FT-IR Optical Fiber Remote Detection of Aluminum Hydroxide by Evanescent Wave Absorption Spectroscopy

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Abstract
Remote detection of very small amounts of aluminum hydroxide has been achieved with the use of evanescent wave absorption spectroscopy. Aluminum hydroxide is a principal corrosion product of aluminum. Five absorption bands have been recorded in the spectral range from 3350 to 3650 cm−1. The recorded positions, transition strengths, and widths of the absorption bands are in qualitative agreement with reference spectral data. A four-wavenumber-resolution Michelson interferometer and decoated 200-μm-core-diameter multimode chalcogenide optical fibers were combined to make the evanescent wave absorption measurements. One-to four-meter lengths of fiber were used with 15 to 25 cm of the fibers decoated. The technique is very sensitive and can detect a very small amount of aluminum hydroxide in contact with the decoated fiber core. This study is a valuable step in the development of a technique for monitoring industrial corrosion of aluminum alloys.