The Study Of Preparation And Anti-corrosion Performance Of Nickel-base Multielement Alloy Coatings On Cu Substrate

Grounding gird is the guarantee of normal operation of power system. In recent years, the continuous expanding capacity of electric power system, mak es higher and higher demand on anti-corrosion performance of grounding materials. Nickel-base alloy coatings were prepared respectively on pure copper substrates by electroless plating and pulse electrodeposition to improve the anti-corrosion capability of copper grounding material in weak acid or acid soil medium. The corrosion resistance behaviors of the as-plated electroless Ni-P, Ni-Sn-P and pulse electrodeposition Ni-W-P, Ni-P coatings were investigated by potentiodynamic polarization curves, electrochemical impedance spectroscopy and accelerating corrosion indoors in 3.5 wt.% Na Cl solution at p H 5.5 and in the soil with a water content of 20 wt.% or 50 wt.% at p H 5.5.In this thesis, the anti-corrosion protection of the electroless amorphous Ni-P and Ni-Sn-P alloy coatings on copper grounding material in weak acid medium were investigated. The parameters of pulse electrodeposition of Ni-W-P alloy coating which affects the anti-corrosion performance were systematically researched and the optimum technological parameters were put forward. The effects of Mn SO₄·H₂O and La Cl_3·xH₂O on the structure, composition and anti-corrosion performance of the pulse electrodeposition of Ni-P alloy coating were also studied. This thesis provides various anti-corrosion protection coatings for copper grounding material and the main achievements are as follows:?1? The corrosion current densities and charge transfer resistances of electroless amorphous Ni-P and Ni-Sn-P alloy coating are as follows: 4.064 ?A/cm2, 1.0458 ?A/cm2, 17.54 kW cm2 and 25.14 kW cm2. The addition of Sn element can effectively reduce the porosity of coatings, and improve the corrosion resistance of the coating. The corrosion potentials of Ni-P and Ni-Sn-P alloy coating are-0.387 V and-0.281 V, which are more negative than Cu, indicating that the two electroless alloy deposits are anodic coatings compared with of Cu material. Through the electrochemical impedance spectrum test operated at room temperature and accelerating corrosion indoors which were carried in the soil with a water content of 20 wt.% at p H 5.5, we find that the anti-corrosion performance of two coatings is much better than of copper in weak acid soil.?2? The Ni-W-P alloy coatings with excellent anti-corrosion performance are manufactured by pulse electrodeposition electroforming technology. The parameters, such as bath p H, temperature?T?, average current density?im? and frequency of pulse plating?f?, which obviously influence the anti-corrosion performance were systematically studied and the optimum parameters are: p H = 2.0 ± 0.1, T = 60 ± 2?, im = 3⁵ A/dm2 and f = 600 Hz. The corrosion current density and charge transfer resistance of as-plated Ni-W-P alloy coating are 0.6434 ?A/cm2 and 67149 W cm2 in the acid Na Cl solution, while the values are 0.2126 ?A/cm2 and 120.59 kW cm2 in the soil with a water content of 50 wt.% at p H 5.5, showing more excellent anti-corrosion performance than copper in weak acid medium.?3? The effect of Mn SO₄·H₂O and rare earth La Cl_3·xH₂O on the corrosion resistance property of pulse electrodeposition Ni-P alloy deposit were stuied. Mn SO₄·H₂O can obviously increase the P content in Ni-P coating, decreasing the corrosion current density of deposit, increasing the charge transfer resistance and reducing the corrosion potential, while the deposition of Mn²⁺ does not occur. La Cl_3·xH₂O can significantly improve the corrosion resistance of pulse electrodeposition Ni-P alloy coating. With the increase of La Cl_3·xH₂O concentration, the corrosion potential of coating shifts positively. While La Cl_3·xH₂O concentration is 2.0 g/L, the corrosion resistance of the coating is the best, and the alloy deposit has the effect of cathodic protection to copper grounding grid material.