Study On Fabrication And Properties Of Superhydrophobic Copper Surface

Copper and copper alloy materials are widely applied in electronic industry and daily life on account of their excellent properties, such as light weight, machinability, high conductivity, high thermal conductivity and malleability. So the copper is one of the non-ferrous metals that closely related to mankind. However, the copper is easily occurred and its surface is easy to frost and freeze under humidity and low temperature, and which have great threat to the stability of the electronic devices and equipment. Thus, it is quite urgent to improve the corrosion resistance and anti-icing property of the copper and its alloys, while it is a common protection step in improving the copper defect by surface treatment. In recent years, the study on the superhydrophobic surface has become one of the important topics, and lots of research has indicated that the superhydrophobic surface can prevent the water permeating into the copper substrate directly because of the strong water repellence. Consequently, the corrosion resistance, anti-icing, and self-cleaning properties can be improved.In this thesis, the simple and economic method for preparing the superhydrophobic copper-based surfaces with excellent corrosion resistance and anti-icing properties will be developed, and it has practical significance for the use of copper and its alloys under the low-temperature and moisture environment. Based on the purpose above, the superhydrophobic copper surfaces were fabricated by two simple and effective methods, and the corrosion resistance, anti-icing, and self-cleaning properties at the surfaces were discussed in detail. The main research contents are described as follows:(1) The rough structure on copper surfaces was fabricated by oxidation using Na OH and ammonium persulfate as oxidant. The effect of Na OH concentration on the morphology of CuO structure was discussed, and the obtained Cu O exhibit diverse nanostructure such as rose-like, layered hexagonal sheet, Fluff sphere-like, and nanosheets. Then the formation mechanism of CuO was analyzed, and which provided the experimental basis for the rational designing and precise controlling of the Cu O morphology.(2) The superhydrophobic copper surface was built by modifying the copper-based materials, which has been oxidized, with STA(stearic acid)-ethanol solution which contains 20 mmol/L of STA. Then the microstructure and chemical composition of the superhydrophobic surfaces were characterized by techniques of SEM and FT-IR. Results show that the long water-repellent alkyl chains(namely, C17H35COO-) are chemically bonded onto the copper surface successfully. The rough structure with ?ower-like micro-clusters forms after the STA modi?cation, and the micro ?ower-like aggregates consist of nanorods. The diameter of the nanorod is 30–50 nm, while the width of the channel is between 50 and 200 nm. These indicate that the resulting superhydrophobic copper surface has binary morphology with both micro- and nano-scale structure. Additionally, the effect of the immersion time in STA on the surface wettability was investigated, and the result indicates that the copper surface has the most excellent superhydrophobicity when the modification time in STA is 24 h. As a result, the water contact angle can reach 157.3° and the rolling angle is below 5°.(3) The second method to fabricate the superhydrophobic copper surface via modifying the CuO nano-film by 20 mmol/L of AgNO3 and 10 mmol/L of dodecyl mercaptan(DM) is developed, The surface morphology was investigated by FE-SEM, and results show that a rough structure with uniformly distributed nano-mastoid and nano-pores forms on the copper surface. In addition, the effect of the immersion time in dodecyl mercaptan on the surface wettability was investigated. The result shows that the optical immersion time is 8 h. Consequently, the superhydrophobic copper surface with a water contact angle and rolling angle of 158.3° and below 3° can be obtained.(4) The corrosion resistance of the as-prepared superhydrophobic surface, which was fabricated by STA-modified method, was investigated using dynamic polarization curve. Results show that as compared to the blank copper, the corrosion potential increases and the current density decreases for the superhydrophobic copper surface. These indicate that the corrosion resistance is improved, and the inhibitive efficiency can reach 95.2 %. The dynamic polarization curves of the copper surfaces with diverse contact angle were tested further, and the results manifest that the corrosion resistance enhances gradually with the contact angle increases.(5) The corrosion resistance and stability of the as-prepared superhydrophobic surface, which was fabricated by DM-modified method, was studied by soaking the superhydrophobic copper plate in 3.5wt% of NaCl solution. The results show that the superhydrophobicity can keep about 7 days. Then the surface corrosion resistance mechanism were analyzed by techniques as SEM, XRD, EDS, and the deduced failure reasons of the corrosion resistance is as follows: a larger quantity of air can be filled in the channels/interspace among the microstructure and low energy materials on the superhydrophobic copper plate. Consequently, the resulting copper surface can successfully prevent the penetration of the salt water into the copper substrate which effectively prevents the occurrence of corrosion. However, when soaked in 3.5wt% of Na Cl solution for a long time, the surface microstructure and the self-assembled water-repellent molecule would be destroyed by the corrosive action gradually. As a result, the copper surface would lose its superhydrophobic property.(6) The anti-icing performance of the superhydrophobic copper surface was evaluated by investigating the starting time of the water droplets freezing on the surface in low temperature. As compared to the starting time of the blank copper plate, that of the superhydrophobi c surface delays obviously at the same temperature, and the most delay time is about 16 minutes. Moreover,the delay time is reduced with the temperature decreased from-4 ℃ to-16 ℃. All these indicate that the superhydrophobic copper surface has the excellent anti-icing property. In addition, the water droplets can easily roll and carry off the powder contaminant which has been sprinkled out on the superhydrophobic copper surface. Thus, the superhydrophobic copper surface shows excellent self-cleaning performance as well.