Scientific Understanding of the Mechanisms of Non-Chromate Corrosion Inhibitors

WP-1621

Objective

WP-1621 Project Graphic

Schematic of ring-disc electrode with the ability to perform Surface Enhanced Raman Spectroscopy (SERS) and induce mechanical damage in situ.

Hexavalent chromium (Cr[VI]) has been extensively used in conversion coatings and paints to protect against corrosion of aluminum and iron-based alloys in Department of Defense systems. However, chromate-based inhibitor systems are being eliminated due to the toxicity and carcinogenicity of Cr(VI). The Occupational Safety and Health Administration recently lowered the permissible exposure limit by a factor of twenty. The environmental and health concerns associated with Cr(VI) have led to the development of a broad range of nonchromate alternatives. Most of these alternatives individually are not as effective as chromates; however, a combination of them may be found to be a suitable replacement. A lack of complete understanding of the mechanism of these alternative inhibitors is the greatest impediment to success in finding such suitable combinations.

The objective of this project is to gain understanding of the mechanism of selected alternative inhibitors under realistic metallurgical and environmental conditions in order to facilitate development of nonchromate inhibitor systems that are as effective as those of chromates.

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Technical Approach

Using standard and multielectrode electrochemical techniques and scratching electrode techniques, researchers will assess the anodic and cathodic inhibition functions of nonchromate inhibitors. The adsorption characteristics and concentration of adsorbed species on the alloy surfaces will be determined using X-ray photoelectron spectroscopy (XPS) and Mott-Schottky analysis. Interactions between the inhibitors and heterogeneities in the microstructures will be investigated using multielectrode and microelectrochemical techniques. The effect of alternating wet and dry conditions and the drying process on inhibition mechanisms also will be analyzed. Based on mechanistic studies of the individual inhibitors, researchers will systematically investigate theeffect of inhibitor combinations. An operational model will be developed to identify new, optimum combinations of nonchromate inhibitors whose individual properties are synergistically enhanced. The project will focus on both aluminum alloy and steel.

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Benefits

The results will be applicable to a variety of weapons systems and ground support equipment. Detailed knowledge of the mechanism of the inhibitors will enable a more scientific approach to selecting the optimum combinations to achieve the corrosion protection required by the application. The outlined techniques also will provide an experimental framework to study future nonchromate inhibitor candidates. (Anticipated Project Completion - 2012)

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Points of Contact

Principal Investigator

Dr. Florent Bocher

Southwest Research Institute

Phone: 210-522-5240

Fax: 210-522-6965

Program Manager

Weapons Systems and Platforms

SERDP and ESTCP

Document Types

  • Fact Sheet - Brief project summary with links to related documents and points of contact.
  • Final Report - Comprehensive report for every completed SERDP and ESTCP project that contains all technical results.
  • Cost & Performance Report - Overview of ESTCP demonstration activities, results, and conclusions, standardized to facilitate implementation decisions.
  • Technical Report - Additional interim reports, laboratory reports, demonstration reports, and technology survey reports.
  • Guidance - Instructional information on technical topics such as protocols and user’s guides.
  • Workshop Report - Summary of workshop discussion and findings.
  • Multimedia - On demand videos, animations, and webcasts highlighting featured initiatives or technologies.
  • Model/Software - Computer programs and applications available for download.
  • Database - Digitally organized collection of data available to search and access.