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V. Malyshev et al.
10.1 Introduction
For the cathodic codeposition of metals, the correspondence of their crystalline
lattices and the difference in their standard electrode potentials are of great
importance. An analysis of the results of studying the electrochemical production of
alloys [1] shows that the “thermodynamic” regime of their formation is observed at
similar deposition potentials of components (≤0.2 V) and that the alloy composition
is independent of the current density over a wide concentration range. For a high
potential difference (>0.2 V), the “kinetic” regime is observed, and the alloy
composition depends weakly on the potential difference. The cathodic codeposition
of molybdenum and rhenium was studied in a chloride melt [2, 3]; they have
crystalline lattices of different types and a high difference in the standard electrode
potentials (0.45 V in a NaCl–KCl melt at 1073 K). In this case, the violation of the
growth of continuous alloy layers was ascribed to considerable diffusion difficulties
in the transport of more electropositive rhenium ions to a cathode.
The cathodic codeposition of molybdenum and tungsten in a chloride melt was
studied in [2]. They have crystalline lattices of the same type and an insignificant
difference in the standard electrode potentials (0.09 V in a NaCl–KCl melt at
1073 K). In this case, no violation was observed for the growth of continuous layers
of molybdenum–tungsten alloys. The cathodic codeposition of molybdenum and
silver, which have different types of crystalline lattices and a considerable difference
in the standard electrode potentials (0.5–0.6 V in a Na 2 WO 4 melt at 1173 K), in a
tungstate melt was studied in [4]. Since molybdenum is virtually insoluble in silver,
the latter exerts an insignificant effect on the electrodeposition of molybdenum
coatings and their properties.
It seems significant from a practical point of view to study the electrodeposition
of alloys whose components have crystalline lattices of different types but similar
electrode potentials. Molybdenum (tungsten) and nickel in a NaCl–KCl melt satisfy
these requirements. They have bcc and fcc lattices, respectively [5], and their
standard electrode potentials differ by 0.14 V in a pure halide–chloride melt based
on NaCl–KCl at 1073 K [2] and by 0.15–0.35 V (depending on the melt basicity)
in a halide–oxide melt NaCl–KCl–Na 2 MoO 4 –NiCl 2 at 1023 K [5]. As compared to
nickel, the potential of molybdenum (tungsten) in both melts is more positive, and
the compositions of the resulting continuous molybdenum (tungsten), molybdenum
(tungsten)–nickel, and nickel deposits depend on the electrolyte composition and
electrolysis conditions. A protective medium over a bath is necessary in this case.
Connected deposits are formed only on graphite, copper, nickel, and precious metal
substrates.
Oxide tungstate–molybdate melts Na 2 WO 4 –MO 3 , where M is Mo or W, were
used for the electrodeposition of molybdenum (tungsten) coatings [6, 7]. In the
present work, we study the electrochemical behavior of nickel and cobalt in a
Na 2 WO 4 melt and the possibility of electrodeposition of molybdenum (tungsten)–
nickel (cobalt) alloys from this melt. From a practical viewpoint, we are interested
in these alloys due to the use of nickel- and cobalt-based structural materials for
V. Malyshev et al.
10.1 Introduction
For the cathodic codeposition of metals, the correspondence of their crystalline
lattices and the difference in their standard electrode potentials are of great
importance. An analysis of the results of studying the electrochemical production of
alloys [1] shows that the “thermodynamic” regime of their formation is observed at
similar deposition potentials of components (≤0.2 V) and that the alloy composition
is independent of the current density over a wide concentration range. For a high
potential difference (>0.2 V), the “kinetic” regime is observed, and the alloy
composition depends weakly on the potential difference. The cathodic codeposition
of molybdenum and rhenium was studied in a chloride melt [2, 3]; they have
crystalline lattices of different types and a high difference in the standard electrode
potentials (0.45 V in a NaCl–KCl melt at 1073 K). In this case, the violation of the
growth of continuous alloy layers was ascribed to considerable diffusion difficulties
in the transport of more electropositive rhenium ions to a cathode.
The cathodic codeposition of molybdenum and tungsten in a chloride melt was
studied in [2]. They have crystalline lattices of the same type and an insignificant
difference in the standard electrode potentials (0.09 V in a NaCl–KCl melt at
1073 K). In this case, no violation was observed for the growth of continuous layers
of molybdenum–tungsten alloys. The cathodic codeposition of molybdenum and
silver, which have different types of crystalline lattices and a considerable difference
in the standard electrode potentials (0.5–0.6 V in a Na 2 WO 4 melt at 1173 K), in a
tungstate melt was studied in [4]. Since molybdenum is virtually insoluble in silver,
the latter exerts an insignificant effect on the electrodeposition of molybdenum
coatings and their properties.
It seems significant from a practical point of view to study the electrodeposition
of alloys whose components have crystalline lattices of different types but similar
electrode potentials. Molybdenum (tungsten) and nickel in a NaCl–KCl melt satisfy
these requirements. They have bcc and fcc lattices, respectively [5], and their
standard electrode potentials differ by 0.14 V in a pure halide–chloride melt based
on NaCl–KCl at 1073 K [2] and by 0.15–0.35 V (depending on the melt basicity)
in a halide–oxide melt NaCl–KCl–Na 2 MoO 4 –NiCl 2 at 1023 K [5]. As compared to
nickel, the potential of molybdenum (tungsten) in both melts is more positive, and
the compositions of the resulting continuous molybdenum (tungsten), molybdenum
(tungsten)–nickel, and nickel deposits depend on the electrolyte composition and
electrolysis conditions. A protective medium over a bath is necessary in this case.
Connected deposits are formed only on graphite, copper, nickel, and precious metal
substrates.
Oxide tungstate–molybdate melts Na 2 WO 4 –MO 3 , where M is Mo or W, were
used for the electrodeposition of molybdenum (tungsten) coatings [6, 7]. In the
present work, we study the electrochemical behavior of nickel and cobalt in a
Na 2 WO 4 melt and the possibility of electrodeposition of molybdenum (tungsten)–
nickel (cobalt) alloys from this melt. From a practical viewpoint, we are interested
in these alloys due to the use of nickel- and cobalt-based structural materials for