Optical-Fiber Corrosion Sensor Based on Deposit of Au/Ni–P

Abstract

The realization of an optical-fiber corrosion sensor (OFCS) has been achieved using two different methods. In the first method, a plastic clad silica (PCS) fiber whose uncladded part (2 cm in length) has been metallized through deposition using nickel–phosphorus. In the second method, metallization used gold and nickel–phosphorus. The light power [P(α)] at the exit end of the fiber is recorded as a function of the angle (α, angle of incidence) made by the axis of the fiber and a beam from a laser diode at a 670 nm wavelength applied at the entrance of the fiber. It is observed that the corrosion of the coating material (nickel–phosphorus) modifies the P(α) curves, be it by immersion in phosphoric acid solutions. The full width at half-maximum of these curves increases with increasing corrosion pit density. Kinetic curves of corrosion have been obtained for different concentrations of phosphoric acid. This type of sensor is important because it can be inserted in metallic infrastructures to monitor the corrosion state of the structure in situ.