| Cathodic protection technology is commonly used as protection methods of metal cin marine environment.By applying cathodic polarization on the metal surface,a dense calcareous deposits can be formed to cover the metal surface,which can reduce the current density and increase the cathodic protection efficiency,thus saving the cost of cathodic protection.The current state of art indicates that research on the formation process of calcareous deposits mainly focused on Q235 steel.The characterization on stainless steel,copper alloy and other marine engineering materials are relatively less concerned and lacked of systematic analysis.In present paper,several technologies were used to analyze polarization behavior and the formation process of calcareous deposits of Q235 steel,high manganese aluminum bronze and 304 stainless steel,including potentiodynamic polarization,potentiostatic polarization,electrochemical impedance spectroscopy(EIS),micro morphology(SEM),elements analysis(EDS),phase composition analysis(XRD),electrochemical test and microscopic analysis method.Taking Q235 steel as an example,the influence of cathodic polarization on the different damage rate of coated steel breakage were analyzed to evaluate the protection effect.Through the above research,the following conclusions are obtained:1.The potential range of cathodic protection for different metal materials is different due to the influence of processing and properties of materials.Data from polarization curves indicates that the suitable range is-0.75V～-1.0V for Q235 steel,-0.83V～-0.53V or 304 stainless steel-0.90V～-0.50V and f and high manganese aluminum bronze.2.Cathodic polarization has different effects on the formation process and protective effect of calcareous deposits on different metal materials.For Q235 steel,-1.0V has the higher protection efficiency than-0.8V;Cathodic polarization has influence both on passive film and calcareous deposits,corn shape calcareous deposits formed on 304 SS at-0.8V with main composites of aragonite calcium,while it has higher density and resistance than Q235.The passive film of 304 SS is reduced during polarization and then forms again,the main content is Fe(III).The current density required at-0.5V is lower than at-0.8V.The passive film of the 304 SS grow thicker as polarization progresses,which reaches to the value 22.5kΩ·cm2 after 168 h.Thus the protection efficiency under-0.5V is higher than-0.8V;For high manganese aluminum bronze,calcareous has a certain effect on the protection efficiency,while the passive film has little effect on the protection efficiency.The current density for maintaining-0.8V is smaller than-0.5V for high manganese aluminum bronze.The density of calcareous deposits at-0.8V is higher than-0.5V,thus lead to the lower current density requirement.3.Cathodic polarization has different effects on the formation process and protective effect of calcareous deposition layer on the surface of coated steel with different breakage rates.For the coating steel with damage rate of 4%,the stable current density at-1.0V the polarization potential is lower,the calcareous deposit has higher resistance and more compact morphology.For the coating steel with damage rate of 1%,although the stable current density is high under the polarization potential of-1.0V,the resistance of calcareous deposition layer is higher and the morphology is more compact.Therefore,-1.0V can be used as cathodic protection for damaged coated steel.At the polarization potential of-0.8V,corrosion products were formed at the damaged sites.Therefore,-0.8V can not be used as cathodic protection for damaged coated steel.The above research provides important theoretical basis and data support for the design of cathodic protection and maintenance of current in typical metal materials and damaged coated steel in marine engineering. |
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