Volume 8, Number 2     March/April 2000

Safer, Environmentally Friendly Coating Developed

Use of chromate-based conversion coatings for aluminum generates health and safety concerns because of their toxicity and carcinogenic nature. Conversion coatings are metal-surface coatings consisting of a compound of the base metal used to convert the metal’s surface to a corrosion-resistant state. Chromates have been found to cause irritation of the respiratory tract, produce ulcerations and perforations of the nasal septum and cause dermatitis, skin sensitization, asthma and lung cancer. Until recently, however, there was no alternative.

An environmentally friendly aluminum coating for government and industrial applications has resulted from a collaboration with Lynntech, Inc., of College Station, Texas, and NASA’s Kennedy Space Center in Florida. Lynntech participated with Kennedy’s Materials Science Division under a Small Business Innovation Research (SBIR) contract to develop a molybdate-based conversion coating for aluminum and aluminum alloys. This innovation, called "Molyseal," does not contain chemicals or materials that are hazardous or toxic or give rise to health and safety concerns.

Lynntech has applied for several patents relating to this technology and has formed an alliance with multiple partners in the metal finishing industry. Because Lynntech is a technology innovation and development company, its goal is to move this innovation to the precommercial stage, secure appropriate patent rights and then license the technology to an interested manufacturer for entry into the commercial sector. The commercialization strategy includes third-party validation of the technology provided by leading end users of chromium conversion processes through in-kind testing.

Molyseal can be applied by dipping, painting or spraying, with short treatment times at low temperatures, and is compatible with existing cleaning and pretreatment procedures. Only commercially available chemicals and materials are used, which do not require special storage provisions and can be easily adapted into existing application methods. Lynntech envisions government and science applications in U.S. military missiles, NASA spacecraft and Department of Defense prime contractors. Industrial applications include aerospace, boilers, air conditioners and aluminum construction materials.

At Kennedy, NASA has used chromate-based coatings on many of its spacecraft and desires to replace these harmful chemicals with safer coatings. Until the successful formulation of Molyseal, NASA had no other alternatives. Future Kennedy operational use of this coating includes the Space Shuttle orbiters, the solid rocket boosters and other NASA spacecraft and aircraft.

Chemical conversion coatings on aluminum alloys to achieve long-term corrosion resistance of painted spacecraft and aircraft structures have found widespread military and commercial applications. With increasing environmental regulations, the use of chemical conversion coatings that do not contain harmful chemicals is of particular interest to NASA, the Department of Defense and other federal agencies.

Alternatives for chromate conversion coatings that exhibit the same corrosion resistance and that are formulated from environmentally acceptable chemicals are greatly needed. Molyseal provides both features. Tests demonstrate an exceptional corrosion resistance of the new coating prepared from formulations consisting of molybdates and several important additives. Some Molyseal coatings outperformed the chromate-based conversion coatings in electrochemical corrosion-resistance tests and passed a standard 336-hour salt fog test. These results established a sound technical feasibility for this new molybdate conversion coating.

For more information, contact Thomas Gould at Kennedy Space Center. 321/867-6238, Thomas.Gould-1@kmail.ksc.nasa.gov Please mention you read about it in Innovation.