| Iron and steel materials are widely used in ocean engineering equipment and marine structures,due to it,s low price and excellent performance.However,corrosion of them is easy to occur because of the transmission medium and outside environment,which can result in serious consequences and huge economic losses.At present,anti-corrosion coating and cathodic protection have been used widely in marine engineering equipment protection.Calcareous deposit was formed on the surface of metal by cathodic protection.Fouling organisms live in marine widely.The formation of calcareous deposit is inevitably affected by biofouling.And,the calcareous deposit will also affect the adhesion of microorganism.However,the interrelationship between biological and calcareous layers is rarely studied.Therefore,the objective of this paper is to study the interaction between the cathodic protection of the calcareous layer and the adhesion of microorganisms.Objective to investigate the corrosion behavior of the Q235 carbon steel and the pre-deposited calcareous layer in the microalgae environment,and it provided a theoretical basis for the protection of marine metals.In this paper,calcareous layer was deposited on the surface of Q235 carbon steel by galvanostatic polarization.Compared with Q235 bare steel,the effect of calcareous layer on the adhesion of microalgae was studied by fluorescence microscopy.The corrosion behavior of the Q235 carbon steel and the pre-deposited calcareous layer in the environment of seawater and microalgae were investigated by using surface analysis techniques and electrochemical measure method.Calcareous layer formed on Q235 carbon steel was acquired by applying galvanostatic polarization in nature seawater under laboratory conditions.It was found that the calcareous layer prepared by depositing for 72 h exhibited a current density of-30 uA/cm2.The calcareous deposit prepared with this parameter had the best crystal structure and smooth surface.With the increase of time,the polarization potential of the material became more negative,and reached hydrogen evolution potential,which leads to the occurrence of hydrogen evolution.Hydrogen evolution reaction caused swelling and cracking of the calcareous layer,so that the compactness and adhesion performance would decreased.The protective effect of the calcareous layer is weakened.Fluorescence microscopy experimental shows the attachment of microalgae to the surface of the material is related to the surface properties of solids,activity of microalgae and algal density.Q235 carbon steel is a highly active metal.The fast corrosion of carbon steel caused constantly updated of corrosion products on material surface,which is not conducive to the attachment of microalgae.The calcareous layer is equivalent to inorganic coating,it can promote the attachment of microalgae.Corrosion surface of metallic materials was investigated through the electron microscopy.It revealed that the interaction between the calcareous layer and microalgae can play the best protective effect of the matrix material.The existence of evident abrasion scratch on the specimens also indicates the slight corrosion is observed.In the absence of algae,part of the calcareous layer becomes loose and fall off the surface with the increase of immersion time,then lose protection to steels.Q235 carbon steel corrosion is more serious in the presence of microalgae.Microalgae affects the electrochemical behavior of metals by changing the content of dissolved oxygen in the environment.So the change in the open-circuit potential(OCP)of the metal was related to illumination.The OCP of the metal decreases with the increase of illumination time during the light gradually,the OCP being more positive with the increase of time in the absence of light.The open circuit potential showed a periodic oscillation with the change of immersion time in f/2 culture medium with microalgae in the electrochemical results.The corrosion behavior of Q235 carbon steel and calcareous samples in seawater and microalgae environment was studied.The photosynthesis of microalgae increased oxygen content in the solution.It caused cathodic oxygen depolarization reaction which can accelerate the corrosion of the metal.In the algae-free environment,the heterogeneity of calcareous layer forms the oxygen concentration cell,which can accelerates the corrosion rate and causes the local corrosion of the material.The composite membrane structure formed by the calcareous layer and biofilm is more compact and has good adhesion with the matrix,which can restrain the transfer of charge and diffusion of oxygen to the surface of the substrate,and inhibit the corrosion of metal effectively. |
PDF Full Text Request