Fiber-Optic Chloride Sensor Development

Abstract

Chloride in the form of salt water is a major contaminant of ground water, percolating through landfill liners and causing corrosion of steel. Four fiber-optic sensors capable of detecting chloride concentrations were developed. The most promising sensor detects chloride concentrations from 100 μg/mL to greater than 3,000 μg/mL. This sensor works when the chloride changes a reddish-brown silver chromate strip to white silver chloride. The color change causes the intensity of light propagating through the fiber to increase. The increase is monitored, and a calibration curve depicting light intensity versus chloride concentration results. The most promising sensor was multiplexed to determine the diffusion coefficients of chloride in a saturated sand column. The development, operation, and sensitivity of the sensors are described. Upon further development the sensor could be placed in the soil or in reinforced concrete for in situ monitoring of chloride. The sensor's advantages over electronic sensors include immunity to corrosion and electromagnetic interference, and the ability for multiplexing sensors onto a single fiber.