| As one of the most widely used metal materials in engineering,it is often used in aviation,construction,automobile and many other fields.Its importance in industry is self-evident.The corrosion of mild steel causes not only huge economic losses,but also brings disastrous safety problems every year.The most straightforward and effective anti-corrosion method for metals is the application of protective layer,which can isolate metals from direct contacting with outside.However,most of the protective layer is difficult to protect substrate for a long time,especially the corrosive liquid wetting the protective layer,the failure process of the protective layer will be accelerated.Inspired by the superhydrophobic property of lotus leaf surface,if the superhydrophobic structure can be constructed on metal surface,then modified with low surface energy substance,the actual contact area between the liquid and the protective layer can be greatly reduced.As a result,the metal corrosion rate can be retarded.Nowadays,researchers have applied the superhydrophobic surface for corrosion protection of metals and got some achievements.Nonetheless,most of the construction process of superhydrophobic structures is complex,and it exist many other shortcomings such as it need expensive processing equipment or with harsh construction conditions,which make it difficult to achieve large-scale industrial production.Besides,many researchers did not make deep analysis of the anti-corrosion mechanism,long-term protection performance and the relationship between micro structure and wettability.To addressing the above problems,we conducted the following researches:Took advantage of the facile electrodeposition method to fabricate superhydrophobic nickel(Ni)coating on mild steel surface.The influence of current density on the micro structure and wettability was systematically investigated;the relationship between micro structure and wettability was clarified.Besides,the corrosion resistance and long-term protection performance of the superhydrophobic coating were deeply studied.Moreover,the anti-corrosion mechanism of the superhydrophobic coating was revealed based on the above results.The results showed that the current density has a vital influence on the micro structure of coatings,and directly affect coatings'wettability and corrosion resistance.When the current density is 6 A/dm2,the coating exhibited a“starfish”structure,after modification with myristic acid,the contact angle could be up to 152.6±1.1°,and the sliding angle showed a very low value about 5.5±0.5°,the the corrosion current density of this coating is about 2.022×10-7A/dm2.Furthermore,after being soaked in 3.5wt.%Na Cl solution for 14 days,this superhydrophobic coating can still protect low carbon steel very well,showed an excellent long-term corrosion protection performance.On account of the corrosion resistance of Zn-Ni coating is superior than that of pure Ni coating in.In this work,the superhydrophobic Zn-Ni coating with hierarchical micro-nano structure was constructed on the surface of mild steel by electrodeposition and alkali etching.The effect of etching time on the micro structure and wettability were analyzed in detail.Moreover,the relationship between the micro structure and the wettability as well as the adhesion force was specified,the coatings'corrosion resistance was analyzed by electrochemical method,and of the anti-corrosion mechanism of these coatings was analyzed by equivalent circuit models.At last,the application of these coatings in self-cleaning and micro-fluid no-loss transmission was studied according to the different wettability of coatings.The results showed that the modified rough Zn-Ni coatings were all displayed large contact angles.And with the extension of etching time,the adhesion force between coatings and water droplets become weaken.Meanwhile,the sliding angles of coatings become smaller.With the etching time of 20 min,the super hydrophobic coating owned a corrosion current density of 2.748×10-9A/dm2,which is lower than that of single superhydrophobic Ni coating for two orders of magnitude.A semi-closed porous superhydrophobic surface of Zn-Ni-Co coating was developed by electrodeposition combined with chemical replacement.Besides,a porous superhydrophobic surface of Ni O/Zn O composite surface and superhydrophobic Zn O nanorods were prepared by thermal decomposition and hydrothermal synthesis respectively.The durability of the semi-closed porous superhydrophobic surface and the superhydrophobic surface with an open system were analyzed and compared.In the meantime,the corrosion resistance and long-term protection performance of the novel Zn-Ni-Co superhydrophobic surface were also investigated.The results showed after replacement for 10 min,the obtained superhydrophobic Zn-Ni-Co surface showed not only well corrosion resistance,but also excellent wear resistance.Based on the existence of metal porous structure,air can be stored very well.Thus,it could maintain the superhydrophobic performance for a longer time.Depositing chromium(Cr)coatings on the above three kind of surfaces which with different micro-nano structures,realizing controllable construction of coating from single layer to multi-layer.Then the wettability,hardness,mechanical stability and corrosion resistance of each coatings before and after chromium deposition were analyzed deeply.The results showed that when deposited Cr on Ni coatings for 20 s,the superhydrophobicity can be enhanced by almost keeping the original morphology,and the corrosion current density can be lower to 2.535×10-8A/cm2.Meanwhile,the hardness and wear resistance were both improved after deposited with Cr.When deposited Cr on superhydrophobic Zn-Ni coatings,the contact angle and the corrosion resistance of coatings were both decreased.On the contrary,the hardness of coating was increased by about 100 HV after deposited Cr for 30 s,and the wear resistance was also had a significant improvement.When Cr was deposited on the surface of superhydrophobic Zn-Ni-Co coating,Cr was first grew on those porous structure and thus the roughness of coating decreased,and the superhydrophobicity was also lost.However,due to the existence of Cr layer,the self-corrosion current density was still lower than that of the superhydrophobic Zn-Ni-Co coating for about one order of magnitude.And the hardness and wear resistance of coatings were both enhanced with different degrees.The slippery surface was prepared by infusing lubricant on the surface of the fluorosilane modified Zn-Ni-Co porous coating.The results showed that the slippery surface had better stability and corrosion resistance than superhydrophobic Zn-Ni-Co coating.In addition,after physical damaged by knife,the slippery surface could self-healed in a short time and continuously protect substrate from damaging.After that,a porous phosphating film was prepared on the surface of Zn-Ni coating,which was also modified by fluorosilane and filled with lubricant.Due to the perfect combination of superhydrophobic phosphating surface and lubricant,the corrosion current density of the slippery surface was as low as 1.927×10-11A/cm2,showed very excellent anti-corrosion performance.The slippery property can maintained even after being soaked in 3.5 wt.%Na Cl solution for 6 weeks,showed an outstanding stability.And the corrosion current density of this surface is 1.373×10-10A/cm2,demonstrated and long-term and efficient anti-corrosion performance.In this thesis,it is innovative for the design and fabrication of several superhydrophobic structures,the results provide important scientific basis and theoretical guidance for anticorrosion of low carbon steel and other metals..In addition,the slippery surface which was prepared based on superhydrophobic structure provides a reference for the sustainable corrosion protection of metals. |
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