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Development and Evaluation of a Permanent Reference Electrode, 18-9463

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Principal Investigators
Frank Song
Sean Brossia
Narasi Sridhar

Inclusive Dates:  02/01/04 - 06/01/04

Background - Permanent reference electrodes (PRE) are used to help control cathodic protection systems in mitigating corrosion of underground pipelines and storage tanks. The most commonly used commercial PRE, copper-copper sulfate (CSE), experiences problems including: (1) the need for periodic internal electrolyte replacement as a result of seasonal wet/dry cycles of soil, (2) conglomeration of copper sulfate crystals at the electrode tip resulting in loss of connection between the electrode and the soil, and (3) leakage of the copper sulfate electrolyte into the surrounding soil resulting in loss of electrolyte, possible deposition of copper on metal surfaces and accelerated corrosion of the structure. Malfunction of CSE results in increasing corrosion costs and reduced safety.

Approach - Tungsten/tungsten oxide (WWO) electrodes are rugged and easy to fabricate. They have long been used as pH electrodes, which, if surrounded by a buffered solution with a constant pH, would be able to function as a PRE. If the electrolyte salts in the PRE are hygroscopic, the WWO reference electrode (WWO_RE) would be expected to work in wet/dry cyclic soils; its electrolyte would not aggregate or leak easily or if leaked out, the electrolyte would not accelerate corrosion of the structure.

Accomplishments - The project demonstrated that WWO_REs performed effectively in conditions challenging to CSEs. Packed with their dry electrolyte salts (dry PREs) and tested in dry sand with controlled relative humidity (RH) (Figure 1), the dry CSE never recovered to function (not shown) while the dry WWO_RE did (Figure 2). This study noted that WWO_RE functions in dry soils and does not require electrolyte replenishment upon dryout. It would work as a PRE under storage tanks to protect the tank bottom. Long-term tests under field conditions are needed to better understand WWO_RE performance.

PRE manufacturers are being contacted to evaluate the commercial value of the new PRE and for possible support for further understanding the performance of the PRE. A paper has been accepted and is to be presented at the NACE conference in April 2005 in Houston, Texas. Meetings and discussion on the PRE are expected.

Figure 1. Buried in sand of controlled RH, the potential of a steel rebar (center) is measured by CSEs and WWO_REs. Figure 2. In relatively dry sand (55% RH), dry WWO_RE recovered to function while the dry CSE never did (the CSE potential varied randomly, not shown).

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