| In recent years as a quickly developed new sensor, optical fiber corrosion sensorhas been widely applied to metal corrosion monitoring because of its significantadvantages such as small size,light weight, inherent immunity to electromagneticfields, distributed sensing and compatibility with optical fiber data communicationsystems can be easily integrated into a concrete structural system. Among the variousoptical fiber corrosion sensors, an optical fiber corrosion sensor with Fe-C sensitivefilm is regard as one of the most promising sensor for its simple structure and notrequired sophisticated testing equipment, however some deficiencies still exist inpractical application. In order to improve performance of the optical fiber corrosionsensor with Fe-C sensitive film and promote its application in practical engineering, asensor with step type Fe-C sensitive film which can improve sensitive and monitoringrange is proposed and investigated in this paper.The technique of preparing Fe-C sensitive film on optical fiber with the methodof electroplating associated with magnetron sputtering has been groped by exploringoptimize the preparation process parameters. The step type Fe-C sensitive film wasprepared by insulating in electroplating process based on this technique. The analysistechniques, such as SEM, EDS, XRD were used to study the structure parameters ofthe Fe-C sensitive film. The results showed that Fe-C sensitive film distributes evenaround the fiber core, and had good surface condition.The sensing law of optical fiber sensor with Fe-C sensitive film in differentthickness was investigated. The output power was improved at the beginning ofcorrosion, and the time that the output power reaches the maximum value was shorter,when thickness of Fe-C sensitive film was small enough. As the thickness of Fe-Csensitive film increased, the output power was substantially smooth at the beginningof corrosion and improved at the end of corrosion, the moment that output powerobviously improved was prolonged. The output power of step type Fe-C sensitive film was improved at the beginning of corrosion and the time that output power reachedmaximum value was prolonged. The step type Fe-C sensitive film not only has thegreat sensitivity of thin film but also has the wild monitoring range of thick film, cansignificantly improve performance of this type sensor.The change of Fe-C sensitive film surface morphology with corrosion wasstudied. At the beginning of corrosion, corrosive medium could easily permeate intothe film due to the local damage of the film, which could resulted in roughening of thefilm and enhanced absorption of light energy. As a result, the output power wouldslightly decrease. With the corrosion process, the thickness of Fe-C sensitive film wasgradually reduced, fiber core was surrounded by corrosion solution and air andconditions of total reflection was satisfied, the output power of optical signal wouldobviously increase.The effect of Cl-on the corrosion behavior of Fe-C sensitive film in simulatedconcrete pore solution was studied. The results showed that with increase of theconcentration of Cl-, the change trend of Ecorrand Rpof Fe-C sensitive film wassimilar to reinforcing steel, which could be able to simulate the corrosion behavior ofreinforcing steel. The sensing law of optical fiber sensor with Fe-C sensitive film inCl-solution was studied. The results showed that the change of output optical powerwas complicated in Cl-solution, but in the whole it was increased, the value of outputoptical power increased was little. Further research is needed to explore the reliablesensing law of Fe-C sensitive film in Cl-solution for practical application.A system was designed to study the sensing law of Fe-C sensitive film indistributed corrosion monitoring. The results showed that the optical power losscaused by Fe-C sensitive film would be gradually decreased during corrosion process;the corrosion information of this point might be obtained through loss change ofoptical power. Moreover, multiple sensors had no effect on each other. It is importantfor optical fiber sensor with Fe-C sensitive film applied to roads, bridges and otherprojects in corrosion monitoring. |
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