Studies on Copper-based Superhydrophobic Coating by Jet Electrodeposition
Author:Huang Da Zhi
Supervisor:tian zong jun
It is common to identify a surface with contact angles higher than 150° and roll angles less than 10°,which is superhydrophobic like the “leaflet effect” in nature.In recent years,investigations on the superhydrophobic surface and its applications in abroad aspects such as anti-icing,self-cleaning,oilwater separation,anti-corrosion coating and antibacterial coating,are receiving increasing attention.A superhydrophobic surface,in many cases,is influenced by its micro-nanostructures and low surface energy.To obtain a superhydrophobic surface on the metallic materials such as copper,iron and magnesium,various methods have been utilized by researchers.However,some inherent issues such as high-cost equipment,low efficiency and inadequate bonding strength,etc.,restrict its development and applications in industries.Jet electrodeposition is one of the electrochemical machining methods,which is able to increase current density by the application of the voltage between the workpiece(cathode)and the nozzle(anode).And thus,the electrolyte will be sprayed onto the workpiece with high deposition rate,good locality and nanocrystalline structure.These advantages enable jet electrodeposition to integrate with rapid prototyping technology,high efficiency and low-cost in an effort to achieve selective electro-deposition on the cathode surface.As a result,it is imperative to investigate the new methods and its mechanisms in preparation of the superhydrophobic coating for boosting its applications in industries.Based on the investigations of electric fields coupled with impinging jet fields,a method of numerical simulation of the flow field electric field is used to establish a jet electrodeposition process model,and the correctness of the numerical model is verified by the fixed-point jet electrodeposition test.In this paper,the model analyzes the relationship between the main parameters affecting machining and the electric field in the flow field,reveals the jet electrodeposition processing mechanism from the flow field electric field,and lays the foundation for suitable process conditions with different processing demands.Based on the understanding of the superhydrophobic theory and the guidance of the processing mechanism,this paper proposed a method of preparing the copper-based superhydrophobic coating using jet electrodeposition,and a surface with the larger contact angle and smaller roll angle could be achieved based on the optimization of this technique.The main contents of this work are listed as follows:(1)Based on the systematic analysis of jet electrodeposition,it was found that the principle difference between jet electrodeposition and conventional electrodeposition is that mass transfer changes from diffusion to strong conversion.The high-speed electrolyte,caused by the high voltage,reduced the thickness of the diffusion layer,and consequently increased the deposition effieiency.By analyzing the theory of stable electric field in the conductive medium and impinging jet flow field theory,the mechanism of selectiveness of jet electrodeposition was comprehensively studied.In details,the flow field plays a vital role in the effect of the electric field,and the electric field is limited by the impinging jet flow field,and it can only act within the jet flow field.(2)A jet electrodeposition system with automatic parameter calibration was developed,and a casting copper sample with a round-convex shape using jet electrodeposition was manufactured.And then,a numerical model of the jet electrodeposition was established by simulation software,which proofs that the electric field distribution of the fixed point jet electrodeposition was influenced by the shape of the jet field.A method for identifying the boundaries of the jet field was explored using computer numerical simulation.Compared to the experimental results,it can be revealed that the numerical model based on the 0.995 component electrolyte flow field shape is closed to the actual situation.(3)Using the established electric field model of jet electrodeposition,the parameters for jet electrodeposition including nozzle parameter,the form of the electrolyte enters the anode,the shape and location of the anode,the flow rate of the electrolyte,the distance between the nozzle and the cathode,the current density subject to the relative movement speed against with the cathode surface,the average value and the distribution of the electrolyte flow velocity,and the effects of those parameters on the flow field were comprehensively analyzed in this study.(4)Combining with the analysis of electric field of the jet electrodeposition,the feasibility of the preparation of copper-based superhydrophobic surface was explored.Compared with the surface morphology of the typical lotus leaf,the basic theory of super-hydrophobicity was discussed in depth.It was found that a copper-based superhydrophobic surfaces on copper could be obtained by controlling the main parameters such as current density,electrolyte flow rate,scanning speed,and number of scan layers,which offers the scientific knowledge for the following work.(5)By controlling the effects of the parameters including current density,scan speed and scan times on the contact angle of a pre-deposition layer prepared,the growth rate of the deposited particles on the matrix and the low surface energy modification on the sedimentary surface,were discussed in this work.Besides,it was found that a superhydrophobic surface with the contact angle of 152.6° and the rolling angle of 6.3° could be prepared using an orthogonal test,and the optimized parameters were listed as follows: the electrolyte flow rate of 1.5 L/min,the scanning speed of 12 mm/min,scan times of 1 and the current density of 950 A/dm2.The corrosion behavior of the bared copper sample and the copper sample with a superhydrophobic surface were analyzed using Tafel curves and weight loss method,and the experimental results indicated that the corrosion resistance of the surface with a superhydrophobic layer was significantly better than that of the bared copper sample..