228
7 Composites
Therefore, electrodeposition is rendered to be a unique method for the synthesis of
such materials.
The practice of suspension plating is notorious of being an experiment-intensive
field, despite various theories have been elaborated for the incorporation ratio of the
particles and for the current density dependence of the deposit composition. The
reason for the complications stems from the fact that there is no alternative way
to measure the codeposition-related thermodynamic and kinetic parameters incorporated into the models but the evaluation of the suspension plating experiments
themselves. Thus, although the embedded physico-chemical terms can be calculated
from a series of suspension plating experiments, they cannot be used for the optimization which is hence rendered to be an experimental task. It appears that there is
a long way yet until the gap between the elementary physico-chemical parameters
of a plating system and the codeposition yield of the particles can be bridged.
7.2.2 Theories of Stability of Suspensions and Their
Coagulation
Although it is seldom emphasized in the works dealing with peculiar cases of suspension plating, the particles to be incorporated must form a stable suspension. The
hindrance of the coagulation stems from two conditions that are not independent of
each other. First, the particles have to be charged so that an electrostatic force prevents
their approach to each other. The electrostatic properties of the particle surface are
characterized with the so-called ζ-potential. Suspensions are usually stable if |ζ| >
30 mV.
The theory on the stability of suspensions and their coagulation dates back to the
mid 1900s. The name of the theory by which it is commonly known, DLVO, stems
from the initials of the authors of two important works (Derjaguin and Landau [53]
and Verwey and Overbeek [54]). On the recent progress of the DLVO theory, various
review works are available [55–57]. Below, a semi-quantitative treatment will be
offered only, and interested readers are referred to the above-mentioned works.
The basic concept of the DLVO theory is that the force between the particles
(that are taken spherical and identical in both diameter and surface charge density
in the first approximation) originates from two terms, the van der Waals force and
the electrostatic force. While the former is always attractive, the latter is repulsive.
In the DLVO theory, the total particle charge is taken as a parameter that is invariant
as the particles approach each other; nevertheless, the charge redistribution on the
surface of the particles is indeed possible, although the models usually neglect it.
Since the expressions of the two forces (van der Waals and electrostatic) depend
on different powers of the interparticle distance, their sum results in the occurrence of
various ranges of stability as a function of the distance between the particles. Instead
of the forces themselves, the total energy of the particle pairs is usually displayed as
a function of the separation distance, as it is shown in Fig. 7.2a. The minimum of
7 Composites
Therefore, electrodeposition is rendered to be a unique method for the synthesis of
such materials.
The practice of suspension plating is notorious of being an experiment-intensive
field, despite various theories have been elaborated for the incorporation ratio of the
particles and for the current density dependence of the deposit composition. The
reason for the complications stems from the fact that there is no alternative way
to measure the codeposition-related thermodynamic and kinetic parameters incorporated into the models but the evaluation of the suspension plating experiments
themselves. Thus, although the embedded physico-chemical terms can be calculated
from a series of suspension plating experiments, they cannot be used for the optimization which is hence rendered to be an experimental task. It appears that there is
a long way yet until the gap between the elementary physico-chemical parameters
of a plating system and the codeposition yield of the particles can be bridged.
7.2.2 Theories of Stability of Suspensions and Their
Coagulation
Although it is seldom emphasized in the works dealing with peculiar cases of suspension plating, the particles to be incorporated must form a stable suspension. The
hindrance of the coagulation stems from two conditions that are not independent of
each other. First, the particles have to be charged so that an electrostatic force prevents
their approach to each other. The electrostatic properties of the particle surface are
characterized with the so-called ζ-potential. Suspensions are usually stable if |ζ| >
30 mV.
The theory on the stability of suspensions and their coagulation dates back to the
mid 1900s. The name of the theory by which it is commonly known, DLVO, stems
from the initials of the authors of two important works (Derjaguin and Landau [53]
and Verwey and Overbeek [54]). On the recent progress of the DLVO theory, various
review works are available [55–57]. Below, a semi-quantitative treatment will be
offered only, and interested readers are referred to the above-mentioned works.
The basic concept of the DLVO theory is that the force between the particles
(that are taken spherical and identical in both diameter and surface charge density
in the first approximation) originates from two terms, the van der Waals force and
the electrostatic force. While the former is always attractive, the latter is repulsive.
In the DLVO theory, the total particle charge is taken as a parameter that is invariant
as the particles approach each other; nevertheless, the charge redistribution on the
surface of the particles is indeed possible, although the models usually neglect it.
Since the expressions of the two forces (van der Waals and electrostatic) depend
on different powers of the interparticle distance, their sum results in the occurrence of
various ranges of stability as a function of the distance between the particles. Instead
of the forces themselves, the total energy of the particle pairs is usually displayed as
a function of the separation distance, as it is shown in Fig. 7.2a. The minimum of