Cathodic Polarization Of Jet Electrodeposition Of Nano-Crystalline Ni And Its Microstructure

Principle of cathodic polarization in jet electrodeposited bulk nano- crystalline Ni was studied in this paper. Influence of jet flow rate, bath composition, temperature, additive on cathodic polarization action, grain size, microstructure and magnetic performance of depositions were investigated by potentiostatic apparatus, transition electron microscope (TEM), X-ray diffraction(XRD), scanning electron microscope(SEM) and measure magnetism performance(VSM). The reason of high cathodic overpotential under high current density was probed synchronously. The experimental results show that:(1)Cathodic polarization in jet electrodeposition is controlled by electronic transfer step and liquid transmission step. High cathodic overpotential is caused by slow electrochemistry reaction of nickel ion and adsorption of hydrogen atom on cathodic surface together.(2)Cathodic overpotential increases from 1.35 V to 6.30 V(200 A/dm2) and grain size decreases from 22.6 nm to 18.9 nm when the electrolyte flow rate increases from 0.83 m/s to 5.00 m/s. With increasing Ni2+ concentration of electrolyte, cathodic overpotential decreases. Temperature increases from 40℃ to 60℃, cathodic overpotential decreases from 3.80 V to 2.95 V(150 A/dm2) and limited current density increases. Effect of additive on cathodic polarization is obvious. But this effect becomes more minute when concentration of additive exceeds 2.5 g/l. Grain size of deposits is about 8.0 nm.(3) Coercive force decreases and remanence increases when increasing jet flow rate because there is prone to (111) magnetization orientation. Coercive force and remanence increases while current density increases, because it become weaker at (111) magnetization orientation of deposits.