Mechanistic Model for Open-circuit Metal-ion-catalyzed Aluminum Dissolution Oscillation Reactions

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Mechanistic Model for Open-circuit
Metal-ion-catalyzed Aluminum Dissolution
Oscillation Reactions

• A. Scheeline and E. A. De Lucia,
• University of Illinois at Urbana-Champaign
• C. Cobb, C. East, G. Ferrer, R. Fuller,
• J. Josephs, I. S. Kim, M. McCutcheon,
• F. Onyemauwa, and N. Sethi,
• Augusta State University

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History of Oscillatory Aluminum Electrochemistry

• Hudson and Tsotsis 1994 cites 8 papers since 1828
• A. Pocius, 1988-1992, observes rest potential
  oscillation for type 2024 Al in chromic acid
• C. Cobb notes oscillation on type 1100 Al in HNO3
  containing Hg2

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Types of Oscillations

• Gas evolution
• Electrochemical hysteresis loop (per M. Koper)
• Oxide film formation and cracking

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Example of Hg2-Catalyzed Oscillatory Oxidation
of Type 1100 Aluminum Rod
Vs. Pt Pseudo-reference Electrode
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Temperature/Potential Correlation
Vs. Ag/AgSO4 Reference
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Temperature/Potential (Scale-Expanded)
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Oscillations at Rotating Disk Electrode
nt 24000 rpm s. Implies second-order process.
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Scale-expanded Potential Excursion
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Al 1100 Coil Hg2
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Evolution of Pd Film on Al
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Pd2/HNO3 Al/Al2O3 Surface, Post-Excursion
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Qualitative Model
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Components of Model I

• Mass Transfer to RDE. For HM00.62
  D02/3w1/2n-1/6 40 mm s-1_at_400 rpm
• Stress in Oxide Film (Sato, Electrochim. Acta,
  1971)
• Nernstian Behavior of Each Species

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Components of Model II

• Bubble burst heat transfer and mass transfer to
  be dealt with heuristically
• Heat conduction into electrode
• Convective heat transfer in fluid (Levich)
• Oxide growth and defects (Macdonald)

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Relevant Potentials I

• Al2O3 6H 6e 2 Al 3 H2O E0 ? -1.5
  0.039 pH V at 25C
• Aluminum passivates at 1.8 V vs. SHE
• Hg2 2e Hg E0 0.851 V
• Hg22 2e 2Hg E0 0.796 V
• 2H 2e H2 E0 0 (defined) Based
  on M. Pourbaix and CRC Tables

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Relevant Potentials II

• O2 4H 4e 2H2O E0 1.229 V
• NO3- 2H e NO2 H2O E0 0.95 V
• Cu2 2e Cu ?? E0 0.340 V
• Based on CRC Tables

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Qualitative Model
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Funding

• UIUC DOE Grant DE-FG02 96ER45607 (Office of
  Basic Energy Sciences)
• ASU donors of the Petroleum Research Fund,
  administered by ACS

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Acknowledgements

• Husheng Gao
• Ewa S. Kirkor
• Nagi Suzuki
• SCS Machine Shop
• SCS Electronics Shop
• Charles F. Zukoski

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Citations

• C. Y. Chao, L. F. Lin, and D. D. Macdonald, A
  Point Defect Model for Anodic Passive Films. I.
  Film Growth Kinetics, J. Electrochem. Soc. 128,
  1187-1194 (1981).
• L. F. Lin, C. Y. Chao, and D. D. Macdonald, A
  Point Defect Model for Anodic Passive Films. II.
  Chemical Breakdown and Pit Initiation, J.
  Electrochem. Soc. 128, 1194-1198 (1981).
• N. Sato, A Theory for Breakdown of Anodic Oxide
  Films on Metals, Electrochim. Acta, 19,
  1683-1692 (1971).
• V. G. Levich, Physicochemical Hydrodynamics,
  Prentice Hall, Englewood Cliffs, NJ (1962).

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Composition of Al Type 1100

• SiFe lt1
• Cu 0.05-0.2
• Mn 0.05
• Zn 0.1
• Other lt0.05 each, lt0.15 total
• Al 99