The introduction of new environmentally acceptable cleaning solvents for chlorinated hydrocarbon materials has led to uncertainties in standard cleaning procedures. As a result, many applications over utilize solvents to ensure component cleanliness and the success of any subsequent processing operations (such as coating, bonding, or plating). This practice, in turn, leads to the additional usage, handling and disposal of waste streams, while inefficiently using personnel operating time. Currently, the detection of surface contamination on reflective surfaces is most conveniently and rapidly performed by the Fourier Transform Infrared (FTIR) reflectance method which provides both quantitative and qualitative information on surface coatings. However, it is greatly limited in its ultimate sensitivity to surface contaminants by the nature of its optical design.
The objective of this project is to develop real-time methods that provide both qualitative and quantitative assessments of surface cleanliness for a wide variety of military cleaning applications. Two prototype infrared-optical instruments with complementary capabilities will be built to aid in reducing the use, emission and handling of hazardous materials in cleaning operations.
Sandia National Laboratory (DOE) in partnership with Naval Facilities Engineering Service Center (NFESC) will develop two prototype instruments with complementary capabilities for cleaning verification. In both cases, surface contamination at very low levels of concentrations will be detected by measuring the grazing-incidence infrared reflectance of the surface. The first instrument is based on a widely tunable infrared-laser with high speed surface-imaging capability but is limited to the detection of organic contaminants. The second instrument is an optimized FTIR spectrometer with high sensitivity for organic and inorganic species on a variety of surfaces but has limitations on speed and surface coverage for real-time analysis of surface contaminants. The instruments differ in the nature of the information they provide. The first produces images that directly indicate the spatial extent and location of contamination, while the second provides a spectrally-resolved measurement of the surface reflectance at a single point.
Detection of residual hydrocarbon contaminants with spatial distribution has been demonstrated in the laboratory by an imaging tunable infrared-laser instrument. Image sizes are currently 1.5 inches squared (in2), and detection limits are a few milligrams per feet squared (mg/ft2). A compact prototype instrument with increased sensitivity and image size is being constructed that will be suitable for field measurement. With Surface Optics Corp., an optimized grazing-angle sampling head for a portable FTIR spectrometer has also been developed. Detection limits with this instrument are a few tenths mg/ft2, and the sampling head is now commercially available. The prototype instrument has been successfully demonstrated in the field at NAVDEP North Island and Hill Air Force Base. Work continues to improve the overall prototype design and transition the technology to the DoD user community.
These new monitoring technologies provide real-time, non-contacting surface cleanliness measurements that will provide the Department of Defense (DoD) community, as well as the Department of Energy and commercial sector, with the capability of fine-tuning cleaning procedures for optimum process efficiency while reducing the volume of waste streams generated.