Cyclic Polarization Laboratory

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Cyclic Polarization Laboratory

• Corrosion Behavior of Medical Devices
• MatE 210
• at
• CTC United Defense
• March 15, 2004

Reference Denny A. Jones, Principles and
Prevention of Corrosion, Second Edition, Prentice
Hall, Upper Saddle River, NJ (1996)
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Cyclic Polarization for Medical Devices

• Theory of Technique
• Applicable Standards
• Experimental Issues
• Experiments -- Off to the lab
• Lab Report Requirements Professor Guna

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Theory of Cyclic Polarization

• What is Corrosion?
• gtDestruction or deterioration of a metal or
  alloy because of reaction with the environment.
• gtExtractive metallurgy in reverse
• gtWastage or loss of a material
• Can be wet or dry.
• Different forms exist.
• Thermodynamics describes the driving force, ?G gt
  0, favors the reaction

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Theory of Cyclic Polarization

• Corrosion occurs by independent, electrochemical,
  half cell reactions at local anodes cathodes.
• Typical anodic reactions
• Fe -gt Fe2 2e-
• Ni -gt Ni2 2e-
• Typical cathodic reactions
• 2H 2e- -gt H2 (acids)
• 2H2O 2e- -gt H2 2OH-
• O2 2H2O 4e- -gt 4OH-

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Theory of Cyclic Polarization

• Cyclic Polarization
• An experimental technique
• Perturbs the surface of a metal or alloy
• Measures the Voltage versus Current response
• Obtains information about the reactions occurring
  at the surface
• Ebd and Eprot

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Theory of Cyclic Polarization

• Anodic polarization to a level to cause breakdown
  of the passive film formed on the metal surface,
  Ebd.
• Reverse polarization direction to establish
  whether or not the surface re-passivates, Eprot.

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Applicable Standard

• ASTM F-2129-03
• Electrochemical apparatus
• Specimen configuration
• Solutions
• Evaluation of small implant devices, most
  frequently stents.

• Determine corrosion behavior by extracting
  results from Voltage vs. Current Density response
  of the specimen and record pH of solution.
• Ecorr, corrosion potential
• Icorr, corrosion current density
• Corrosion Rate, mpy or µm/yr
• Ebd, breakdown potential
• Eprot, protection potential
• Efinal, final potential reverse
• Examine for corrosion

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Experimental Issues

• Specific conditions
• Surface area of the specimen
• Equivalent weight of the alloy
• Scan rate
• Initial final pH
• Temperature of the solution
• Solution concentration
• Deaerated with N2
• Stereo Exam

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Report Requirements