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A series of SECM image maps of the localized electrochemical response at a Stainless 304 surface. This response identifies corrosion pits in the material. Each image required ~50 minutes to acquire.

INL is studying the effects of various non-corrosion mechanisms on reactive surfaces, with particular emphasis on 300 series stainless steel, a common construction material.

Localized Corrosion is a broad term that embodies a number of specific non-uniform corrosion mechanisms: pitting corrosion, crevice corrosion, stress-corrosion cracking (SCC), corrosion fatigue (CF), intergranular and transgranular dissolution, etc. Much of our interest has centered upon the phenomenon of pitting corrosion, especially in 300 series stainless steels.

Using a homebuilt scanning electrochemical microscope (SECM), we map the electrochemical activity present at a reactive surface. SECM involves rastering a small electrochemical sensor (microelectrode) in a plane parallel to the surface of interest, but displace from the surface by a distance no greater than the microelectrode’s diameter.

Our SECM operates in a four-electrode configuration which permit independent control of both the potential at the working electrode (specimen) and the potential applied to the microelectrode probe. This probe can be operated either in an amperometric (current signal) or potentiometric (potential signal) mode. Typically we operate our SECM in a substrate generation / tip collection (SG/TC) mode, whereby the specimen is biased to a potential where local breakdown is probable, then the tip is held at a potential where we observe the reduction of an indicator molecule, such as potassium iodide. Our SECM is modeled after a conventional design obtained from our collaborator, Henry White. The instrument is controlled by Labview software written in-house. One of the unique facets to the INL program is development of dynamic SECM imaging whereby changes in surface maps are tracked as a function of time (see Figure).

Recently, we have begun significant work on increasing the temporal resolution of our SECM. One of the ways we have accomplished this is by designing constructing and testing our new Microelectrode Array Electrochemical Microscope (MEA-ECM). Additionally we have built a selective area dissolution system using a homebuilt microelectrochemical cell and microbore capillary, as initially designed by Suter and Bohni. This system fits on our Nikon microscope and allows us to seek out localized sites on the surface of a material then position the capillary above an individual site and examine its dissolution.

Apparati: For more information about these instruments, see the capabilities page.

• Homebuilt Scanning Electrochemical Microscope (SECM)
• Homebuilt Microelectrode Array Electrochemical Microscope (MEA-ECM)
• Homebuilt Capillary Microelectrochemical Cell System
• Gamry FAS1 Femtostat
• Sutter Instruments P-2000 Laser Based Micropipette Puller
• FEI Environmental Scanning Electron Microscope (ESEM)
• Perkin-Elmer Phi 4300 Scanning Auger Microprobe (SAM)

Peer-Reviewed Publications:

T.E. Lister and P.J. Pinhero, “The Effect of Localized Electric Fields on the Detection of Dissolved Sulfur Species from Type 304 Stainless Steel Using Scanning Electrochemical Microscopy,” Electrochmica Acta (Submitted 12/02).

T.E. Lister, R.E. Mizia, P.J. Pinhero, “In Situ Imaging of Corrosion Events in Austenitic Steels by Scanning Electrochemical Microscopy,” NACE Corrosion/2003, Paper 03379, San Diego, CA.

T.E. Lister and P.J. Pinhero, Scanning Electrochemical Microscopy Study of Corrosion Dynamics on Type 304 Stainless Steel, Electrochemical and Solid State Letters 11, B33 (2002).