| Once the superhydrophobic sample is immersed into water,a layer of air cushion will be formed on the solid-liquid interface.The so-formed air cushion prevents the direct contact of water and the corrosive ions?such as Cl-?in water with solid.So,the superhydrophobic surface?SHS?possesses excellent corrosion resistance.However,till now,key factors?such as hydrostatic pressure,temperature,and corrosive medium morphology?that affect the stability and the corrosion resistance of the underwater air cushion have not been studied in detail.In this thesis,SHS was fabricated by immersing the aluminum substrate sequentially into the dilute aqueous solution of hydrochloric acid,the boiling water,and the ethanolic solution of stearic acid.The effect of the hydrostatic pressure andthe temperature of the NaCl aqueous solution on the corrosion resistance of SHS was assessed by monitoring the variation in surface wettability,surface composition,and surface morphology of the superhydrophobic sample.Moreover,the corrosion behavior of superhydrophobic samples in neutral salt spray was also investigated.The main research and results are as follows:?1?Surface morphology and surface wettability.After the aluminum substrate was treated by hydrochloric acid and boiling water,the surface was uniformly coveredby a micro-step structures?generated by hydrochloric acid etching?and nano-protrusions?generated by boiling water treatment?.After modified by stearic acid?STA?,the superhydrophobic sample coded as Al-HCl-H2O-STA was fabricated with the contact angle?CA?of 166.9±2.2°and sliding angle?SA?of2°.?2?Effect of hydrostatic pressure on corrosion behavior of superhydrophobic samples.The superhydrophobic sample of Al-HCl-H2O-STA was immersed into the NaCl aqueous solution?3.5 wt%?under different hydrostatic pressure of?0 kPa,1 kPa,15 kPa?and taken out every day?24 h?to measure its surface wettability.Results showed that,under the hydrostatic pressure of0 kPa,the degradation of the superhydrophobicity was the slowest.After 30 days of immersion,the CA remained approx.146°and the SA was 32°.Under the hydrostatic pressure of 1 kPa,the CA dropped to approx.103°,and the SA was 90°.Under the hydrostatic pressure of 15 kPa,the degradation of the superhydrophobicity was the fastest.After 30 days,the CA decreased to approx.85°,and the SA was 90°.Meanwhile,the variation in surface morphology and surface composition of the sample were also characterized.As the hydrostatic pressure increases,the surface carbon content decreased gradually and the surface morphology varied more obviously.These results showed that,under higher hydrostatic pressure,the underwater air cushionon the solid-liquid interface would be squeezed out more easily,and the corrosion protection of SHS deteriorated.?3?Effect of solution temperature on corrosion behavior of superhydrophobic Samples.The superhydrophobic sample of Al-HCl-H2O-STA was immersed into the NaCl aqueous solution?3.5 wt%?with different temperatures?20?,40?,60??and taken out every day?24 h?to measure its surface wettability.Experimental results showed that,after 5 days,the Al-HCl-H2O-STA sample in NaCl aqueous solution at20?remained hydrophobic?CA=134.3±2.5°?,while the sample in NaCl aqueous solution at 40?and 60?became hydrophilic?CA decreased to 62.7±6.0°and49.8±4.8°,respectively?.Meanwhile,the surface morphology and surface composition were also characterized.As the temperature of the NaCl aqueous solution increased,the surface carbon contentdecreased gradually and the surface morphology varied more obviously.These results indicated that the STA molecules were detached from the solid surface more easily at higher temperatures.Therefore,the corrosion protection of SHS deteriorated as the temperature of the NaCl aqueous solution became higher.?4?Salt spray corrosion resistance of the superhydrophobic sample.The variation of surface wettability,surface morphology,and surface composition of the Al-HCl-H2O-STA superhydrophobic sample and the control hydrophobic samples of Al-H2O-STA?CA=135.5±2.2°?and Al-STA?CA=128.1±3.4°?exposing to neutral salt spray were monitored.The results showed that after 108 h,CA of the Al-HCl-H2O-STA sample,the Al-H2O-STA sample,and the Al-STA sample decreased to 109±3.9°,86±3.5°,and 31±4.8°,respectively.Compared with thecontrol samples of Al-H2O-STA and Al-STA,the variation in surface morphology and the decrease of surface carbon content for the Al-HCl-H2O-STA sample was smaller.These results showed that the Al-HCl-H2O-STAsuperhydrophobicsamplepossessedbettersaltspraycorrosion resistance. |
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