Elaboration and standardization of an optical fibre corrosion sensor based on an electroless deposit of copper M. Benounis a,b , N. Jaffrezic-Renault a,* , G. Stremsdoerfer a , R. Kherrat b a Laboratory of Engineering and Functionalization of Surfaces, UMR CNRS 5621, Ecole Centrale de Lyon, BP 163, 69134 Ecully Cedex, France b Laboratory of Physicochemistry of Interfaces, Annaba University, BP 139, Oued Kouba, Annaba, Algeria Abstract The goal of our present work is to develop and test an optical fibre corrosion sensor (OFCS) fabricated by an electroless copper film deposition onto an optical fibre core within the sensing region. In our case, corrosion monitoring was carried out by two methods: optical and electrochemical methods. The idea consists is to couple these two methods by correlating the parameters describing the optical detection and those which describe the electrochemical corrosion process. This approach, once is carried out, makes it possible to gain more precise information on degradation within hidden parts of metallic structures. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Optical fibre sensor; Corrosion; Potentiometric detection 1. Introduction Degradation by corrosion of industrial plants or other types of metallic structure is a persistent problem, which at best can only be contained but never totally eliminated. Thus, a strong demand for in situ monitoring of corrosion exists. Hidden sensors included in structures, which could give an early indication of corrosion without significant disassembly, could reduce the cost of maintenance. Sensors based on optical fibres are good for this purpose due to their small diameter (<1 mm), to their flexibility and to the feasibility of remote sensing. Previous works present different examples of the use of optical fibres for in situ monitoring of the durability of materials and structures. An uncladded optical fibre can be used to follow the life cycle of a composite material by monitoring the variation of the refractive index of the resin matrix [1]. Metallised optical fibres have been developed in order to monitor corrosion in aeronautical structures [2]. In reference [3], is reported the research on optical fibre corrosion sensors (OFCSs) fabricated by electroplating an Fe–C alloy film onto an optical fibre core within the sensing region. In our laboratory, [4] we demonstrated the feasibility of an optical fibre corrosion sensor when the sensing region of the optical fibre was metallised with an electroless nickel– phosphorus deposit. In these papers concerning OFCS, it was shown that an optical signal (optical power transmitted P) varies when metal is corroded, however, the optical signal was not analysed, no relation was shown between this variation and the rate and type of corrosion of the metal. This paper deals with an optical fibre corrosion sensor metallised with copper. The objective of the work is to relate the variation of an optical signal (in connection with P versus a, angle of incidence) with the rate and type of corrosion of copper in acidic media. This optical fibre corrosion sensor was fabricated by electroless copper plating onto an optical fibre core within the sensing region. A change in the concentration of corrosion products in acidic solution can also be determined by a simple measurement of the electrochemical potential of a platinum electrode, after standardization. 2. Experimental and principles 2.1. Preparation of the metallised fibres In our experiments, the fibres used were PCS fibres provided by Quartz and Silica Company with a core dia- meter of 400 mm. The numerical aperture of this PCS fibre is sin a NA ¼ 0:48 with a NA ¼ 28:58. When the injection angle of the light is less than the value of a NA , total internal Sensors and Actuators B 90 (2003) 90–97 * Corresponding author. Tel.: þ33-4-72-18-62-43; fax: þ33-4-78-33-11-40. E-mail address: nicole.jaffrezic@ec-lyon.fr (N. Jaffrezic-Renault). 0925-4005/03/$ – see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0925-4005(03)00050-9