| Grounded on their advantage of low density, high specific stiffness and strength, good machinability and castability, high thermal conductivity, and abundant availability, magnesium and its alloys are widely used in aerospace, automotive, computer, machinery, and biomaterial fields. However, magnesium alloy is highly vulnerable to the attack of corrosive media, and which seriously hinders its large-scale use.It is expected that the corrosion resistance can be improved by preparing a layer of strong water-repellent coatings at the material surfaces. Based on this, the superhydrophobic magnesium alloy surfaces are fabricated by two facile and low cost methods according to the physical and chemical properties of magnesium in this dissertation. The performance of corrosion resistance and self-cleaning of the resulting superhydrophobic magnesium alloys are investigated and discussed. The main research contents and results are described as follows:(1) A superhydrophobic magnesium alloy surface with a contact angle of 154.1° and a sliding angle of 6° is prepared successfully by hydrochloric acid etching, ammonia immersing, and long hydrophobic chains grafting. The surface wettability, microstructure and chemical structure, anti-adhesion behavior, and corrosion resistance are investigated by means of contact angle measurement, SEM observation, FT-IR analysis, anti-adhesion and electrochemical experiments, respectively. Results show that the micro- and nano-scale multiple structure presents at the magnesium alloy surface after hydrochloric acid etching and ammonia immersing, while the long hydrophobic alkyl chains are grafted onto the micro- and nano-scale surface with chemical bonds upon stearic acid modification. Just grounded on the typical surface microstructure and the chemical composition, the resultant superhydrophobic magnesium alloy surface wins the excellent anti-adhesion behavior and corrosion resistance.(2) A thin layer of superhydrophobic coating is fabricated at the magnesium alloy surface. The influence of the reaction temperature, reaction time, ethanol-water volume ratio, and the concentration of stearic acid in ethanol solution on the water contact angle is studied. Through a series of conditions change, the optimal process parameters are determined as follows: the reaction temperature and reaction time are 80 oC and 10 h, and the alcohol-water volume ratio is 1:1.4 while the stearic acid concentration is 80 mmol/L, respectively. As a result, the water contact angle at the resulting surface can reach 153.8° while the sliding angle is 6°. Results from SEM observation indicate that a sheet layer of film grows in situ from the magnesium alloy surface and which combines with the base firmly. after the hydrothermal treatment(3) The corrosion resistance of the as-prepared superhydrophobic magnesium alloy is investigated by electrochemical test and salt solution immersion, respectively. Tafel curves obtained in the electrochemical test show that the Ecorr increases and Icorr decreases, showing that the corrosion resistance of the magnesium alloy is improved by preparing the superhydrophobic coating on the magnesium alloy. In addition, the change of the contact angle, composition, phase structure, and morphology before and after the the superhydrophobic magnesium alloy are immersed with salt solution are analyzed by contact angle measurement, EDS, XRD, and SEM analysis. Results show that the superhydrophobic sample has better corrosion resistance than the blank ones.(4) The carbon powder,smoky grey, and chalk tray, which are sprinkled over the superhydrophobic magnesium surface as contaminations, can be taken away by the rolling water droplets, and which indicates that the superhydrophobic magnesium alloy surface has outstanding self-cleaning performance as well. |
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