Electrodeposition Behavior of Zn–Co Alloys from an Alkaline Zincate Solution Containing Triethanolamine

Abstract

Electrodeposition behavior of Zn-Co alloys was investigated at current densities of 2-500 A·m −2 and a charge of 5 × 10 4 C·m −2 at 308 K in an unagitated zincate solution containing triethanolamine, which forms a stable complex with Co 2+ ions. At current densities lower than 5 A·m −2 , the Zn-Co alloys exhibited normal co-deposition behavior, with the electrochemically more noble Co being preferentially deposited. By contrast, at current densities higher than 6 A·m −2 , they exhibited anomalous co-deposition behavior, with the electrochemically less noble Zn being preferentially deposited. The current efficiency for Zn-Co alloy deposition was low (about 20%) in the normal co-deposition region, while it was 95% in the anomalous co-deposition region. Also, in the anomalous co-deposition region, the partial polarization curves for Co deposition and H2 evolution were significantly shifted to the less noble direction by the coexistence of Zn 2+ ions, suggesting the formation of an inhibitor species that results from the presence of Zn 2+ ions in the cathode layer. On the other hand, in the normal co-deposition region, the underpotential deposition of Zn apparently occured simultaneously with Co deposition. Zn-Co alloys are composed of stable intermetallic compounds CoZn13 and Co5Zn21; therefore, the activity coefficient of Zn in the deposits appears to decrease remarkably.

光沢剤を含むアルカリジンケート浴から電析したZn-Ni合金皮膜の耐食性

“…Zn − Ni 合金めっき鋼板は，Zn めっき鋼板に比べ耐食性 に優れているため，自動車部品，家庭電化製品，建材用部 品などに幅広く使用されている [1][2][3][4][5][6][7][8] 。Zn − Ni 合金めっき は，硫酸塩浴，塩化物浴から行われることが多いが，小物 部品等に対する均一電着性の観点からは，ジンケート浴を 用いた方が望ましい [9][10][11][12][13][14][15][16][17][18][19]…”

Effects of Electrolysis Conditions on the Formation of Electrodeposited Invar Fe–Ni Alloys with Low Thermal Expansion

“…It is well known that iron-group metals such as Fe, Co, and Ni inherently do not begin to deposit at their equilibrium potential and require an overpotential for deposition. [23][24][25][26][27][28] The minimum overpotential required to initiate the deposition of iron-group metal results from the rate-determining step of the multi-step reduction of iron-group metal ions. The series of reactions below have been proposed as the deposition process for iron-group metals.…”

Corrosion Resistance of Zn–Ni Alloy Films Electroplated in Alkaline Zincate Solutions Containing a Brightener

“…[1][2][3][4][5][6][7][8] Zn-Ni alloy electrodeposition is generally performed in sulfate and chloride solutions, but the zincate solution is a desirable alternative for electrodeposition on small components. [9][10][11][12][13][14][15][16][17][18][19] In Zn-Ni alloy deposition in a zincate solution, the brightener is generally added to the solution. The relationship between the final product's appearance quality and the brightener has been studied, [20][21][22] but the effect of the brightener in solution on the corrosion resistance of deposited films has not been extensively studied.…”