雙層無電鍍鈷鎳之抗蝕研究

The Study of Corrosion Resistance of Electroless Cobalt-Nickel Double Layer

本實驗以次磷酸鈉為還原劑，低碳鋼片為底材，被覆無電鍍鎳磷、鈷磷雙層合金鍍層，根據在3.5%氯化鈉溶液中的電化學分析、浸漬實驗、鹽霧實驗的腐蝕測試結果，發現無電鍍鎳合金層相對於無電鍍鈷合金層較鈍性，無電鍍鎳磷的腐蝕電位Ecorr= -446mV，而無電鍍鈷磷腐蝕電位Ecorr= -585 mV；以較鈍性之無電鍍鎳合金層為下層，較活性之鈷合金層為上層，則無電鍍鈷合金層具有犧牲保護作用，可保護下層金屬；若以較活性之鈷合金層為下層，較鈍性之無電鍍鎳合金層為上層，則無犧牲保護作用，且鈷磷為上層而鎳磷為下層的防蝕效果應較上層為無電鍍鎳，下層為無電鍍鈷佳；以光學顯微鏡觀察腐蝕形態無電鍍鎳層的腐蝕形態為孔蝕，無電鍍鈷層為均勻腐蝕。

Double layer of Ni-P and Co-P coatings was prepared by electroless plating with sodium hypophosphite as reducing agent. Based upon corrosion testing results of electrochemical analysis, dipping test, and salt-spray test, Ni-P coating is more inert than Co-P coating. Corrosion potentials are Ecorr=-446mV, and Ecorr=-585mV for Ni-P and Co-P coatings, respectively. Double layer with Co-P coating as outer layer and Ni-P coating as inner layer is more corrosion-resistant. The morphology of corrosion pattern was investigated by optical microscopy and closely related to the rearrangement order of coatings in the double layer.