Research On Preparation Of Composite Metal Film For Fiber Optic Corrosion Sensor

Reinforced structures are widely used in ships,industrial buildings and buried metal pipelines.However,due to the existence of metal corrosion that cannot be eliminated,the structural damage life is shortened,the safety problems are prominent,and huge economic losses are brought about.The corrosion monitoring of reinforcement can provide a basis for evaluating the structural safety.The traditional corrosion detection method is mostly electrochemical method,but it has some problems such as large equipment,complex installation,inaccurate monitoring and so on.In recent years,optical fiber corrosion sensors made of optical fiber are popular because of their advantages such as small size,anti-magnetic interference,easy installation and accurate monitoring accuracy.The complex chemical reaction between carbon steel and the surrounding environment occurs in the steel reinforcement structure.The Fe-C alloy fiber optic corrosion sensor can accurately monitor the corrosion of steel reinforcement.In this paper,the silicon dioxide fiber as the substrate material,respectively by electroless nickel plating and magnetron sputtering method to prepare excessive metal films,and then by electroplating thickening Fe-C alloy metal.The main work of this paper includes the following three aspects:(1)The fiber pretreatment process:The fiber has small diameter and high brittleness.It is necessary to remove the coating layer completely and then prepare the metal of certain thickness on the surface of the fiber core.Residual coating layer will lead to difficult coating,poor adhesion and other problems,coating chemical etching coarsening needs to precisely remove the coating,otherwise excessive corrosion damage core.The coating can be completely removed by removing the coating with Miller pliers,wiping the residue with acetone,coarsening solution consisting of 100 m L/L HF(50%),NH4 F 400 g/L,coarsening temperature of 30 ℃ and average etching time of 1.5 h.(2)The preparation process of the intermediate layer:The fiber is not conductive,so fe-C film cannot be obtained directly by electroplating.It is necessary to prepare a layer of metal film with good conductivity and compact structure first,and then electroplating thickening.The intermediate films were prepared by PVD magnetron sputtering and acidic chemical nickel respectively.PVD is affected by the lack of cavity size and process parameters optimization of magnetron sputtering machine,the coating obtained by PVD is not as good as electroless plating as a whole,and the bonding force is poor.Electroless plating added complexing agent and stabilizing agent to obtain nickel film uniform and compact,binding force meets the requirements,high temperature treatment without peeling without thorn.Nickel conductivity is good,can meet the subsequent electroplating thickening requirements.The plating solution has good stability and can be continuously plated.The thickness of electroless plating can reach5～10 μm.(3)The electroplating process of Fe-C alloy:The addition of ascorbic acid and citric acid can affect the carbon content of the coating,and p H and temperature have great influence on the appearance and density of the coating.The electroplating process parameters were optimized by single factor and orthogonal experiment as follows: ferrous sulfate as main salt,sodium dodecylate 0.2 g/L,sodium saccharin 1～1.5 g/L,citric acid 2 g/L,ascorbic acid 7 g/L,temperature 30 ℃,p H 3,cathode current density 0.3～1.0 A/dm2,and uniform cathode movement..