The electrodeposition of Zn-Ni is classified by Brenner [1] as anomalous codeposition, because zinc, the less noble metal, is preferentially deposited to nickel the more noble metal. The inhibition of H+ reduction occurs with increasing Zn ions concentration in solution. Anomalous codeposition is favored in chloride medium and inhibited in boric acid [2]
Several studies were carried out to explain this behaviour [3] in contradiction with the thermodynamic.
The nature of the anomalous codeposition has been extensively investigated. One of the explanations is the formation of the hydroxide precipitate of the more noble metal at the cathode. The hydroxide is caused by a local increase of the pH. This precipitation may suppress deposition of the noble metal. Another explanation is based on the under potential (UDP) of zinc on nickel nuclei. Ashassi and all [4] consider that anomalous codeposition is due to the slow kinetic of nickel on steel. It has been reported that the deposition of nickel needs low overpotential to create the initial nucleus and the deposit grows at low potential.
References;
[1] A.Brenner. Electrodeposition of Alloys.Vo;.2,p.194, Academic Press, New-York, 1963
[2] James P.Hoare, Journal .Electrochemical.Society. Vol 134, No.12 1987
[3]C.Karwas and T.Hepel, J.Electrochem.Soc. 135 (4) (1988) 839.
[4]H,Ashassi-Sorkhabi,A.Hagrah,N.Parvini-Ahmadi,J.Manzoori,
Surf.&Coatings technology,vol140,n0.3, pp.278-283,2001The interest of the present work is focused on the study of the simultaneous electrodeposition of Ni and Zn and anomalous phenomena that occur during the deposition. The first part is devoted to the anomalous phenomenon and its Evolution according to the ratio Ni/Zn. Indeed, we studied the effect of the composition of the solution on the composition of the electrodeposited alloys. The second part is focused on the effect of cadmium and boric acid, separately studied first and simultaneously, on the codeposition of nickel and zinc.
The electrodeposition of Zn-Ni is classified by Brenner [1] as anomalous codeposition, because zinc, the less noble metal, is preferentially deposited to nickel the more noble metal. The inhibition of H+ reduction occurs with increasing Zn ions concentration in solution. Anomalous codeposition is favored in chloride medium and inhibited in boric acid [2]
Several studies were carried out to explain this behaviour [3] in contradiction with the thermodynamic.
The nature of the anomalous codeposition has been extensively investigated. One of the explanations is the formation of the hydroxide precipitate of the more noble metal at the cathode. The hydroxide is caused by a local increase of the pH. This precipitation may suppress deposition of the noble metal. Another explanation is based on the under potential (UDP) of zinc on nickel nuclei. Ashassi and all [4] consider that anomalous codeposition is due to the slow kinetic of nickel on steel. It has been reported that the deposition of nickel needs low overpotential to create the initial nucleus and the deposit grows at low potential.
References;
[1] A.Brenner. Electrodeposition of Alloys.Vo;.2,p.194, Academic Press, New-York, 1963
[2] James P.Hoare, Journal .Electrochemical.Society. Vol 134, No.12 1987
[3]C.Karwas and T.Hepel, J.Electrochem.Soc. 135 (4) (1988) 839.
[4]H,Ashassi-Sorkhabi,A.Hagrah,N.Parvini-Ahmadi,J.Manzoori,
Surf.&Coatings technology,vol140,n0.3, pp.278-283,2001