Study On The Electrochemical Fabrication And The Related Theories Of Nanostructured Ni-SiC Composite Film

Compared to the traditional polycrystal and amorphous materials, metal matrix nanocomposite thin films exhibit many excellent performances, such as unique magnetic, optical, physical chemic properties and so on. Consequently, it has a expansive applied foreground in many fields, so extensive research efforts with regard to nano-composites have been done. It is well known that deposition of electrochemical composite coatings (ECC) is not a newly developed technique and has been in continuous development since the 1970s. Meanwhile, when compared with other techniques for nanocomposite synthesis, electroplating possesses many advantages including: low cost and industrial applicability, simple operation, versatility, high production rates and so on. Therefore, the ECC technique has arosed attention of many investigators in the world.Based on the theories of "epitaxial growth" and "derivational nucleation", this dissertation tries to adopt a modification method based on traditional composite electroplating technique and a few of nano-SiC particle predecessors has been developed to fabricate the holistically nanostructured Ni-SiC films. The research not only has value in theory, but also has an expansive applied foreground.Firstly, the influences of principal technological parameters on the microstructure of eletrodeposited Ni-SiC nanocomposite film were studied. Such as: the concentration of SiC, current density, pH value, temperature, solution agitation speed and so on. We optimized a steady technics ultimately.Secondly, the microstructure of the optimized Ni-SiC composite film was characterized by scanning transmission electron microscopy (SEM), atomic force microscope (AFM) and transmission electron microscope (TEM), It can be clearly seen that the optimized Ni-SiC composite film is composed of the nanoparticles with the average grain sizes in the nanometer range, which proves that the as-obtained Ni-SiC composite film is substantially nanostructured in character.Finally, the mechanism was stuied, especially the influence of nano-SiC particles. Cyclic voltammetry (CV), chronoamperometry (CHR) and electrochemicalimpedance spectroscopy (EIS) at cathodic potential were performed. In the case of high deposition overpotential, the electroplating of Ni and Ni-SiC coating followed 3D nucleating and subsequent instantaneous grain growth mechanism. The addition of nano-SiC particles into electroplating solutions, the SiC particles will arrived at the cathode surface, and compete the active sites on the cathodic surface with nickel crystallites, which will simultaneously result in the incorporation of SiC particles into nickel matrix and the increase the cathodic polarization. Meanwhile, the engulfed SiC nanoparticles will stop the growth and congregation of existing crystalline grains mechanically due to their electric semiconductor properties, and accelerate the nucleation rate of new grains synchronously due to their high surface energy. Accordingly, the formation velocity of crystal grains will exceed the growing velocity, which results in the refining of the crystallites of Ni-SiC electrodeposits and finally in nanostructured composites.In addition, the hydrogen evolution catalytic active was primarily atuied in the 30% solution. The results show that: the electrode of Ni-SiC composite coating was better catalytic active of hydrogen evolution and was smaller resistance than the pure Ni coating. Meanwhile, with the addition of SiC, the overpotential of hydrogen evolution was augment. In a word, the nano-Ni-SiC composite film has more hydrogen evolution catalytic active and better electrochemical stability.