234
7 Composites
7.2.4 Experimental Observation of the Metal Growth During
Particle Codeposition
The in situ detection of the evolution of the shape of the metal growing around a
particle being incorporated is by far not a straightforward task. A very smart way
of indirect detection of the growing fronts of the metal matrix was developed by
Stappers and Fransaer [69]. Although their study was performed with particles of
a diameter of several micrometre, it revealed many important aspects of the field.
The method of the study was that the particles were sedimented on the bottom
of the electrochemical cell that served as the cathode. The metal deposited was a
Fe–Ni alloy whose composition was modulated by applying two current pulses of
different current densities. Hence, the composition contours in the SEM image of
the cross-sectionally cut deposits revealed the temporal evolution of the process.
The observation of the incorporation of glass particles revealed that the particle
immobilization started much after the start of the deposition, although the particle
touched the cathode at the beginning of the process. The interaction between the glass
particle and the metal was relatively weak as compared to that occurring in typical
suspension plating systems. For this reason, the glass particle was raised physically
by the deposit growing underneath. The cross-sectional image also showed that the
particle was not totally fixed when the metal grew already around the particle but
the upward motion of the particle could continue during the incorporation process.
This is why a cavity formed under the particle. The curvature of the metal layers of
dissimilar composition in the close vicinity of the bottom side of the glass particle
indicated a preferential metal growth near the triple phase junction even in the phase
when the particle was not yet fixed.
A pronounced difference was observed in the incorporation manner, depending on
the nature of the particles used. In the first case, the particle being incorporated was
non-conducting and hydrophobic, which also means that the surface concentration of
the adsorbed metal ions is probably small. The cross-sectional figure showed that the
growth profile was uniform from the start of the incorporation until the half-covered
state of the particle since the composition contour lines were parallel to the substrate.
However, the overgrowth of the metal can be seen after the deposit reached the half
of the particle, and the top part could be covered only when the metal layer far
from the particle was much thicker than the particle diameter. This means that, even
though the particle was hydrophobic, the particle–metal interaction was even weaker
than the particle–solution interaction. In the second case, the metal growth around
a graphite particle was studied. Although the nucleation of metals is much hindered
on carbonaceous materials, the coverage of the graphite particle with the growing
metal preceded the rate of the metal deposition far from the particle significantly. As
the contour lines showed, the graphite particle was covered with the growing metal
nearly instantaneously.
The relative thickness of the same metal layer on various spots near the particle
accounts for the current density distribution. It was a common experience that,
regardless of the material of the particle being incorporated, the metal deposition
7 Composites
7.2.4 Experimental Observation of the Metal Growth During
Particle Codeposition
The in situ detection of the evolution of the shape of the metal growing around a
particle being incorporated is by far not a straightforward task. A very smart way
of indirect detection of the growing fronts of the metal matrix was developed by
Stappers and Fransaer [69]. Although their study was performed with particles of
a diameter of several micrometre, it revealed many important aspects of the field.
The method of the study was that the particles were sedimented on the bottom
of the electrochemical cell that served as the cathode. The metal deposited was a
Fe–Ni alloy whose composition was modulated by applying two current pulses of
different current densities. Hence, the composition contours in the SEM image of
the cross-sectionally cut deposits revealed the temporal evolution of the process.
The observation of the incorporation of glass particles revealed that the particle
immobilization started much after the start of the deposition, although the particle
touched the cathode at the beginning of the process. The interaction between the glass
particle and the metal was relatively weak as compared to that occurring in typical
suspension plating systems. For this reason, the glass particle was raised physically
by the deposit growing underneath. The cross-sectional image also showed that the
particle was not totally fixed when the metal grew already around the particle but
the upward motion of the particle could continue during the incorporation process.
This is why a cavity formed under the particle. The curvature of the metal layers of
dissimilar composition in the close vicinity of the bottom side of the glass particle
indicated a preferential metal growth near the triple phase junction even in the phase
when the particle was not yet fixed.
A pronounced difference was observed in the incorporation manner, depending on
the nature of the particles used. In the first case, the particle being incorporated was
non-conducting and hydrophobic, which also means that the surface concentration of
the adsorbed metal ions is probably small. The cross-sectional figure showed that the
growth profile was uniform from the start of the incorporation until the half-covered
state of the particle since the composition contour lines were parallel to the substrate.
However, the overgrowth of the metal can be seen after the deposit reached the half
of the particle, and the top part could be covered only when the metal layer far
from the particle was much thicker than the particle diameter. This means that, even
though the particle was hydrophobic, the particle–metal interaction was even weaker
than the particle–solution interaction. In the second case, the metal growth around
a graphite particle was studied. Although the nucleation of metals is much hindered
on carbonaceous materials, the coverage of the graphite particle with the growing
metal preceded the rate of the metal deposition far from the particle significantly. As
the contour lines showed, the graphite particle was covered with the growing metal
nearly instantaneously.
The relative thickness of the same metal layer on various spots near the particle
accounts for the current density distribution. It was a common experience that,
regardless of the material of the particle being incorporated, the metal deposition