An optical fibre corrosion sensor with an electroless deposit of Ni–P

The feasibility of an optical fibre corrosion sensor (OFCS) is studied. A PCS fibre is metallised with chemical nickel–phosphorus deposit on an uncladded part of 2 cm length. The light power (P) transmitted through the fibre is registered as a function of the angle of incidence (α) of the light emitted by a laser diode at 670 nm wavelength. The P(α) curves are modified when the nickel coating is corroded in phosphoric acid solutions, the full width of these curves at half-maximum increases when the density of corrosion pits increases. Kinetic curves of the corrosion are determined in different concentrations of phosphoric acid. This type of corrosion sensor can be inserted in structures in order to follow in situ the corrosion state of the structure.