Chapter 7
Composites
7.1 Composite Preparation by Codeposition of Metals
7.1.1 Principles of the Direct Codeposition of Composites
and Their Precursor Alloys
The first group of granular materials discussed is the metallic composites in which
both the matrix and the incorporated entities are formed during the deposition
process (i.e., there are no pre-existing particles that incorporate into the deposit). The
basic requirement for the electrodeposition of such a metallic composite is that the
constituents must exhibit a nearly complete immiscibility under equilibrium conditions. Since the equilibrium properties of an alloy are not necessarily indicative of
the phase(s) formed during the electroplating process, one encounters a bifurcation,
depending on whether the deposit shows the equilibrium properties of the metal pair
or a metastable alloy can form.
The first case is when the mixing enthalpy of the metals exhibits a large positive
value and their structural properties are quite dissimilar, i.e., they have either different
crystal structures or the lattice plane distances differ significantly if they are of the
same crystalline form. If these conditions prevail, the metals usually crystallize independently of each other without forming any alloy, and the deposit is the so-called
mechanical mixture. For many of the baths used for the deposition of mechanical
mixtures, the deposition potentials of the constituents can be observed in the voltammograms in the same manner as it was shown for electrodeposited multilayers (see
Fig. 5.3). Since the crystallization processes are fully unrelated to each other, the
deposition potentials of the constituents are either the same as in the absence of the
other reactant or that of the less noble metal may become more negative due to the
nucleation barrier. However, no difference can be observed in the dissolution characteristics of the phases in a mechanical mixture as compared to their elemental forms.
The codeposition mode of the mechanical mixtures is exclusively the regular one due
to the absence of any interference of the deposition processes apart from the spatial
© Springer Nature Switzerland AG 2021
L. Péter, Electrochemical Methods of Nanostructure Preparation,
Monographs in Electrochemistry, https://doi.org/10.1007/978-3-030-69117-2_7
217
Composites
7.1 Composite Preparation by Codeposition of Metals
7.1.1 Principles of the Direct Codeposition of Composites
and Their Precursor Alloys
The first group of granular materials discussed is the metallic composites in which
both the matrix and the incorporated entities are formed during the deposition
process (i.e., there are no pre-existing particles that incorporate into the deposit). The
basic requirement for the electrodeposition of such a metallic composite is that the
constituents must exhibit a nearly complete immiscibility under equilibrium conditions. Since the equilibrium properties of an alloy are not necessarily indicative of
the phase(s) formed during the electroplating process, one encounters a bifurcation,
depending on whether the deposit shows the equilibrium properties of the metal pair
or a metastable alloy can form.
The first case is when the mixing enthalpy of the metals exhibits a large positive
value and their structural properties are quite dissimilar, i.e., they have either different
crystal structures or the lattice plane distances differ significantly if they are of the
same crystalline form. If these conditions prevail, the metals usually crystallize independently of each other without forming any alloy, and the deposit is the so-called
mechanical mixture. For many of the baths used for the deposition of mechanical
mixtures, the deposition potentials of the constituents can be observed in the voltammograms in the same manner as it was shown for electrodeposited multilayers (see
Fig. 5.3). Since the crystallization processes are fully unrelated to each other, the
deposition potentials of the constituents are either the same as in the absence of the
other reactant or that of the less noble metal may become more negative due to the
nucleation barrier. However, no difference can be observed in the dissolution characteristics of the phases in a mechanical mixture as compared to their elemental forms.
The codeposition mode of the mechanical mixtures is exclusively the regular one due
to the absence of any interference of the deposition processes apart from the spatial
© Springer Nature Switzerland AG 2021
L. Péter, Electrochemical Methods of Nanostructure Preparation,
Monographs in Electrochemistry, https://doi.org/10.1007/978-3-030-69117-2_7
217