【作者】 牛朝霞；

【导师】 曹楚南； 张昭；

【作者基本信息】 浙江大学 ， 物理化学， 2006， 硕士

【摘要】 相对于传统的多晶和非晶薄膜材料,纳米结构薄膜具有优异的磁性、光学、物理、化学和电化学特性,因而在诸多领域中具有广阔的应用前景,所以近年来,关于纳米薄膜做了很多研究。复合电镀技术起源于二十世纪七十年代,由于电化学方法成本低、易实现工业化、操作简单、效率高等等,相对于纳米结构薄膜的其它制备方法(如:sol-gel)具有独特之处,而且复合电镀技术已经在材料制备中得到了广泛的应用。因此,具有优异性能的纳米结构复合薄膜的电沉积研究,必将引起了国内外广大科技工作者的普遍关注。 本研究拟基于电沉积过程中的“外延生长”和“诱导成核”等理论,采用电化学方法和纳米晶前驱诱导物来制备纳米晶薄膜材料,开拓一条全新的纳米材料制备方法。该研究具有重要的理论价值和广阔的应用前景。 论文首先对纳米复合电沉积的工艺进行了优化,主要从以下几个因素入手:SiC浓度、电流密度、pH值、电镀温度、搅拌方式及强度、添加剂的种类及含量等等。最终优化出一套稳定、可靠的工艺。 其次,对在优化好的条件下制备的纳米复合薄膜进行了一系列的表征,如SEM、AFM、TEM、XRD等等,结果表明,复合薄膜均匀致密,粒子大小为纳米级的,证明了上述工艺的可靠性。 最后,我们对复合电沉积的机理进行了研究,特别是纳米粒子对晶粒成核和生长机理的影响。我们主要通过一些电化学测试手段,如循环伏安、计时安培和电化学阻抗等等。结果表明:在较高的阴极过电势条件下,Ni和Ni-SiC薄膜均遵循扩散控制下的3D瞬时“成核/生长”机制。另外,由于纳米SiC粒子在阴极表面的吸附作用所引起的阴极极化增大了阴极表面Ni微晶的成核数目,同时由于纳米SiC粒子在镀层中的夹杂作用所引起的空间位阻效应抑制了Ni晶粒的长大。二者的共同作用导致了Ni-SiC复合薄膜晶粒的细化和最优条件下的整体纳米结构复合薄膜。 同时,还初步探讨了纳米Ni-SiC复合薄膜在30wt.%KOH溶液中的电催化析氢性能,发现复合薄膜较纯Ni薄膜具有较低的析氢过电势和较小的析氢反应电阻,即具有较好的电催化析氢特性。同时纳米结构Ni-SiC复合薄膜具有较高的电化学稳定性。在实验条件下,所有Ni-SiC复合薄膜均较纯Ni镀层具有较高更多还原

【Abstract】 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.更多还原