Aluminum Manganese Molten Salt Plating
NAVAL AIR SYSTEMS COMMAND PATUXENT RIVER MD MATERIALS ENGINEERING DIV
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In 1999 an effort was begun to evaluate the efficacy of a production size aluminum-manganese molten salt plating system. The technology was previously demonstrated at a smaller scale through efforts overseen by Naval Air Warfare Center, Warminster and Naval Air Systems Command, Patuxent River. The effort begun in 1999 culminated in a 200-gallon demonstration system installed at Naval Air Depot North Island. In mid-September 2005 the aluminum manganese plating system located at the depot was loaded with an initial batch of plating chemicals. However, after loading 25 gallons of chemicals into the tank the researchers were directed by the depot Environmental Office to stop due to visible stack emissions. Initially a scrubber was planned for the process that would remove alumina particulate and neutralize hydrogen chloride vapor generated by the plating system. However, the scrubber was not included in the final design. The San Diego Air Pollution Control District concluded that a scrubber was not needed based on estimated emissions the researchers submitted in the air permit application. Although the estimated content and amount of emissions was acceptable to the District they did not understand that the emissions would be visible. The District does not allow any visible emissions from any stack, a rule that the researchers were unaware of until personnel from the depot Environmental Office observed the emissions and directed the process to be stopped. Several mechanical methods and addition of fume suppressant to the bath were implemented in an effort to reduce emissions visibility. Emissions were significantly reduced but not enough to satisfy the District rule. Fuming of the bath resulted in loss of bath chemicals, as well as crusting of ventilation and plating tank inner surfaces. The crust is a hard, non-brittle alumina coating that forms when volatile bath components condense on relatively cooler surfaces. Both issues hindered the ability to operate the process.
- Inorganic Chemistry
- Coatings, Colorants and Finishes
- Metallurgy and Metallography