收稿日期：2011-11-17。收修改稿日期：2012-03-23。航空科学基金(No.20110251003)资助项目。
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通讯联系人。E -mail ：songmei_li@buaa.edu
铝合金表面用化学刻蚀和阳极氧化法制备的超疏水膜层的耐蚀性能
李松梅＊
李
彬
刘建华换轮胎需要做四轮定位吗
于
美
(北京航空航天大学材料科学与工程学院，空天材料与服役教育部重点实验室，北京
100191)
封面制作
摘要：通过化学刻蚀和阳极氧化在AA2024铝合金表面制备超疏水表面。当化学刻蚀时间超过3min 时，表面在很宽pH 值范围内显示出水静态接触角大于150°。SEM 和AFM 照片表明化学刻蚀时间决定了试样表面形貌和粗糙度。FTIR 用来研究氟硅烷(G502)与AA2024表面的结合。结果说明FAS(氟硅烷)分子与铝合金表面的三氧化二铝发生反应，并在阳极氧化膜层表面展示出优异的结合性能。超疏水表面的耐腐蚀性能通过在质量分数为3.5%的NaCl 溶液中进行动电位极化和交流阻抗(EIS)测试。电化学测试结果和等效电路模型显示出超疏水表面显著改善抗腐蚀性能。关键词：超疏水；化学刻蚀；阳极氧化；耐腐蚀中图分类号：O647.5；O614.3+1
文献标识码：A
文章编号：1001-4861(2012)08-1755-08
Corrosion Resistance of Superhydrophobic Film on Aluminum Alloy Surface
Fabricated by Chemical Etching and Anodization
LI Song -Mei ＊LI Bin LIU Jian -Hua
YU Mei
(Key Laboratory of Aerospace Materials and Performance,Ministry of Education,School of Materials Science and
Engineering,Beihang University,Beijing 100191,China )
Abstract :A superhydrophobic surface was fabricated by chemical etching and anodization on AA2024aluminum alloy.A static water contact angle of more than 150°was achieved at a wide pH value range when the surface chemical etching time was more than 3min.The SEM and AFM images showed that the surface morphology and roughness were dependent on chemical etching time.The FTIR results indicated that the FAS (fluorinated agent silane)molecules reacted with alundum on the aluminum alloy surface and the surface exhibited excellent adhesion performance on the anodization specimen.The corrosion resistance of the superhydrophobic surfaces was estimated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS)measurements in 3.5wt%NaCl aqueous solution.The electrochemical measurements and appropriate equivalent circuit models revealed that the anticorrosion performance was greatly improved by the superhydrophobic surface.
Key words :superhydrophobic;chemical etching;anodization;anticorrosion
Superhydrophobic surface with a water contact angle of more than 150°has drawn a great deal attention becau of its potential application in the industrial area and biological process [1],such as lf -clearing material [2],anti -icing coating [3],corrosion -free coating [4-5]and so on.In nature,there are many living扇贝肉的做法
things with superhydrophobic surfaces,such as lotus leaf,butterfly wing,etc.From the lotus leaf,we know that the superhydrophobicity of a material depends on not only its surface energy but also its surface morphology [1].In the past decade,many methods were developed to fabricate superhydrophobic surfaces and
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references were in the field of nano-printing[6], electrospun[7],sol-gel[8]and so on.Currently, fabrication of superhydrophobic surfaces on metal has attracted considerable rearch attention.For example, Wu and co-workers[9]obtained superhydrophobic surface asmbly of FAS(fluorinated agent silane) molecules on rough morphology created by chemical etching.Femtocond Lar ablation was ud by Kietzig[10] create roughness on steel. Wettability of the roughness steel transformed from hydrophilicity to hydrophobicity by laying the specimen in the natural environment,and reached superhydrophobicity when the lay time was over50 days.
Aluminum and its alloy have excellent physical and mechanical properties such as low density,good electromagnetism and high strength/weight ratio.Thus, they are expected to find applications in various industries such as aerospace and automobile. However,the poor corrosion resistance limits their application.Most of the corrosion occurs when the metallic matrix contacts with water and oxygen or other corrosion environment.One of the most effective corrosion protections for aluminum alloy is to treat the metal or alloy with chromium.However,chromium is toxic and harmful to the environment. Superhydrophobic surface treatment is one of the efficient strategies to protect aluminum alloy from corrosion becau the surface is water repellent and parates the metallic matrix from water and corrosion environment.In our previous study[4], superhydrophobic surface wa
s fabricated on aluminum alloy by anodization and lf-asmbly,but the method was time consuming and demanded more energy.
Here we report the preparation of superhydrophobic surface by chemical etching, anodization and lf-asmbly of FAS molecules.The static water contact angle was measured in wide pH value range.FTIR was employed to investigate the AA2024surface combination of the fluorinated agent silane(FAS)molecules.Corrosion resistance of the superhydrophobic surface was estimated by electrochemical measurements in 3.5wt%NaCl aqueous solution.
geographical
1Experimental
1.1Preparation of superhydrophobic surface on
Aluminium alloy AA2024
Aluminum alloy AA2024(composition:4.5%Cu, 1.5%Mg,0.5%Fe,0.6%Mn,0.5%Si,0.5%others and Al is the rest)with a size of60mm×40mm×3mm was ud as the substrate.The substrates were ground by emery paper(No.100,500,1000,grit sizes were 165,25,13μm,respectively)gradually,and then ultrasonically cleaned in acetone and distilled water for10min,respectively.Diluted hydrochloric acid (V HCl∶V
H
2
O
=1∶1)was ud as chemical etching solution at15℃.Chemical etching time was2~4min. Anodization process was conducted in the solution with45g·L-1sulfuric acid and10g·L-1boracic acid. The anodizing parameters were0.6A·cm-2,25℃, 20min.After anodization,the samples were immerd in100mL FAS solution containing0.6g FAS(G502, C13F12H18SiO3),40mL methanol and60mL H2O( prepared by stirring for4h at30℃)for2h at40℃.
1.2Characterization of surfaces
Water contact angles for as-prepared surfaces were estimated with optics contact angle meter (Dataphysics OCA20)bad on a ssile drop measuring method.The volume of the test water droplet was6μL.The contact angle of samples was obtained by averaging five different points.The surface morphologies of the prepared samples were estimated by scanning electron microscope(FE-SEM, Apllo300,Japan)and atomic force microscope(AFM, Veeco,MutiMode NanoscopeⅢa,USA).SE
M accelerating voltage was15kV.The AFM test was Tapping Mode and test area was15×15μm.Chemical bonds were characterized by Fourier transform infrared spectroscopy(FTIR;NEXUS-470,Nicolet). 1.3Electrochemical measurements
Potentiodynamic polarization and electrochemical impedance spectroscopy(EIS)measurements were ud to estimate the corrosion resistant of superhydrophobic surfaces.Electrochemical work
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station(Princeton Applied Rearch2273)was employed to test electrochemical measurements bad on three electrode system.All electrochemical measurements were performed in 3.5wt%NaCl aqueous solutions at room temperature.Before electrochemical measurements,the specimens were immerd in the aqueous solution for10min to obtain a stable surface.The prepared surface was ud as the working electrode with test area of 3.14cm2.A saturated calomel electrode was ud as the reference electrode and a platinum sheet was ud as the counter electrode.Potentiodynamic polarization curves were subquently measured with respect to the open circuit potential(OCP)at a scanning rate of2mV·s-1 from-0.5V to1V.Electrochemical impedance spectroscopic measurements
were conducted in the frequency ranges between10mHz and100kHz with a sinusoidal perturbation of10mV.The program Zsimpwin3.2was ud to obtain fitting parameters bad on equivalent circuit.
2Results and discussion
2.1Fabrication of Superhydrophobic surfaces
杏仁的作用
Schemes for the sample fabrication are shown in Fig.1.All of the samples were asmbled by FAS molecules.The sample only treated by chemical etching for2,3and4min is denoted as CE2,CE3, CE4,respectively,and the sample only anodized for 20min is denoted as A,and the samples treated by chemical etching for2,3and4min and anodization for20min is named as CE2A,CE3A and CE4A, respectively.Fig.2shows the water contact angle measurement on samples obtained by different treatments under wide pH value range.It can be en clearly that the surfaces anodized for20min(A)has the lowest water contact angle from90°to100°in all pH value ranges.The surface chemical etching for2 min(CE2)has water contact angle values from132°to 139°,and exhibits hydrophobic property,so is the surface treated by chemical etching for2min and by anodization for20min(CE2A).The contact angle is greater than150°if chemical etching time for the sample is over3min(CE3,CE4,CE3A and CE4A). The water contact angle has a little decrea when the pH value of water is above9.
Thus we can conclude that in the process of superhydrophobic surfaces preparation,the determining factor is chemical etching.The wettability of the surfaces changes with chemical etching time. The wettability of the surfaces becomes more hydrophobic by extending chemical etching time. Water contact angle does not show any further variations when chemical time is over3min.As shown in Fig.1,the morphology of the surfaces is altered by chemical etching.The can be obrved by FE-SEM photographs and AFM images in the next ction.The surface chemical property is changed by anodization and lf-asmbly.This will be discusd
Fig.1Schematic diagram of different process to obtain different surfaces and related typical optics contact angle
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第28卷无机化学学报
in the chemical characterization ction.
2.2Morphology of the surfaces
FE-SEM photographs and3-D top AFM images of veral samples are shown in Fig.3.(a),(b)and(c) a
re the FE-SEM photographs for sample CE2,CE3 and CE4,respectively.It can be en from Fig.3(a) that the surface of the sample by chemical etching for 2min is not destroyed totally.There exist platforms from the pretreatment in preparation and a few grooves from etching by dilute chlorhydric acid on the surfaces.As a contrast,Fig.3(b)and(c)are the images of CE3and CE4.The surfaces are completely destroyed by dilute chlorhydric acid and become rough.There are irregularly shaped particles on the
Fig.2Water contact values measured on veral samples treated by different technologies
Fig.3FE-SEM image of(a)CE2,(b)CE3,(c)CE4,(g)CE2A,(h)CE3A,(i)lf-asmbled of CE3A and3-D top AFM images of(d)CE2,(e)CE3,(f)CE4
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surfaces.Fig.3(d),(e)and(f)are the3-D top AFM images of the sample CE2,CE3and CE4, respectively.From the AFM images we know the RMS (Roughness Measurement of the Surface)of CE2,CE3 and CE4is292nm,646nm and761nm, respectively.When chemical etching time is just2 min,
the RMS is only292nm.The RMS value of CE3 is646nm,which is double of the sample CE2.The RMS value has continued to increa with chemical etching time.There is no difference between CE2 (Fig.3(a))and CE2A(Fig.3(g)),and there is also no distinction between CE3(Fig.3(b))and CE3A(Fig.3 (h)).It demonstrates that the lf-asmbly does not change the morphology of aluminum alloy surfaces when compared the Fig.3(h)and(i).
In summary,chemical etching plays an esntial role in changing morphologies and RMS.In contrast to chemical etching,anodization does not have any effects on the morphology.When chemical etching time is3min,the surface of aluminum alloy is destroyed by dilute chlorhydric acid,and the water contact angle of the surfaces reaches150°no matter the specimen is treated by anodization or not.
2.3Chemical characterization of superhydrop-
hobic职业规划怎么写
Fig.4shows the FTIR spectra of veral samples. From the whole spectrum of the sample anodized without lf-asmbly of FAS molecules(Fig.4(a)),one can e that there is only one peak at1138cm-1due to Al-O-Al stretching modes.Fig.4(b)is the spectrum of the sample lf-asmbled by FAS mole
cules on anodization AA2024,there are two peaks at1127 cm-1and1160cm-1,assigned to Si-O and Al-O-Si, respectively.There is one more peak at1245cm-1 assigned to-CF2and-CF3.The peaks demonstrate that FAS molecules are asmbled on anodized AA2024.There are no any peaks in the spectrum for the sample lf-asmbled by FAS molecules on chemical etched AA2024(CE3)as shown in Fig.4(c). It demonstrates that there are little FAS molecules on chemical etched AA2024(CE3).There are three peaks for the sample lf-asmbled by FAS molecules on chemical etched and anodized AA2024(CE3A)at 1116cm-1,1141cm-1and1241cm-1,respectively, almost the same as that of the lf-asmbled FAS molecules on anodized AA2024,which is obvious in Fig.4(b)and(d).The peak at1241cm-1is assigned to -CF2and-CF3,and the peaks at1116cm-1and1141 cm-1are assigned to Si-O and Al-O-Si,respectively, the same as that of the lf-asmbled FAS molecules on anodized AA2024.The peaks demonstrate that FAS molecules are asmbled on the sample treated with chemical etching and anodization.
It can be en from the FTIR spectra that the FAS molecules are asmbled on the specimen treated by anodizing.Anodization film on aluminum alloy is a must for lf-asmbly.Fadeev et al[11]have demonstrated that the FAS molecules reacted with the hydroxyl group on the solid surface have veral modes.Hydroxyl group is the pre-requirement for FAS molecules to react with s
olid surfaces.Takahiro Ishizaki and his co-workers[5,12]have asmbled fluoroalkylsilane molecules on magnesium alloy coated with nano-structured cerium oxide lm.The hydroxyl group on the cerium oxide is bonded with fluoroalkylsilane.Liu et al[13]ud n-tetradecanoic acid (CH3(CH2)12COOH)to asmble on the copper sheet treated with7mol·L-1HNO3for30conds to activate surfaces.The above examples demonstrate that the hydroxyl group is the most important factor in
Fig.4FTIR spectra of(a)anodized AA2024,(b)lf-
asmbly of FAS molecules on anodized AA2024,
(c)lf-asmbly of FAS molecules on chemical
etched AA2024(CE3),(d)lf-asmbly of FAS
molecules on chemical etched and anodized
AA2024(CE3A)
李松梅等：铝合金表面用化学刻蚀和阳极氧化法制备的超疏水膜层的耐蚀性能1759
