106 Chapter 2 9. The spontaneity of a reaction depends upon more than just the heat of reaction. To predict stability, one must consider also the entropy. 10. If the reaction is spontaneous, the change in free energy is negative, whereas if the reaction is in equilibrium, the free energy change is equal to zero. 11. The real problem with predicting whether a reaction may take place or not is in selecting the proper reaction to evaluate. Care must be taken not to overlook some possible reactions. 12. Since the corrosion of ceramics in service may never reach an equilibrium state, thermodynamic calculations cannot be strictly applied because these calculations are for systems in equilibrium. Many reactions, however, closely approach equilibrium, and thus the condition of equilibrium should be considered only as a limitation, not as a barrier to interpretation of the data. 13. There is a general tendency for oxides to be reduced at higher temperatures at constant oxygen partial pressures. One should be aware that any metal will reduce any oxide above it in the Ellingham diagram. 14. Unit activity should be applied only to species in the pure state. 15. The most important parameter of corrosion from the engineering viewpoint is the reaction rate. 16. Diffusion coefficients depend upon the composition and structure of the material through which diffusion occurs. 17. The rate of the reaction expressed as the rate of change of concentration, dc/dt, depends upon the concentration of the reactants. 18. The discrepancies between the experimental data and the theoretical models are often due to nonspherical particles, a range in sizes, poor contact between reactants, formation of multiple products, and the dependency of the diffusion coefficient upon composition. 19. Arnold et al. [2.141] concluded that dynamic thermogravimetric studies provide insufficient data Copyright © 2004 by Marcel Dekker, Inc. Fundamentals 107 for calculation of reaction kinetics, that the data are influenced by the experimental procedures, and that the results are uncertain. 20. The enthalpy of the reaction is often sufficient to raise or lower the sample temperature by as much as 1000°C. 21. The flow of material by diffusion is proportional to the concentration gradient and is directed from the region of high concentration to one of low concentration. 22. In isometric crystals, the diffusion coefficient is isotropic, as it is in polycrystalline materials as long as no preferred orientation exists. 23. In most real cases, the diffusion coefficient can vary with time, temperature, composition, or position along the sample, or any combination of these. 24. Silica-forming reactions are the most desirable for protection against oxygen diffusion. 25. A diffusion flux will set up a thermal gradient in an isothermal system. 2.11 ADDITIONAL RELATED READING Vetter, K.J. Electrochemical Kinetics; Academic Press, New York, 1967. Bockris, O.M.; Reddy, A.K.N. Modern Electrochemistry; Plenum Press, New York, 1970; Vol. 2. Shaw, D.J. Charged Interfaces. Introduction to Colloid and Surface Chemistry, 3rd Ed.; Butterworths, London, 1980; 148–182. Chp. 7. Marshall, C.E. The Physical Chemistry and Mineralogy of Soils: Soils in Place; Wiley & Sons: New York, 1977; Vol. II. Reviews in Mineralogy: Mineral-Water Interface Geochemistry; Hochella, M.F. Jr., White A.F., Eds.; Mineral. Soc. Am., Washington, DC, 1990; Vol. 23. Burns, R.G. Mineralogical Applications of Crystal Field Theory; Cambridge University Press: Cambridge, 1970. Shackelford J.F., Ed.; Bioceramics, Applications of Ceramic and Glass Materials in Medicine; Trans Tech Publications: Switzerland, 1999. Copyright © 2004 by Marcel Dekker, Inc. 108 Chapter 2 Reviews in Mineralogy: Health Effects of Mineral Dusts. Guthrie, G.D. Jr.; Mossman B.T., Eds.; Mineral. Soc. Am., Washington, DC, 1993; Vol. 28. P.G.Shewmon. Diffusion in Solids. J.Williams Book Co., Jenks, OK, 1983. 2.12 EXERCISES, QUESTIONS, AND PROBLEMS 1. Discuss the reaction products that may form and how they may relate to any interfacial reaction layer formed. 2. If a “unified theory of corrosion of ceramics” were to be developed, what structural characteristic would be included and why? 3. Look up the vapor pressure of several materials to confirm the concept that covalent materials vaporize more quickly than ionic materials due to their higher vapor pressure. 4. Why does the corrosion rate decrease when a thermal gradient is present? 5. The Arrhenius equation has been used to represent the temperature dependence of corrosion. Discuss when this equation is most appropriate and why. 6. Discuss the difference between direct and indirect dissolution. What other terms are used to describe these types of dissolution? 7. What is the most predominant parameter in the equation for corrosion rate under free convection? Why is this parameter more predominant than the others? 8. Discuss the various problems relating to the experimental verification of the galvanic corrosion of ceramics. 9. Describe how the cross-linking of silica tetrahedra affect corrosion in silicates by aqueous solutions. 10. How does pH affect the corrosion of crystalline ceramics and how does this relate to isoelectric point (IEP)? Copyright © 2004 by Marcel Dekker, Inc. Fundamentals 109 11. Discuss the difference between electrochemical and chemical dissolution. What material parameters are important in each type? 12. Describe how one tells whether solid-solid corrosion occurs by bulk, grain boundary, or surface diffusion. REFERENCES 2.1. Phase Diagrams for Ceramists. Vol. I-XII, Am. Ceram. Soc., Westerville, Ohio. 2.2. Cooper, A.R. The use of phase diagrams in dissolution studies. In Refractory Materials; Alper, A.M., Ed.; Academic Press: New York, 1970; Vol. 6-III, 237–250. 2.3. Kramer, D.P.; Osborne, N.R. Effects of atmosphere and dew point on the wetting characteristics of a glass-ceramic on two nickel-based superalloys. In Ceramic Engineering and Science Proceedings; Smothers, W.J., Ed.; Am. Ceram. Soc. Westerville, Ohio, 1983; 4 (9–10), 740–750. 2.4. Noyes, A.A.; Whitney, W.R. Rate of solution of solid materials in their own solutions. (Ger) Z.Physik. Chem. 1897, 23, 689–692. 2.5. Nernst, W. Theory of reaction velocities in heterogeneous systems. (Ger) Z.Physik. Chem. 47, 52–55. 2.6. Berthoud, A. Formation of crystal faces. J.Chem. Phys. 10, 624–635, 1912. 2.7. Prandtl, L. NACE Tech. Memo. No. 452, 1928. 2.8. Levich, B.G. Physicochemical Hydrodynamics; Prentice Hall: Englewood Cliffs, NJ, 1962. 2.9. Levich, E.G. Theory of concentration polarization. Discuss. Faraday Soc. 1, 37–43, 1947. 2.10. Cooper, A.R., Jr.; Kingery, W.D. Dissolution in ceramic systems: I, Molecular diffusion, natural convection, and forced convection studies of sapphire dissolution in calcium aluminum silicate. J. Am. Ceram. Soc. 1964, 47 (1), 37–3. 2.11. Samaddar, B.N.; Kingery, W.D.; Cooper, A.R., Jr. Dissolution in ceramic systems: II, Dissolution of alumina, mullite, Copyright © 2004 by Marcel Dekker, Inc. 110 Chapter 2 anorthite, and silica in a calcium-aluminum-silicate slag. J. Am. Ceram. Soc. 1964, 47 (5), 249–254. 2.12. Oishi, Y.; Copper, A.R., Jr.; Kingery, W.D. Dissolution in ceramic systems: III, Boundary layer concentration gradients. J. Am. Ceram. Soc. 1965, 48 (2), 88–95. 2.13. Hrma, P. Contribution to the study of the function between the rate of isothermal corrosion and glass composition. (Fr) Verres Refract. 1970, 24 (4–5), 166–168. 2.14. Lakatos, T.; Simmingskold, B. Influence of constituents on the corrosion of pot clays by molten glass. Glass Technol. 1967, 8 (2), 43–47. 2.15. Lakatos, T.; Simmingskold, B. Corrosion effect of glasses containing Na 2 O-CaO-MgO-Al 2 O3-SiO 2 on tank blocks Corhart ZAC and sillimanite. Glastek. Tidskr. 1967, 22 (5), 107–113. 2.16. Lakatos, T.; Simmingskold, B. Influence of viscosity and chemical composition of glass on its corrosion of sintered alumina and silica glass. Glastek. Tidskr. 1971, 26 (4), 58–68. 2.17. Chung, Y D.; Schlesinger, M.E. Interaction of CaO-FeO- SiO 2 slags with partially stabilized zirconia. J. Am. Ceram. Soc. 1994, 77 (3), 612. 2.18. Pons, A.; Parent, A. The activity of the oxygen ion in glasses and its effect on the corrosion of refractories. (Fr) Verres Refract. 1969, 23 (3), 324–333. 2.19. Blau, H.H.; Smith, C.D. Refractory problems in glass manufacture. Bull. Am. Ceram. Soc. 1950, 29 (1), 6–9. 2.20. Woolley, F.E. Prediction of refractory corrosion rate from glass viscosity and composition. In UNITECR ’89 Proceedings; Trostel, L.J., Jr., Ed.; Am. Ceram. Soc. Westerville, OH, 1989, 768–779. 2.21. Fox, D.S.; Jacobson, N.S.; Smialek, J.L. Hot corrosion of silicon carbide and nitride at 1000°C. In Ceramic Transactions: Corrosion and Corrosive Degradation of Ceramics; Tressler, R.E., McNallan, M., Eds.; Am. Ceram. Soc. Westerville, OH, 1990; Vol. 10, 227–249. 2.22. Jacobson, N.S.; Stearns, C.A.; Smialek, J.L.Burner rig Copyright © 2004 by Marcel Dekker, Inc. Fundamentals 111 corrosion of SiC at 1000°C. Adv. Ceram. Mater. 1986, 1 (2), 154–161. 2.23. Cook, L.P.; Bonnell, D.W.; Rathnamma, D.Model for molten salt corrosion of ceramics. In Ceramic Transactions: Corrosion and Corrosive Degradation of Ceramics; Tressler, R.E., McNallan, M., Eds.; Am Ceram. Soc. Westerville, OH, 1990; Vol. 10, 251–275. 2.24. Gordon, S.; McBride, B.J. Computer Program for Calculation of Complex Chemical Equilibrium Compositions, Rocket Performance, Incident & Reflected Shocks, and Chapman- Jongnet Detonations. 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Soc. 1964, 47 (2), 90–94. 2.31. Busby, T.Hotter refractories increase the risk of downward drilling. Glass Ind. 1992, 73 (1), 20, 24. 2.32. Lasaga, A.C. Atomic treatment of mineral-water surface reactions. In Reviews in Mineralogy, Mineral-Water Interface Geochemistry; Hochella, M.F., Jr., White, A.F., Eds.; Mineral. Soc. Am. Washington, DC, 1990; Vol. 23, 17–85. Chp. 2. Copyright © 2004 by Marcel Dekker, Inc. 112 Chapter 2 2.33. Marshall, C.E. The Physical Chemistry and Mineralogy of Soils: Soils in Place; Wiley & Sons: New York, 1977; Vol. II. 2.34. Huang, P.M.Feldspars, olivines, pyroxenes, and amphiboles. In Minerals in Soil Environments; Dinauer, R.C., Ed.; Soil Sci. Soc. Am. Madison, WI, 1977, 553–602. Chp. 15. 2.35. Casey, W.H.; Bunker, B.Leaching of mineral and glass surfaces during dissolution. In Reviews in Mineralogy, Vol. 23: Mineral-Water Interface Geochemistry; Hochella, M.F., Jr., White, A.F., Eds.; Mineral Soc. Am. Washington, DC, 1990; Vol. 23, 397–426. Chp. 10. 2.36. Borchardt, C.A. Montmorillonite and other smectite minerals. In Minerals in Soil Environments; Dinauer, R.C., Ed.; Soil Sci. Soc. Am. Madison, WI, 1977, 293–330. Chp. 9. 2.37. Schnitzer, M.; Kodama, H. Reactions of minerals with soil humic substances. In Minerals in Soil Environments; Dinauer, R.C., Ed.; Soil Sci. Soc. Am. Madison, WI, 1977, 741–770. Chp. 21. 2.38. Jennings, H.M. Aqueous solubility relationships for two types of calcium silicate hydrate. J. Am. Ceram. Soc. 1986, 69 (8), 614–618. 2.39. Marshall, C.E. The Physical Chemistry and Mineralogy of Soils: Soil Materials; Krieger Publishing Company: Huntington, NY, 1975; Vol. I. 2.40. Elmer, T.H. Role of acid concentration in leaching of cordierite and alkali borosilicate glass. J.Am.Ceram. Soc. 1985, 68 (10), C273-C274. 2.41. Burns, R.G. Mineralogical Applications of Crystal Field Theory; Cambridge University Press: London, 1970; 162– 167. 2.42. Hawkins, D.B.; Roy, R. Distribution of trace elements between clays and zeolites formed by hydrothermal alteration of synthetic basalts. Geochim. Cosmochim. Acta 1963, 27 (165), 785–795. 2.43. Shaw, D.J. Charged interfaces. Introduction to Colloid and Surface Chemistry, 3rd Ed.; Butterworths: London, 1980; 148–182. Chp. 7. 2.44. Brady, P.V.; House, W.A. Surface-controlled dissolution and Copyright © 2004 by Marcel Dekker, Inc. Fundamentals 113 growth of minerals. In Physics and Chemistry of Mineral Surfaces; Brady, P.V., Ed.; CRC Press: New York; 1996, 225– 305. Chp. 4. 2.45. Parks, G.A. The isoelectric points of solid oxides, solid hydroxides, and aqueous hydroxo complex systems. Chem. Rev. 1965, 65 (2), 177–198. 2.46. Diggle, J.W. Dissolution of oxide phases. In Oxides and Oxide Films; Diggle, J.W., Ed.; Marcel Dekker: New York, 1973; Vol. 2, 281–386. Chp. 4. 2.47. Bright, E.; Readey, D.W. Dissolution kinetics of TiO 2 in HF- HCl solutions. J. Am. Ceram. Soc. 1987, 70 (12), 900–906. 2.48. 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In Application of Science in Examination of Works of Art; Joung, W.J., Ed.; Museum of Fine Arts: Boston, 1973. 2.54. Skoulikidis, T.N. Atmospheric corrosion of concrete reinforcements, limestones, and marbles. In Atmospheric Corrosion; Ailor, W.H., Ed.; John Wiley & Sons: New York, 1982; 807–825. 2.55. Amoroso, G.G.; Fassina, V. Stone Decay and Conservation; Elsevier: Amsterdam, 1983; 12. 2.56. Hoffmann, M.R.Fog and cloud water deposition. In Materials Degradation Caused by Acid Rain; ACS Symposium Series Copyright © 2004 by Marcel Dekker, Inc. 114 Chapter 2 318; Baboian, R., Ed.; Am. Chem. Soc. Washington, DC, 1986; 64–91. 2.57. Mulawa, P.A.; Cadle, S.H.; Lipari, F.; Ang, C.C.; Vandervennet, R.T. Urban dew: Composition and influence on dry deposition rates. In Materials Degradation Caused by Acid Rain, ACS Symposium Series 318; Baboian, R., Ed.; Am. Chem. Soc. Washington, DC, 1986; 61–91. 2.58. Semonin, R.G. Wet deposition chemistry. 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Chemistry of Metals; McGraw-Hill: New York, 1 953 ; 348–349 2.134 Lou, V.L.K.; Mitchell, T.E.; Heuer, A.H Review—Graphical displays of the thermodynamics of high-temperature gassolid reactions and their application to oxidation of metals and evaporation of oxides J Am Ceram Soc 19 85, 68 (2), 49 58 2.1 35 Quets, J.M.; Dresher, W.H Thermochemistry of the hot corrosion of superalloys J Mater 1969, 4 (3), 58 3 59 9... D.E Reactions of bioactive borate glasses with physiological liquids Glass Res 2002–2003, 12 (1–2), 21–22 2.89 Bauer, J.F Corrosion and surface effects of glass fiber in biological fluids Glass Res 2000, 9 (2), 4 5 2.90 Kubaschewski, O.; Hopkins, B.E Oxidation of Metals and Alloys; Butterworths: London, 1962 2.91 Readey, D.W Gaseous corrosion of ceramics In Ceramic Transactions, Corrosion and Corrosive... Thermodynamics of vaporization of Cr2O3: Dissociation energies of CrO, CrO2 and CrO3 J Chem Phys 1961, 34 (2), 664–667 2.94 Graham, H.C.; Davis, H.H Oxidation/vaporization kinetics of Cr2O3 J Am Ceram Soc 1971, 54 (2), 89–93 2. 95 Pilling, N.B.; Bedworth, R.E The oxidation of metals at high temperature J Inst Met 1923, 29, 52 9 59 1 2.96 Jorgensen, P.J.; Wadsworth, M.E.; Cutler, I.B Effects of oxygen partial... 1984, 89, 217–2 25 2.112 Van Brakel, J.; Modry, S.; Svata, M Mercury porosimetry: State of the art Powder Technol 1981, 29, 1–12 2.113 Rootare, H.M.; Nyce, A.C The use of porosimetry in the measurement of pore size distribution in porous materials Int J Powder Metall 1971, 7(1), 3–11 2.114 Smith, C.S.Grains, phases, and interpretation of microstructure Trans AIME 1948, 1 75 (1), 15 51 2.1 15 White, J Magnesia-based... Practical use of mercury porosimetry in the study of porous solids Powder Technol 1981, 29, 45 52 2.110 Lapidus, G.R.; Lane, A.M.; Ng, K.M.; Conner, W.C Interpretation of mercury porosimetry data using a pore-throat network model Chem Eng Commun 19 85, 38, 33 56 2.111 Conner, W.C.; Lane, A.M Measurement of the morphology of high surface area solids: Effect of network structure on the simulation of porosimetry... however, some of the more important data do not exist for one reason or another For example, maybe the oxygen partial pressure was not determined during the duration of the service life of the ceramic In some cases, it may be impossible to collect certain pieces of data during the operation of the particular piece of equipment At these times, a knowledge of phase equilibria, thermodynamics, and kinetics... reactions: (3.1) and (3.2) the partial pressure of oxygen is given by: (3.3) where k1 and k2 are the equilibrium reaction constants For constant ratios, the partial pressure of oxygen is independent of the total pressure Thus these gas mixtures provide a means to obtain a range of oxygen pressures Several techniques to mix these gases are discussed by Macchesney and Rosenberg [3.6] In the study of corrosion. .. another form of surface analysis, in question can be a very enlightening experiment In this way, the depth of penetration can be determined and the elements that are the more serious actors can be evaluated Lodding [3.14] has provided an excellent review of the use of SIMS to the characterization of corroded glasses and superconductors Determination of surface structures of ceramics for corrosion studies... have a thorough understanding of the environment where the ceramic is to be used and must select the portions of the environment that may cause corrosion For example, it is not sufficient to know that a furnace for firing ceramicware is heated by fuel oil to a temperature of 1200°C One must also know what grade fuel oil is used and the various impurities contained in the oil and at what levels In addition,... Symposium Proceedings: Materials Stability and Environmental Degradation; Barkatt, A Verink, E.D., Jr., Smith, L.R., Eds.; Mat Res Soc.: Pittsburgh, PA, 1988; Vol 1 25, 53 –60 2.131 Ellingham, H.J.T Reducibility of oxides and sulfides in metallurgical processes J Soc Chem Ind 1944, 63, 1 25 2.132 Richardson, F.D.; Jeffes, J.H.E The thermodynamics of substances of interest in iron and steel making from . metals and evaporation of oxides. J. Am. Ceram. Soc. 19 85, 68 (2), 49 58 . 2.1 35. Quets, J.M.; Dresher, W.H. Thermochemistry of the hot corrosion of superalloys. J. Mater. 1969, 4 (3), 58 3 59 9. 2.136 4 5. 2.90. Kubaschewski, O.; Hopkins, B.E. Oxidation of Metals and Alloys; Butterworths: London, 1962. 2.91. Readey, D.W. Gaseous corrosion of ceramics. In Ceramic Transactions, Corrosion and. D.S.; Jacobson, N.S.; Smialek, J.L. Hot corrosion of silicon carbide and nitride at 1000°C. In Ceramic Transactions: Corrosion and Corrosive Degradation of Ceramics; Tressler, R.E., McNallan, M.,