Study And Design For A United Protection System Of Coating And Electrochemical Protection With Carbon Fiber Anode Embedded In Coating

The present dissertation studies a new cathodic protection system, inwhich carbon fiber sparse gauze was embedded in the coating andemployed as anode. Since carbon fiber anode and the metal base cathodeare parallel and have the same area, the power lines are parallel and thus aeven protection could be achieved. Although carbon fiber is electricallyconductive, its electric resistance is still not negligible. So thisdissertation emphasizes the study of the effect of carbon fiber resistanceon the distribution of cell voltage along the direction remote from powersource. Two mathematical models of current introduction from bothsingle side and double side for the computation of cell voltagedistribution were established respectively. The relation betweenprotection distance and the parameters of section area, inter-stranddistance of carbon fiber and coating resistance is discussed. A test ofelectric resistance network of which the values of resistance were knownwere carried out and the result shows the measured and theoreticalpotential distribution curves overlap each other, validating the correctnessof the mathematic model. A long specimen test result shows a good agreement between the theoretical and measured potential distributioncurves. In this long specimen test, taking advantage of the stability of thepotential for carbon fiber anode in a certain range of anodic current, thecell voltage distribution was successfully converted into potentialdistribution on the protected metallic base, demonstrating the feasibilityand guiding role of the mathematic model.The advantage of carbon fiber gauze anode is the possibleapplication in the field where the separated anodes are difficult to installand the field where the resistance of the medium is too high and there isno enough space for anodes to install in remote places. Another field isthe ship hull protection, for which the separated anodes protrude from thehull surface about several centimeters, leading to some additional sailingresistance. But in my study, the anode and reference electrode are allembedded in the coating. So the additional sailing resistance would bedecreased considerably. In this dissertation, a detailed discussion isemphasized on ship protection.AC impedance measurement was employed to select optimalprotection potential. The polarization behavior of the carbon fiber, theinstallation of zinc reference electrode and the potential control measureare also discussed.