Electrodeposited Nanocrystalline Nickel And Its Electrochemical Performance

In recent years, nanocrystalline materials with grain size of less than 100nm have received considerable attention. Because of the ultrafine grain size> quanta domino effect,macroscopical quanta tube effect,surface and intercrystalline volume effect, nanocrystalline materials exhibit different physical and chemical properties compared from traditional polycrystalline materials, which were called "new type materials of 21 centurys", now became a popular research field in science and industry fields. Compared with other prepared methods, electrodeposition in producing nanocrystalline material has some special advantages, such as simple equipment, low cost; preparing volume nanocrystalline materials of matels,alloys and multiplex materials easily; simple technical parameters, low temperature, etc. As a result, electrodeposition in producing nanocrystalline material has gradually received concerns.This paper is mainly researching technical parameters of direct current electrodeposition and composition of electrolyte, also researching corrosion behavior of the nanocrystalline materials, which are based on prepared nanocrystalline nickel successfully. The investigations of this paper are divided into two parts. In the first part, the effects of all kinds of compositions and electrodeposition condition on the coating are discussed. It's also put forward appropriate technical conditions and electrolyte composition. It means, nanocrystalline nickel has been produced by using Watt electrolyte and making current density above 5A/dm~2, also dominating the influence of components of electrolyte and temperature,pH,current density,churning up. In the second part, analysis and and test have been carried out by electrochemistry apparatus to investigate the cathodic polarization under the different electrodeposition conditions. Also,the polarization mechanism has been discussed. Influence of current density, temperature, additive on grain size, microstructure and magnetic performance and surface form have been researched by the X-ray diffraction(XRD) and scanning electron microscope (SEM). From the research, it's found that the current density is the important factor which affects the grain size, microstructure and magnetic performance. Current density affects the preferred orientation of the deposits. Under high current density, the deposit is prone to (200) orientation, however, under low current density, to (111) orientation. Besides, additive can change the preferred orientation of the deposit. Tafel polarization curve and Electro -chemical impedance spectroscopy have been adopted to test the corrosion action of the nanocrystalline nickel. The results of the test indicated that, in acid medium, corrosion resistance of nanocrystalline nickel is worse than ordinary nickel. because there are more atoms on the crystalline boundary in nanocrystalline, which is benefit for transmission of oxygen and erosion of the corrosive medium. However, the additive could make the deposit contained minim sulfurate, which also makes the resistance decreased.