The objective of this project was to achieve pre-demonstration development of controlled-release corrosion inhibitors as alternatives to hexavalent chromium [Cr(VI)] (chromate)-containing primers. The Limited Scope Study was directed to achieve the following objectives:
- Scale-up of materials that can meet MIL-PRF-23377 (solvent-based primer).
- Provide evidence of resistance to aircraft alkaline cleaners and deicing fluids.
- Provide formulation for initial ecological and toxicity screening.
- Submit an interim report that will provide the basis for a future ESTCP demonstration effort.
Autonomic Materials Inc. achieved the scalability of the encapsulation process for two corrosion inhibitors by starting with a thorough assessment of the laboratory scale process, designed to optimize parameters including surfactant type, surfactant concentration, process temperature profile, process duration, and micro particle yield per batch. Evidence of resistance to alkaline cleaners and aircraft deicing fluids and compliance with MIL-PRF-23377 was gathered by replacing the inhibitor package, of a primer that meets the MIL-PRF-23377 requirements, with an encapsulated inhibitor and self-healing microcapsules. The properties of the primer formulation, that were expected to change, were tested to demonstrate that the primer still met the MIL-PRF-23377 requirements.
The scale-up of the inhibitor encapsulation process for two corrosion inhibitors to the 2.0 kilograms scale was achieved successfully; evaluation of primer formulations, that incorporated the encapsulated corrosion inhibitors and self-healing agents, provided evidence that the primer formulations met most of the MIL-PRF-23377 requirements and showed sufficient resistance to alkaline cleaners and aircraft deicing fluids; an initial ecological and toxicity screening, on the encapsulated inhibitor formulation, by the Army Public Health Center concluded that most of the proposed components are of low to moderate toxicity and are not a significant concern.
This new technology will lead to environmentally friendly alternatives to hexavalent chromium that will enable the Department of Defense to protect its assets. The scalability of the technology was achieved to a scale that will accommodate a follow on field demonstration effort. The encapsulation technology is currently being evaluated by several industry partners for licensing. Licensing, qualification, and commercialization will allow its real world utilization.