Galvanic Deposition of Gold and Palladium on Magnesium by the Method of Substitution
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GALVANIC DEPOSITION OF GOLD AND PALLADIUM ON MAGNESIUM BY THE METHOD OF SUBSTITUTION O. Ya. Dobrovets’ka,1, 2 O. I. Kuntyi,1 G. I. Zozulya,1 I. V. Saldan,3 and O. V. Reshetnyak3 We study the deposition of Au and Au–Pd onto the surface of a rotating magnesium disk by the galvanic substitution in dimethylformamide solutions of 0.004 M HAuCl 4 and 0.004 M HAuCl 4 with (0.004–0.01) M PdCl 2 at 20–60°C. The formation of films made of Au or Au–Pd particles with sizes of 0.3–1.0 µm or 0.1–0.3 µm, respectively, on the magnesium surface is demonstrated. The predominant reduction of Au during the codeposition of gold and palladium is revealed. A possibility of controlling the content of the metal in Au–Pd bimetallic systems is shown in practice. Keywords: galvanic substitution, magnesium, gold, palladium, nonaqueous medium.
In recent years, the possibility of fixation of catalytically active metals on the surfaces of metals reducers by the method of galvanic substitution is regarded as one of the promising methods in the production of new materials [1–6]. This method is characterized by the simplicity of realization and a broad range of metal/substrate combinations. Moreover, it enables us to deposit both individual metals [1–4] and their binary systems [5, 6]. The galvanic substitution is realized according to the electrochemical mechanism described by the following general reaction:
mM1n+ + nM 2 ↔ mM1 + nM 2m+ .
(1)
The deposits of a metal M1 with more positive standard potential are formed on microcathodes due to the presence of “generated” electrons from a metal M 2 . The electromotive force of process (1) depends on the difference between the standard electrode potentials of M1 and M 2 (ΔE) . Hence, the choice of the pair M 2 and M1 determined by the value of ΔE 0 , i.e.,
0 0 ΔE 0 = EM − EM , n+ m+ /M /M 1
1
2
2
(2)
and the composition of the electrolyte are the principal factors affecting the entire process of galvanic substitution (1). As a rule, M1 are noble metals: Au [1, 5], Ag [2, 3, 5], and Pd [4–6] characterized by high values of the
0 ). In practice, their deposition on the surface of M 2 can be realized by standard electrode potentials ( EM n+ /M 1
1
the galvanic substitution of gold with silver [1] or silicon [5], silver with germanium [3], and palladium with magnesium [4]. In view of the high interest in the protective and functional coatings of magnesium and its al-
1 2 3
National University “L’vivs’ka Politekhnika”, Lviv, Ukraine. Corresponding author; e-mail: [email protected]. Franko Lviv National University, Lviv, Ukraine.
Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 51, No. 3, pp. 112–116, May–June, 2015. Original article submitted December 17, 2014. 418
1068-820X/15/5103–0418
© 2015
Springer Science+Business Media New York
GALVANIC DEPOSITION OF GOLD AND PALLADIUM ON MAGNESIUM BY THE METHOD OF SUBSTITUTION
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loys [7], the modification of the surface by the method of galvanic substitution seems to be promising. However, the value of the standard electrode
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