figure 24. In this figure, the stable phases formed on the surface of Ni at 1250K as a function of partial pressure of S and O2, are shown. The diagram shows the partial pressures at which the various elements and oxides are stable. PROBLEM 8 CONSTRUCT AT LEAST THE MOST IMPORTANT LINES OF THE POURBAIX DIAGRAM OF IRON (REFERENCE: M. POURBAIX, ATLAS OF ELECTROCHEMICAL EQUILIBRIA, 2ND ED, NACE, HOUSTON, 1974, SEC. 12.1, PP. 307-321) >From the above reference, the practical reactions for iron are: a.) Homogeneous reactions (two disolved forms): z n Reaction +2 1. Fe++ + 2H2O = HFeO2- + 3H+ +3 2. Fe+++ + H2O = FeOH++ + H+ +3 3. FeOH++ + H2O = Fe(OH)2+ + H+ +2-->+3 4. Fe++ = Fe+++ + e- +2-->+3 5. Fe++ + H2O = FeOH++ + H+ + e- +2-->+3 6. Fe++ + 2H2O = Fe(OH)2+ + 2H+ + e- +2-->+3 7. HFeO2- + H+ = Fe(OH)2+ + e- +2-->+6 8. HFeO2- + 2H2O = FeO4- - + 5H+ + 4e- +3-->+6 9. Fe+++ + 4H2O = FeO4- - + 8H+ + 3e- +3-->+6 10. FeOH++ + 3H2O = FeO4- - + 7H+ + 3e- +3-->+6 11. Fe(OH)2+ + 2H2O = FeO4- - + 6H+ + 3e- b.) Heterogenious reactions involving two solid substances: z n Reaction 0-->+2 12. Fe + H2O = FeO +2H+ + 2e- 0-->+2.67 13. 3Fe + 4 H2O = Fe3O4 +8H+ + 8e- 0-->+3 14. 2Fe + 3 H2O = Fe2O3 +6H+ + 6e- +2-->+2.67 15. 3FeO + H2O = Fe3O4 +2H+ + 2e- +2-->+3 16. 2FeO + H2O = Fe2O3 +2H+ + 2e- +2.67-->+3 17. 2Fe3O4 + H2O = 3Fe2O3 +2H+ + 2e- c.) Heterogenious reactions involving one solid substance and one dissolved substance: z n Reaction +2 18. Fe++ + H2O = FeO + 2H+ +2 19. FeO + H2O = HFeO2- + H+ +3 20. 2Fe+++ + 3H2O = Fe2O3 + 6H+ +3 21. 2FeOH++ + H2O = Fe2O3 + 4H+ +3 22. 2Fe(OH)2+ + = Fe2O3 + H2O + 2H+ c.) Heterogenious reactions involving one solid substance and one dissolved substance: z n Reaction 0-->+2 23. Fe = Fe++ + 2e- 0-->+2 24. Fe + 2H2O = HFeO2- + 3H+ + 2e- 0-->+3 25. Fe = Fe+++ + 3e- +2-->+2.67 26. 3Fe++ + 4H2O = Fe3O4 + 8H+ + 2e- +2-->+2.67 27. 3HFeO2- + H+ = Fe3O4 + 2H2O + 2e- +2-->+3 28. 2Fe++ + 3H2O = Fe2O3 + 6H+ + 2e- +2-->+3 29. 2HFeO2- = Fe2O3 + H2O + 2e- The equilibrium reactions for water are: n Reaction: a 2H+ + 2e- = H2 b 2H2O = O2 + 4H+ + 4e- For the equations and Pourbaix Diagram reference Scully chapter 2, figure 31. The hydrogen evolution reaction equation is given by: E = EoH2 + (0.0591/2)*Log[H+]2 => E = 0.000 - 0.0591*pH Plotting this equation, line a on figure 31 is obtained. The oxygen evolution reaction equation is given by: E = EoO2 + (0.0591/4)*Log{[H+]4*PO2} => E = 1.228 - 0.0591*pH Plotting this equation, line b on figure 31 is obtained. The equation for reaction #23 is given by: E = EoFe++ + (0.0591/2)*Log[Fe++] => E = -0.440 + 0.0295*Log[Fe++] The lines 23 (0, -2, -4, -6) on figure 31 are obtained by plotting this equation at activities of 100, 10-2, 10-4, 10-6. The equation for reaction #20 is given by: Log[Fe+++] = -0.72 - 3pH (from above reference) The lines 20 (0, -2, -4, -6) on figure 31 are obtained by plotting this equation at activities of 100, 10-2, 10-4, 10-6. The equation for reaction # 28 is given by: E = 0.728 - 0.1773*pH - 0.0591*Log[Fe++] (from above reference) The lines 28 (0, -2, -4, -6) on figure 31 are obtained by plotting this equation at activities of 100, 10-2, 10-4, 10-6. The equation for reaction # 26 is given by: E = 0.980 - 0.2364*pH - 0.0886*Log[Fe++] (from above reference) The lines 26 (0, -2, -4, -6) on figure 31 are obtained by plotting this equation at activities of 100, 10-2, 10-4, 10-6. The equation for reaction # 17 is given by: E = - 0.057 - 0.0591*pH (from above reference) The line 17 on figure 31 is obtained by plotting this equation. The equation for reaction # 13 is given by: E = - 0.085 - 0.0591*pH (from above reference) The line 13 on figure 31 is obtained by plotting this equation. The equation for reaction # 27 is given by: E = - 1.819 + 0.0295*pH - 0.0886*Log[HFeO2-] (from above reference) The line 27 on figure 31 is obtained by plotting this equation. The equation for reaction # 24 is given by: E = 0.493 - 0.0886*pH + 0.0295*Log[HFeO2-] (from above reference) The line 24 on figure 31 is obtained by plotting this equation. >9) CONSIDER THE FOLLOWING KINETIC DATA IN A 1N HCl SOLUTION: > > PROCESS TAFEL SLOPE b (V) EXCHANGE CURRENT DENSITY io (A/cm^2) > > Fe -> Fe2+ 0.12 10^(-8) > Zn -> Zn2+ 0.12 10^(-5) > H+ -> H2 (on Fe) 0.15 10^(-6) > H+ -> H2 (on Zn) 0.12 10^(-11) > > TABULATE AND PLOT POLARIZATION CURVES OF THE FORM E VS. log i , FIRST > FOR THE CORROSION OF IRON WITH H2 EVOLUTION, THEN FOR THE CORROSION OF > ZINC WITH H2 EVOLUTION. > >Part A - For the corrosion of iron with H2 evolution: > > The chemical reduction equation is(cathode): > > 2H+ + 2e -> H2 > > The tafel equation for hydrogen reduction is: > > E - Eo = bcLog i - ac > > where ac = bcLog io, io = 10-6 A/cm2, bc = -0.15 V > > therefore ac = (-0.15)*Log(10-6) => ac = 0.9 > > for Hydrogen, > > Eo = 0 > > Substituting Eo and ac into the above expression, > > E = -.15*Log i - 0.9 > > Substituting values for Eo and Log i and solving for E, > > E Log i > - 0.9 0 > - 0.6 - 2 > - 0.3 - 4 > 0 - 6 > > These points are plotted in E/Log i space for the hydrogen reduction line. > > > The chemical oxidation equation is (anode): > > Fe -> Fe2+ + 2e > > The tafel equation for Fe oxidation is: > > E - Eo = bALog i - aA > > where aA = bALog io, io = 10-8 A/cm2, bA = .12 V > > therefore aA = 0.12*Log(10-8) => aA = - 0.96 > > from the Pourbaix diagram for Fe, at 10^-6 activity and acidic Ph, > > Eo = - 0.6 > > Substituting values for Eo and Log i, and solving for E, > > E = .12*Log i + 0.36 > > E Log i > 0.36 0 > 0.12 - 2 > - 0.12 - 4 > - 0.36 - 6 > > These points are plotted in E/Log i space for the Fe oxidation line. > > >Part B - For the corrosion of zinc with H2 evolution: > > The chemical reduction equation is(cathode): > > 2H+ + 2e -> H2 > > The tafel equation for hydrogen reduction is: > > E - Eo = bcLog i - ac > > where ac = bcLog io, io = 10-11 A/cm2, bc = -0.12 V > > therefore ac = (-0.12)*Log(10-11) => ac = 1.32 > > for Hydrogen, > > Eo = 0 > > Substituting Eo and ac into the above expression, > > E = -.12*Log i - 1.32 > > Substituting values for Eo and Log i, and solving for E, > > E Log i > - 1.2 - 1 > - 0.84 - 4 > - 0.6 - 6 > - 0.36 - 8 > 0 - 11 > > These points are plotted in E/Log i space for the hydrogen reduction line. > > > The chemical oxidation equation is (anode): > > Zn -> Zn2+ + 2e > > The tafel equation for Zn oxidation is: > > E - Eo = bALog i - aA > > where aA = bALog io, io = 10-5 A/cm2, bA = .12 V > > therefore aA = 0.12*Log(10-5) => aA = - 0.6 > > from the Pourbaix diagram for Zn, at 10^-6 activity and acidic Ph, > > Eo = - 0.9 > > Substituting values for Eo and Log i, and solving for E, > > E = .12*Log i - 0.3 > > Substituting values for Eo and Log i, and solving for E, > > E Log i > - 0.30 0 > - 0.54 - 2 > - 0.78 - 4 > - 0.90 - 5 > > These points are plotted in E/Log i space for the Zn oxidation line. > > 10) PREPARE A 1/2 PAGE TECHNICAL SUMMARY OF ONE OF THE FOLLOWING TOPICS FROM YOUR BOOK. FEEL FREE TO USE ADDITIONAL REFERENCE MATERIAL. ATMOSPHERIC CORROSION OF STEELS (P. 104) ATMOSPHERIC CORROSION OF NICKEL (P. 106) ATMOSPHERIC CORROSION OF NICKEL The amount of humidity and contents of the atmosphere are two most important factors that determine the degree of corrosion of nickel in the atmosphere. There is a ritical humidity beyond which the degree of corrosion increases dramatically. The degree of pollution in the atmosphere is strongly related to the degree of aggressiveness of the condensation film and hence the degree of corrosion of nickel. When exposed above water, the nickel surface is covered with a layer of water that is one molecule thick at approximately 60% relative humidity and two molecules thick at approximately 90%. Hygroscopic materials on metal surface will make the layer thicker and aqueous conditions will then exist. These hygroscopic materials include carbon and ash dust both of which frequently contain sulfur and its oxides.When exposed to sulfurous atmospheres nickel develops a haze. At first, the haze can be easily wiped off but after long exposures it must be abraded off. The haze at first consists of free sulfuric acid and nickel sulfate. After long exposures, it is transformed to basic nickel sulfate. Corrosion prediction is difficult due to the complexity of the composition of atmospheres together with temperature and humidity variations. Synergistic interaction of the variables must be included for reasonably accurate predictions. One attempted prediction solution is to measure the observed corrosion rates, and the atmospheric variables, and produce an empirical equation from the data. An example of one such equation is: z = 0.16 tw^0.7 (SO2 + 1.78) Where; tw = wetness time in years, z = corrosion loss in mg/area, SO2= the concentration in m/m3. Such equations (called damage functions) always include the SO2 content of the atmosphere and the length of time the metal will be wet. Many such damage functions are much more complex that the above and contain terms for NO3^-, NOx, and Cl^-. The mathematical forms of such damage functions widely vary from location to location due to variations in local atmospheric conditions and pollution. Reference: 1. The Fundamentals of Corrosion, by J. C. Skully **************************************************************************** ******** 11) PREPARE A 1 PAGE TECHNICAL SUMMARY OF ONE OF THE FOLLOWING TOPICS FROM YOUR BOOK. FEEL FREE TO USE ADDITIONAL REFERENCE MATERIAL. CORROSION TESTING BY FIELD OBSERVATION (PP. 120-122) CORROSION TESTING BY ELECTROCHEMICAL METHODS (PP. 122-125) CORROSION TESTING BY IMPEDANCE METHODS (PP. 125-129) CORROSION TESTING BY IMPEDANCE METHODS Current flowing across a metal/solution interface can be divided in two parts: 1. The Faradaic path current due to the charge transfer process. 2. The non Faradaic current which establishes a charged interface with no charged particles crossing the interface. The impedance of such an interface can be represented by an equivalent circuit consisting of resistors and capacitors. The interface impedance will react differently depending on whether the applied voltage is D.C. or A.C.. The D.C. portion of the circuit has constant current, and the voltage (E.R) and current (I.R) are related by Ohms law, E.R=I*R.R. The A.C. portion of the circuit has an alternating signal with voltage (E.Z) and current (I.Z) out of phase. The impedance is Z and the A.C. voltage is, E.Z=I*Z.Z. The value of Z includes real resistance (R) and a complex component which is a function of the frequency, and the circuit capacitance, all of which affect not only the magnitude of Z, but its phase angle as well. The simple electrochemical interface with polarization resistance, can be represented by a resistor, to represent the polarization resistance (which constitutes the charge transfer resistance), and a parallel capacitor, to represent the double layer capacitance. This system is modeled by the following equation: Z = R.P/(1+w*2*C*2*R.P*2) - j*w*C*R.P*2/(1+w*2*C*2*R.P*2) + R.S Where; w = frequency in radians/sec, j is the imaginary operator SQRT(-1), C is the capacitance in microfarads, R.P is the real parallel resistance in ohms, and R.S is the real circuit resistance which is in series with the parallel combination of R.P and C. Using a test circuit such as the one in Scully figure 39, current measurements are made as a function of frequency. Frequency values in the range of 0.1 - 10 kHz are considered the most suitable. The signal is a small A.C. voltage impressed on a D.C. voltage. The signal should be sufficiently small so as to insure that the response of the system is a linear function of the amplitude of the input. The real current is in phase with the input voltage and the imaginary current is out of phase by 90^o with the input voltage (lagging). The measured values of current are used to calculate impedance at the different frequencies and the imaginary impedance is plotted against the real impedance (see Scully figure 72). At low frequencies, the capacitor blocks the current and the impedance of the system is the real impedance, R.S + R.P. At high frequencies, the capacitor exhibits a very low impedance (approaching a high frequency short circuit) and the impedance of the system is RS. Thus the polarization impedance can be calculated. The double layer capacitance (C) can be calculated from the following formula: C = 1/(4*pi*f*Z.max) Where Z.max is the maximum value of the imaginary impedance from the plot. For diffusion controlled processes, two resistors in parallel with the capacitor are used in the model (Scully figure 73). The resistor R.t represents the charge transfer resistance and R.d represents the diffusion resistance. At low frequencies, a line of unit slope is obtained corresponding to the Warbug impedance (Z.w). The Warbug impedance is related to the Warbug coefficient (s) and the frequency (w, in radians/sec) by the relationship: Z.w = SQRT(2*s)/SQRT(w) The diffusion coefficient can be calculated from s. Reference: 1. The Fundamentals of Corrosion, by J. C. Skully 12) USE THE COMPUTER PROGRAM PROVIDED (zgalvanic.f) TO STUDY THE GALVANIC CORROSION OF A MONEL-(70Cu-30Ni) IN A SEAWATER FILM (0.01 m THICK) AT 298 K. CONDUCTIVITY OF SEAWATER = C = 3.5 (Ohm*m)^-1 EQUILIBRIUM POTENTIAL (MONEL) = EA = 0.208 V EXCHANGE CURRENT DENSITY (MONEL) = ECURRA = 0.01 A/m^2 EQUILIBRIUM POTENTIAL (Cu-Ni) = EB = 0.063 V EXCHANGE CURRENT DENSITY (Cu-Ni) = ECURRB = 0.002 A/m^2 PARAMETERS IN BUTLER-VOLMER EQN ALFAA = 0.0130 BETAA = 0.0304 ALFAB = 0.0319 BETAB = 0.1469 I solved this problem by entering the above parameters in "zgalvanic.f" as follows: ------------------------------------------------------------------------- CHAPTER 2 INPUT DATA C C NX=NXP1-1 NY=NYP1-1 C C CONDUCTIVITY OF ELECTROLYTE (Ohm*m)^-1 C C = 3.5 C C EQUILIBRIUM POTENTIALS (V), EXCHANGE CURRENT DENSITIES (A/m^2) AND C B-V EQUATION PARAMETERS (V) FOR METALS A AND B C EA = 0.208 EB = 0.063 C ECURRA = 0.01 ALFAA = 0.0130 BETAA = 0.0304 C ECURRB = 0.002 ALFAB = 0.0319 BETAB = 0.1469 C C GEOMETRY OF THE CORRODING AREA C XA = SIZE OF METAL A EXPOSED TO ELECTROLYTE C XB = SIZE OF METAL B EXPOSED TO ELECTROLYTE C YTOTAL = THICKNESS OF ELECTROLYTE LAYER C XA = 0.01 XB = 0.01 YTOTAL = 0.01 C C ITERATION PARAMETERS C OM = 1.6 ITMAX = 9000 EPS = 2E-6 C C -------------------------------------------------------------------- Note I changed EPS to 2E-6 because the MAXIMUM RESIDUAL was not converging and was oscillating between approximately 1.1E-06 and 1.67E-06. The results are given below: ITERATIONS CONVERGED ITERATION NO. = 3600 MAXIMUM RESIDUAL = 0.189221E-05 X(I) PCURR(I) cur 2.00000E-02 1.82498E-02 X(I) E(I,1) pot1 2.00000E-02 0.135596 X(I) E(I,NYP1) pot2 2.00000E-02 0.135625