240
7 Composites
the diffusion layer thickness of the particles and also contributed to the stability of
the suspension. The transport rate was increased so much that an eightfold enhancement in the particle incorporation rate was detected [114]. At high magnetic field,
an additional agitation-enhancing effect was identified. Since the current lines are
distorted around the partly incorporated particles and follow the surface tangent of
the particles, the external magnetic field perpendicular to the electrode also has a
Lorentz force contribution [115]. Clearly, this effect is localized to the close vicinity
of the surface of the partly incorporated particles; nevertheless, it has a same effect on
the reduction of the diffusion layer thickness as the solution stirring. The convection
effect around the particles as exerted by the perpendicular-to-cathode magnetic field
is similar to that what was found to be responsible for the modification of bubble
attachment on and removal from the cathode during either electroplating [116, 117]
or hydrogen evolution [118]. A similar analogy is true for the increase of the deposition rate in the early phase of metal electrocrystallization on a smooth substrate
under magnetic field effect [119]. The latter was named as µ-MHD effect, regarding
the size of the freshly nucleated metal particles.
7.2.6 Comparison of the Codeposition of Micrometric
and Nanometric Particles
The comparison of the codeposition of micro- and nanoparticles with metals is an
inherently uncertain field. The reason for this uncertainty is that the composition of
the particles is given with the bulk parameters. However, the synthesis of the particles
of different size often includes non-identical steps that have an immense influence
on the features of the particle surface, i.e., the part of the particle that determines
the adsorption capability and the interaction of the particles with the metal being
plated. Therefore, the “size effect” of the codeposited particles may leave intrinsic
parameters hidden that could be directly related to the codeposition behaviour. All
discussion given below should be regarded with this reservation. Nevertheless, the
investigation of the size effect in composite plating is a broad field [102–105, 107,
108, 120–126] that makes it possible to set up some trends.
A general rule for particle codeposition with metals is that the incorporating
foreign body disturbs the crystallization of the metal. This leads to a grain refinement
which is often accompanied with the loss of the deposit texture [122], simply because
the more frequent the nucleation events are, the least the preferred texture of the
freely growing deposit can manifest itself. This trend is valid for both micro- and
nanoparticles, although the effect is usually stronger for the latter.
The incorporation site of the micro- and nanoparticles may vary. While microparticles are always embedded between the crystals of the metal matrix, nanoparticles
can adopt another form of inclusion. Namely, due to their small size, they can be
embedded into a single metal crystal or accommodate themselves at the twinning
7 Composites
the diffusion layer thickness of the particles and also contributed to the stability of
the suspension. The transport rate was increased so much that an eightfold enhancement in the particle incorporation rate was detected [114]. At high magnetic field,
an additional agitation-enhancing effect was identified. Since the current lines are
distorted around the partly incorporated particles and follow the surface tangent of
the particles, the external magnetic field perpendicular to the electrode also has a
Lorentz force contribution [115]. Clearly, this effect is localized to the close vicinity
of the surface of the partly incorporated particles; nevertheless, it has a same effect on
the reduction of the diffusion layer thickness as the solution stirring. The convection
effect around the particles as exerted by the perpendicular-to-cathode magnetic field
is similar to that what was found to be responsible for the modification of bubble
attachment on and removal from the cathode during either electroplating [116, 117]
or hydrogen evolution [118]. A similar analogy is true for the increase of the deposition rate in the early phase of metal electrocrystallization on a smooth substrate
under magnetic field effect [119]. The latter was named as µ-MHD effect, regarding
the size of the freshly nucleated metal particles.
7.2.6 Comparison of the Codeposition of Micrometric
and Nanometric Particles
The comparison of the codeposition of micro- and nanoparticles with metals is an
inherently uncertain field. The reason for this uncertainty is that the composition of
the particles is given with the bulk parameters. However, the synthesis of the particles
of different size often includes non-identical steps that have an immense influence
on the features of the particle surface, i.e., the part of the particle that determines
the adsorption capability and the interaction of the particles with the metal being
plated. Therefore, the “size effect” of the codeposited particles may leave intrinsic
parameters hidden that could be directly related to the codeposition behaviour. All
discussion given below should be regarded with this reservation. Nevertheless, the
investigation of the size effect in composite plating is a broad field [102–105, 107,
108, 120–126] that makes it possible to set up some trends.
A general rule for particle codeposition with metals is that the incorporating
foreign body disturbs the crystallization of the metal. This leads to a grain refinement
which is often accompanied with the loss of the deposit texture [122], simply because
the more frequent the nucleation events are, the least the preferred texture of the
freely growing deposit can manifest itself. This trend is valid for both micro- and
nanoparticles, although the effect is usually stronger for the latter.
The incorporation site of the micro- and nanoparticles may vary. While microparticles are always embedded between the crystals of the metal matrix, nanoparticles
can adopt another form of inclusion. Namely, due to their small size, they can be
embedded into a single metal crystal or accommodate themselves at the twinning