Investigation On Anti-scale Of Polydopamine/Polytetrafluoroethylene Composite Coating

Heat exchanger plays an important role in industrial production.When the heat exchanger equipment is running,the inorganic salt in the working medium is easy to deposit on the heat exchange surface to form crystallization fouling.Heat exchange surface fouling is a poor conductor of heat,can increase the thermal resistance of heat transfer process（and sometimes even became the main thermal resistance）,scaling causes the flow in the pipeline cross-sectional area is reduced,the friction coefficient and pressure drop increases,and the corrosion of metal surfaces,serious when even lead to a broken,cause a series of economic and security issues.In most areas of China,CaCO₃ is the main crystallization fouling on the surface of heat exchanger.Therefore,the inhibition of CaCO₃ scale deposition is an important problem to be solved urgently in the industrial field.Surface modification,as an efficient,flexible and economical means of scale inhibition,has a good application prospect and important research significance.In this paper,using stainless steel commonly used as the base of heat exchange surface,a simple dip coating method was used to prepare polydopamine/polytetrafluoroethylene（PDA/PTFE）composite coating on the surface of stainless steel modified by polydopamine（PDA）to inhibit the adhesion of CaCO₃ fouling.Compared with stainless steel,the surface of PDA/PTFE composite coating has higher hydrophobicity（water contact angle is 133.5°）and lower surface free energy（11.92 m N/m）.CaCO₃ supersaturated solution prepared by Ca Cl₂ and Na HCO₃ was used for static fouling experiment to study the fouling behavior of composite coatings.At 50℃,70℃and 90℃,compared with stainless steel,the surface scale inhibition rate of the composite coating sample soaked in solution for 12 hours is 54.93%,72.73%and76.83%,respectively.During the static fouling deposition experiment,more bubbles were observed on the surface of the PDA/PTFE composite coating,and the number of bubbles increased with the increase of solution temperature,resulting in a decrease in the fouling adhesion area of CaCO₃.Therefore,the surface of PDA/PTFE composite coating has better scale inhibition performance at higher solution temperature.Tape stripping test and electrochemical corrosion test show that the PDA/PTFE composite coating has good stability and corrosion resistance.In order to obtain better PDA/PTFE composite modified surface,PTFE coating was deposited on the surface of stainless steel modified by PDA by electrophoretic deposition.The surface of the novel PDA/PTFE composite coating has micron cluster structure,and the hydrophobicity of the composite coating is significantly improved.The hydrophobicity of the composite coating is closely related to the process parameters of electrophoretic deposition.The effects of the electrophoretic time and the ratio of ethanol and water on the surface hydrophobicity are discussed.The maximum water contact angle of the prepared composite coating is 160.2±1.3°,and the surface free energy is 5.57 m N/m.Compared with stainless steel,the surface scale inhibition rate of the new composite coating sample soaked in solution for 12hours is 69.86%,75.61%and 81.36%,respectively,at 50,70 and 90℃.Combined with the stability test and electrochemical corrosion test results,the new PDA/PTFE composite coating prepared by electrophoretic deposition has significantly improved the scale inhibition performance,stability and corrosion resistance compared with the PDA/PTFE composite coating prepared by immersion coating.