7.2 Composite Deposition from Particle Suspensions
245
in the deposit surface roughness was a significant factor of the enhancement of the
water contact angle beside the hydrophobic properties of the particles themselves.
For further superhydrophobic deposits, see also Chap. 8.2.
7.2.10 Suspension Plating with Magnetic Particles
In this chapter, we deal with composite deposits in which the particles incorporated into the coating are magnetic and the motivation of the experiments does
stem from the magnetic properties of the system. The process is often named as
magnetic composite electroplating (MCE). The application of an external magnetic
field applied during the deposition often plays an important role in the magnetization
behaviour of the resulting systems. Since the suspended magnetic particles interact
with each other, both the application of a sufficient surfactant and the agitation of the
bath are of high importance to solubilize the particles and to prevent their accumulation. The uniform particle dispersion is often achieved with a long stirring and/or
ultrasonic agitation prior to the electrodeposition.
The incorporation of magnetic particles into a non-magnetic matrix can give
rise to the occurrence of permanent magnetic properties in the case when the metal
matrix itself if not ferromagnetic. For suspension plating of Ni particles with a Zn
matrix on a magnetic steel substrate, it was found [172] that the matrix–particle
magnetic interaction is predominant while the particle–particle interaction is not. As
a consequence, the local concentration of the Ni particles in the coating was larger
in the near-substrate zone by a factor of 4 than in the bulk deposit. In accord with
the importance of the substrate–particle magnetic interaction, the incorporation ratio
increased with the remanence magnetization of the Ni particles. For the codeposition
of magnetite with Cu metal as matrix [173], the particle distribution was found to
be even along the depth of the coating, although an external magnetic field was
necessary to achieve significant particle incorporation. For the deposition of the
Cu(Fe 3 O 4 ) system, a relatively low temperature and a moderate stirring rate was
necessary. The deposition was successful in the mass transport-limited regime of Cu
deposition, which means that the negative surface charge of the substrate may have
a role in the magnetite particle adhesion to the Cu matrix.
If the metal matrix itself is ferromagnetic, its material is also important for the
resulting magnetic properties of the composite. While Ni is a popular material as a
carrier of the magnetic particles due to the simplicity of its deposition [174–176],
Ni alloys with either Co [177–181] or Fe [182] can improve the magnetic properties. For optimization, matrices as complex as Co–Ni–P [183–185] or Co–Ni–Mn–P
also often occur [174, 186, 187], which can be rationalized by the magnetic properties of the substrate. What concerns the codeposited magnetic particles, barium
ferrite (BaFe 12 O 19 ) [174, 177, 178, 180, 181, 183–187] or barium-strontium ferrite
(Ba 0.2 Sr 0.8 Fe 12 O 19 ) [179] are the most common since they exhibit both high magnetization and high coercivity (3.2–3.8 kOe). In such cases, the coercivity of the deposit
is meant to be larger than the matrix alone, while the saturation magnetization usually
245
in the deposit surface roughness was a significant factor of the enhancement of the
water contact angle beside the hydrophobic properties of the particles themselves.
For further superhydrophobic deposits, see also Chap. 8.2.
7.2.10 Suspension Plating with Magnetic Particles
In this chapter, we deal with composite deposits in which the particles incorporated into the coating are magnetic and the motivation of the experiments does
stem from the magnetic properties of the system. The process is often named as
magnetic composite electroplating (MCE). The application of an external magnetic
field applied during the deposition often plays an important role in the magnetization
behaviour of the resulting systems. Since the suspended magnetic particles interact
with each other, both the application of a sufficient surfactant and the agitation of the
bath are of high importance to solubilize the particles and to prevent their accumulation. The uniform particle dispersion is often achieved with a long stirring and/or
ultrasonic agitation prior to the electrodeposition.
The incorporation of magnetic particles into a non-magnetic matrix can give
rise to the occurrence of permanent magnetic properties in the case when the metal
matrix itself if not ferromagnetic. For suspension plating of Ni particles with a Zn
matrix on a magnetic steel substrate, it was found [172] that the matrix–particle
magnetic interaction is predominant while the particle–particle interaction is not. As
a consequence, the local concentration of the Ni particles in the coating was larger
in the near-substrate zone by a factor of 4 than in the bulk deposit. In accord with
the importance of the substrate–particle magnetic interaction, the incorporation ratio
increased with the remanence magnetization of the Ni particles. For the codeposition
of magnetite with Cu metal as matrix [173], the particle distribution was found to
be even along the depth of the coating, although an external magnetic field was
necessary to achieve significant particle incorporation. For the deposition of the
Cu(Fe 3 O 4 ) system, a relatively low temperature and a moderate stirring rate was
necessary. The deposition was successful in the mass transport-limited regime of Cu
deposition, which means that the negative surface charge of the substrate may have
a role in the magnetite particle adhesion to the Cu matrix.
If the metal matrix itself is ferromagnetic, its material is also important for the
resulting magnetic properties of the composite. While Ni is a popular material as a
carrier of the magnetic particles due to the simplicity of its deposition [174–176],
Ni alloys with either Co [177–181] or Fe [182] can improve the magnetic properties. For optimization, matrices as complex as Co–Ni–P [183–185] or Co–Ni–Mn–P
also often occur [174, 186, 187], which can be rationalized by the magnetic properties of the substrate. What concerns the codeposited magnetic particles, barium
ferrite (BaFe 12 O 19 ) [174, 177, 178, 180, 181, 183–187] or barium-strontium ferrite
(Ba 0.2 Sr 0.8 Fe 12 O 19 ) [179] are the most common since they exhibit both high magnetization and high coercivity (3.2–3.8 kOe). In such cases, the coercivity of the deposit
is meant to be larger than the matrix alone, while the saturation magnetization usually