Treatment of the Iron Surface and its Corrosion Resistance

Transcription

1 2017 Asia-Pacific Engineering and Technology Conference (APETC 2017) ISBN: Treatment of the Iron Surface and its Corrosion Resistance Hongxin Shi, Zhijie Zhou, Haimin Shen and Hongke Wu ABSTRACT Preparation and corrosion resistance of iron plate with micro-nano-structure were investigated. A clean iron plate was etched with a mixture of FeCl 3, H 2 O, hydrochloric acid, H 2 O 2 and H 3 PO 4 to form a super hydrophilic surface which was treated with fatty acid solution to form a micro-nano-structure surface on which the water contact angle was about 147. The super hydrophilic surface was treated with 3-aminopropyltriethoxysilane solution and then fatty acid solution (test plate) to turn to a super hydrophobic surface and the water contact angle was greater than 150. This test plate coated with alkyd vamish exhibited better corrosion resistance to H 2 SO 4 than blank iron plate. INTRODUCTION Wettability is an important performance of solid surface and depends on its chemical composite as well as microcosmic appearance [1, 2]. The wettability of solid surface is expressed as contact angle (θ) of water on the surface. When θ< 90, the solid surface is deemed to hydrophilic surface and, especially, super-hydrophilic surface if θ<10 ; When θ>90, the solid surface is deemed to hydrophobic surface and, especially, super-hydrophobic surface if θ > 150. Complex wettability of solid surface is more useful than sole-wettability. A super hydrophobic and super lipophilic surface can separate oil from oil-water mixture simply and effectively, and avoid pollution in the process of oil-water separation [3, 4]. A super hydrophobic and super oleophobic surface can realize self-cleaning to oil and water, which resolves the cleaning problem of out wall or window glass of tall building, satellite antenna, solar panel without any problems of high cost, pollution and safety[5,6]. Super hydrophobic material is applied to watercraft surface to form a thin layer of air between surface and water, which can greatly reduce surface friction and increase voyage speed. Super hydrophobic surfaces possessing corrosion resistance[7,8], self-cleaning [9, 10], anti-icing[11,12], separation of oil-water mixture[13,14] and fluid drag Hongxin Shi a, Zhijie Zhou b, Haimin Shen c and Hongke Wu d Zhejiang University of Technology, College of Chemical Engineering, Hangzhou , China a shihxin@zjut.edu.cn, b zhijie0916@sina.com, d wuhongke@zjut.edu.cnreduction [15] c haimshen@zjut.edu.cn, 385

2 are used widely in industry and daily life, which excite us to research preparation of super-hydrophobic surface. Preparation of super-hydrophobic surface includes etching[16,17], aggradation[4,18], sol-gel[19,20], template[21,22] and layer-by-layer self-assemble[23,24]. Herein, we prepare super- hydrophobic surface on iron plate by etching iron surface, treating with fatty acids. The iron plate prepared was covered with paint and displayed good anti-corrosion to H 2 SO 4. MATERIALS AND METHOD Materials Hydrochloric acid (AR, Hangzhou Shuanglin Chem. Reagent Fact.), hydrogen peroxide (H 2 O 2, AR ) and phosphoric acid ( H 3 PO 4, AR) (Shanghai Ling Feng Chem. Reagent Co., Ltd.], iron trichloride ( FeCl 3,CR) and Lauric acid ( C 11 H 23 - COOH, CR )(Sinopharm Chem. Reagent Co., Ltd.), stearic acid (C 18 H 35 COOH, AR, Wenzhou chem. materials fact.), ethanol (C 2 H 5 OH, AR, Anhui Ante food Co., Ltd), palmitic acid (C 15 H 31 COOH, AR, Shanghai Wulian Chem. Fact. Co., Ltd), sodium hydroxide (NaOH, AR, Xilong Chem. Co., Ltd.), 3-amironpropyltriethoxysilane (APTES, CR, Aladdin), Myristic acid (AR, Huadong Medicine Group Co, Ltd.], alkyd vamish (Hangzhou Paint Co.,Ltd.), iron plates (Q235, 0.5 mm, Jiaxing Deli Co., Ltd.). Field emission scanning electron microscope (S-4700, Hitachi Ltd.), Contact angle measuring instrument (DSA 100S, KRÜSS). Cleaning Iron Plate Surface Firstly, an iron plate was dipped into 50 ml NaOH aqueous solution (2.50 mol/l) at room temperature for 30 minutes to wipe off the grease and then washed with the deionized water. Secondly, the iron plate was dipped into 50 ml HCl aqueous solution (2.75 mol/l) in room temperature for 30 minutes to wipe off the oxide and then washed with the deionized water. Etching the Iron Plate The cleaned iron plate was dipped into a mixture of 8.0 g FeCl 3, 2 ml HCl, 2 ml H 2 O 2 and 2 ml H 3 PO 4 at room temperature for 20 minutes and then washed with deionized water and dried with hot air at room temperature. Preparation of the Super-hydrophobic Iron Surface Modifying with Fatty Acid The cleaned and etched iron plate was dipped in 15mmol/L ethanol solution of fatty acid at 50 for 3 hours, rinsed with deionized water and dried with hot air at room temperature. Modifying with silane coupling agent and fatty acid Firstly, the cleaned and etched iron plate was dipped in 15mmol/L ethanol solution of APTES at 50 for 3hours, and was washed with deionized water. Secondly, this iron plate was dipped in15mmol/l ethanol solution of fatty acid at 50 for 3 hours, rinsed with deionized water and dried with hot air at room temperature. 386

3 Measuring the Water Contact Angle The contact angle was measured with 8μL droplet of deionized water at room temperature using a protractor eyepiece of DSA100S. At least three parallel measurements were made for each iron plate, and the three places were chosen at random. The three contact angles gave the average contact angle. Anti-corrosion Tests The iron plate with super-hydrophobic iron surface was coated by alkyd varnish and the paint layer was about 100 μm. After being dried in oven at 80 for 8 hours, the iron plate was cooled to room temperature, and then dipped in aqueous solution of H 2 SO 4 at same temperature. The appearance and change of the coating layer were observed by eyes in every 5 days. RESULTS AND DISCUSSION Micro-nano-structure of Iron Surface The iron plate was washed by 10% aqueous solution of NaOH and water at room temperature, and then was etched in a mixture of 8.0 g FeCl 3, 30 ml H 2 O, and 2 ml hydrochloric acid, 2 ml H 2 O 2 and 2 ml H 3 PO 4 for 30 minutes. SEM image of the iron surface etched was shown in Fig. 1. Fig. 1(b) was a local enlargement in Fig 1(a). It was very clear that there were a great number of protrusions in microstructure on the iron surface. These protrusions were the prerequisite to build a super hydrophobic surface. a Figure 1. SEM micrograph of the etched iron surface. b The etched iron plate was washed by water, treated by palmitic acid solution. The SEM image of the iron surface treated was shown in Figure 2. Fig. 2(b) was a local enlargement in Fig. 2(a). There was some nano-structure on the micro-structure protrusions of the treated iron surface. These micro-nano-structures on the iron surface endowed it with super hydrophobic performance. 387

4 a Figure 1. SEM micrograph of the iron surface etched. b Water Contact Angle on the Iron Surface Treated The effects of fatty acids on the water contact angle on the treated iron surface were investigated. Table 1 revealed that the iron surface was super hydrophilic after etching and the water contact angle was only 5. After being treated with fatty acids, the water contact angles on the iron surface increased greatly, and reached to about 147. There were no effects of kinds of fatty acids on the water contact angles. The carbon train of stearic acid (C18)is the longest, the lauric acid (C12) is the shortest,and the length of carbon train affected the micro-nano-structure of iron surface slightly, so the differences among their water contact angle are very small. TABLE 1. WATER CONTACT ANGLES ON THE IRON SURFACE TREATED BY FATTY ACIDS. Fatty acid carbon train Contact angle [ ] no 5 Lauric acid C Myristic acid C Palmitic acid C Stearic acid C The water contact angles on iron surface treated with fatty acids was small than 150 and not reached the level of super hydrophobic surface. If the iron plate etched was treated with APTES and then with fatty acids, the water contact angles on the iron surface increased over 150. But, from the result of Table 2, the differences of water contact angles for the fatty acids were not distinct either. 388

5 TABLE 2. WATER CONTACT ANGLES ON THE IRON SURFACE TREATED BY FATTY ACIDS. Fatty acid carbon train Contact angle[ ] Lauric acid C Myristic acid C Palmitic acid C Stearic acid C Corrosion Resistance The iron surface etched and treated with APTES and palmitic acid (or test plate) was coated with alkyd varnish, after being dried in hot air, it was dipped in aqueous solution of H 2 SO 4 at room temperature. A clean iron plate without etching and treating (or blank plate) was coated and dried in the same condition The appearance of coating layers were observed and the results were shown in Table 3. Coating layers of alkyd varnish on the iron plate possessed certain corrosion resistance to aqueous solution of H 2 SO 4; they had no change during first 5 days. The concentration of H 2 SO 4 was an important factor to corrosion. For the blank plate, the time when the coating layer began to raise and the time when it broken off from the iron plate were at 25th day and at 30th day in 10% H 2 SO 4 and were at 10th day and 15th day in 20% H 2 SO 4, respectively. But for the test plate, they were 30th day and 40th day in 10% H 2 SO 4 and were 15th day and 25th day in 20% H 2 SO 4, respectively. The treatment of iron surface by etching and ornament with APTES and palmitic acids took a key role in corrosion resistance to aqueous solution of H 2 SO 4. There is a great number of hydroxyl groups on the surface of iron plate etched, APTES can easily react with these OH groups, 3-aminopropyl was linked to iron surface by Si-O bind. Alkaline aminopropyl could combine closely with acidic fatty acid to form close self-assembled monolayers which was hydrophobic. Aliphatic chain of the fatty acid has affinity with alkyd vamish (paint), so iron surface combined with paint more tight by this way than that paint coated iron surface directly and exhibited better corrosion resistance to H 2 SO 4. TABLE 3. CORROSION RESISTANCE OF IRON PLATE. H 2 SO 4 /% Time/day Blank plate Test plate Blank plate Test plate : -no change, -coating layer begin to raise, - part of coating layer broken off, -all coating layer broken off 389

6 SUMMARY A clean iron plate was etched with a mixture of 8.0 g FeCl 3, 30 ml H 2 O, 2 ml hydrochloric acid, 2 ml H 2 O 2 and 2 ml H 3 PO 4 to form a micro-structure and hydrophile surface on which the water contact angle was about 5. The etched iron plate was treated with fatty acid solution and formed a micro-nano-structure surface on which the water contact angle was about 147. But the etched iron plate was treated with APTES solution and then fatty acid solution (test plate), the micronano-structure surface formed was super hydrophobic and the water contact angle was greater than 150. This test plate was coated with alkyd varnish (paint) and exhibited better corrosion resistance to H 2 SO 4 than blank plate. ACKNOWLEDGMENTS This work was supported by the Research Fund of the Department of Science and Technology of Zhejiang Province ( 2011R ). REFERENCES [1] Feng L, Li S, Li Y, et al. Super hydrophobic surfaces: from natural to artificial [J]. Advanced materials, 2002, 14(24): [2] Patankar N A. Mimicking the lotus effect: influence of double roughness structures and slender pillars [J]. Langmuir, 2004, 20(19): [3] Wu J, Chen J, Qasim K, et al. A hierarchical mesh film with super hydrophobic and superoleophilic properties for oil and water separation [J]. Journal of Chemical Technology and Biotechnology, 2012, 87(3): [4] Feng L, Zhang Z, Mai Z, et al. A super hydrophobic and super oleophilic coating mesh film for the separation of oil and water [J]. Angewandte Chemie International Edition, 2004, 43(15): [5] Zhang H, Lamb R, Lewis J. Engineering nanoscale roughness on hydrophobic surface preliminary assessment of fouling behaviour[j]. Science and Technology of Advanced Materials, 2005, 6(3): [6] Zheng Z, Gu Z, Huo R, et al. Fabrication of self-cleaning poly (vinylidene fluoride) membrane with micro/nanoscaled two tier roughness [J]. Journal of Applied Polymer Science, 2011, 122(2): [7] Yin B, Fang L, Hu J, et al. Preparation and properties of super-hydrophobic coating on magnesium alloy [J]. Applied surface science, 2010, 257(5): [8] Zang D, Zhu R, Wu C, et al. Fabrication of stable superhydrophobic surface with improved anticorrosion property on magnesium alloy[j]. Scripta Materialia, 2013, 69(8): [9] Nishimoto S, Bhushan B. Bioinspired self-cleaning surfaces with superhydrophobicity, superoleophobicity, and superhydrophilicity [J]. Rsc Advances, 2013, 3(3): [10] Kota A K, Li Y, Mabry J M, et al. Hierarchically structured superoleophobic surfaces with ultralow contact angle hysteresis [J]. Advanced Materials, 2012, 24(43): [11] Cao L, Jones A K, Sikka V K, et al. Anti-icing superhydrophobic coatings[j]. Langmuir, 2009, 25(21): [12] Kako T, Nakajima A, Irie H, et al. Adhesion and sliding of wet snow on a super-hydrophobic surface with hydrophilic channels [J]. Journal of Materials Science, 2004, 39(2): [13] Yao X, Song Y, Jiang L. Applications of Bio Inspired Special Wettable Surfaces [J]. Advanced Materials, 2011, 23(6): [14] Chu Q, Liang J, Hao J. Facile fabrication of a robust super-hydrophobic surface on magnesium alloy [J]. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2014, 443: [15] Gau H, Herminghaus S, Lenz P, et al. Liquid morphologies on structured surfaces: from microchannels to microchips[j]. Science, 1999, 283(5398): [16] Wang S, Guo X, Xie Y, et al. Preparation of superhydrophobic silica film on Mg Nd Zn Zr 390

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