Experimental Study On The Process Of Preparing Superhydrophobic Nickel Coating By Scanning Jet Electrodeposition

The superhydrophobic surface has special wetting properties and can be applied in many fields such as self-cleaning,anti-corrosion,biological adhesion mitigation and fluid drag reduction.Surface wettability is controlled by surface free energy and surface roughness.Constructing a suitable surface roughness is the basis for the preparation of superhydrophobic surfaces.Electrodeposition has unique advantages in the preparation of superhydrophobic surfaces,as it is a simple and fast process,with high repeatability,low cost,and it has the possibility to obtain various surface morphologies.Jet electrodeposition is a selective deposition process with the advantages of flexibility and high efficiency.In this paper,a nickel coating with micro-nano hierarchical structure was prepared by anode scanning jet electrodeposition.After a week of natural hydrophobization in the air,a surface with excellent superhydrophobic properties was obtained.The research proposed a new preparation method for superhydrophobic surface,and revealed the mechanism of coating growth and the mechanism of surface wettability transition.The main contents are as follows:（1）The desktop-level anode scanning jet electrodeposition machine was designed and built.Compared with other jet electrodeposition machines,this machine is easier to operate and maintain,and has a wider range of applications.（2）The effects of additive concentration,average current density and number of scans were investigated.The rough cluster structure was formed on the coating surface with the addition of NH₄Cl.The size and density of clusters increased with the increase of NH₄Cl concentration,the increase of the number of scans and the increase of average current density.The role of NH₄⁺was to stabilize the pH of the cathode surface,enhance the hydrogen evolution reaction,reduce the nucleation probability of metal deposition,promote the longitudinal growth of the crystal,and make the coating rough.On this basis,the additive concentration and processing parameters to fabricate the superhydrophobic nickel coating were determined:the NH₄Cl addition amount was 120g/L,the average current density was 30A/dm²,and the number of scans was 400 times.（3）The growth process of the coating was studied.Due to the presence of NH₄⁺and the high instability of the deposition interface under jet conditions,as the deposition continued,protrusions formed on the surface and the surface roughness increased.Under the"tip effect"and its shielding effect,the coating growth was changed from the previous surface growth to the dendrite growth of the protruding region.Many cauliflower-like clusters with micro-nano hierarchical structure were formed on the coating surface.The entire coating can be divided into two parts:a dense nickel coating on the bottom and a coarse cluster structure thereon.（4）The mechanism of the wettability transition of the coating surface was investigated by detecting the surface chemical composition.The newly prepared coating was super-hydrophilic and was converted to superhydrophobic after exposing in air for one week.The spontaneous adsorption of airborne organic hydrocarbons on the surface was responsible for the change of wetting properties.These organics reduced the surface free energy of the coating and interacted with the coarse structure of the coating,making the coating surface a low adhesion superhydrophobic surface in accordance with the Cassie-Baxter model.（5）The properties of the prepared superhydrophobic nickel coating were verified from a number of perspectives.After exposing in the air for one week,the contact angle of a 6μL water droplet on the surface reached 155.4°,and the rolling angle was 6.5°.After placing at 200°C for 3hours,the coating still retained superhydrophobic.The superhydrophobic nickel coating had better corrosion resistance than the ordinary bright nickel coating prepared by jet electrodeposition.