Rock Martineau, engineer at Surface Optics Corporation, conducts in-field cleanliness verification on an F/A-18 aircraft wing at the North Island NAVDEP.

Real-time methods to provide qualitative and quantitative assessment of surface cleanliness are required in a variety of military applications. The availability of a convenient analysis technology for on-site determination of surface contamination allows more rapid and accurate assessment of the efficiency of chosen cleaning techniques. It reduces hazardous materials usage, handling, and disposal, and improves alternative cleaning products and processes.

A number of Department of Defense sites are in need of this technology for applications such as coating, plating, and bonding aircraft component surfaces, where thin layers of contaminants — invisible to the naked eye — can wreak havoc on subsequent surface processes, and cause part failures in future service.

A Collaborative Effort
The Naval Facilities Engineering Service Center (Port Hueneme, CA) recently partnered with Sandia National Laboratories (Livermore, CA) under a Strategic Environmental Research and Development Program sponsorship to fund Surface Optics Corporation (San Diego, CA) in the development of a portable Fourier transform infrared spectroscopy (FTIR) instrument. It is based on absorption of a grazing-incidence infrared beam reflected from the surface of interest.

Grazing-angle reflectance FTIR is an established laboratory technique for the detection of low-level surface contamination; however, it had not previously been transitioned into a small, portable device for on-site, real-time analysis.

Recently, applications at the North Island Naval Aviation Depot (NADEP) in California benefited from the use of the portable grazing-angle FTIR instrument. This military organization performs a variety of depot maintenance functions for fighter aircraft.

Results of On-site Testing
North Island aircraft maintenance personnel desired a simple method to detect hydrocarbon contamination on aluminum aircraft skin prior to coating application. A demonstration of the portable FTIR device was conducted on a dichromate conversion-coated aluminum wing of an F/A-18A aircraft.

The aircraft was located in a North Island NAVDEP maintenance hangar. The wing in question had been cleaned earlier in the day, in preparation for coating. The optical monitor detected a small amount of hydrocarbon contamination — invisible to the naked eye — on the wing’s surface. This led hangar personnel to check the adequacy of their cleaning method and allowed them to make more informed decisions for subsequent action.

North Island personnel were also interested in monitoring the deposition of a novel trivalent chromium conversion-coating on aluminum aircraft parts. This new treatment process results in a very thin oxide coating on the metal surface that is virtually invisible to the naked eye. Shop personnel were searching for a method to confirm that the coating had "taken" on the metal surface during the treatment process. The FTIR device was able not only to detect the trivalent chromium coating, but it also enabled shop personnel to distinguish it chemically from a conventional dichromate conversion-coating. In addition, the relative thickness of the coating can be determined by the intensity of the spectral peaks.

Theresa Hoffard is a research chemist at the Naval Facilities Engineering Service Center (Port Hueneme, CA).