Page 397 - Organic Electronics in Sensors and Biotechnology

374 Chapter Ten

the resulting film is nonuniform. This has been attributed to the high
resistance of the substrates resulting from the binder added. When
o
the pellets are fired at 700 C for 0.5 h to remove the binder, the con-
ductivity of the substrate increases substantially. Consequently, the
green YSZ film obtained is of high quality.

10.2.5 Materials for EPD
The EPD technique has been used successfully for thick film of silica, 7, 38
39
nanosized zeolite membrane, hydroxyapatite (HA) coating on a metal
42
substrate for biomedical applications, 40–41 luminescent materials, high-
9
43
T superconducting films, gas diffusion electrodes and sensors, glass
c
44
18
and ceramic matrix composites, oxide nanorods, carbon nanotube
49
films, 45–48 layered ceramics, piezoelectric materials, etc. On the basis of
50
the type of material used for electrophoretic deposition, these materials
can be categorized as inorganic or organic.
Inorganic Materials
In the class of inorganic materials, EPD has been explored much for
the processing and fabrication of a wide variety of ceramic materials.
18
The EPD of ceramics was first studied by Hamaker in 1940, and only
in the 1980s did the process receive attention in the field of advanced
39
ceramics. Abdollahi et al. have applied the electrophoretic technique
as the seeding method for the formation of zeolite ZSM-5 layers in
order to achieve thin defect-free membranes with appropriate orien-
tation. Using this technique, an oriented continuous layer of nano-
sized zeolite seeds is formed on the support, and the seeds act as
nuclei for the next step, which is crystal growth under hydrothermal
51
situation. Braun et al. have reported the fabrication of transparent,
homogeneous polycrystalline alumina ceramic with submicron
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microstructure by means of EPD. Recently, Besra et al. have investi-
gated EPD of YSZ particles from their suspension in acetylacetone
onto a nonconducting NiO-YSZ substrate for solid oxide fuel cell
applications. In principle, it is not possible to carry out EPD on non-
conducting substrates. In this case, the EPD of YSZ particles on a
NiO-YSZ substrate is made possible through the use of an adequately
porous substrate. The continuous pores in the substrates, when satu-
rated with the solvent, helped in establishing a “conductive path”
between the electrode and the particles in suspension. Deposition
rate is found to increase with increasing substrate porosity up to a
certain value. EPD technique has also been explored for the nano-
crystalline oxide coatings, e.g., MnO , on the desired substrate.
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2
49
Antonelli et al. have recently reported the fabrication of dense,
crack-free, and homogeneous thick films of BCT23 (Ba Ca TiO )
0.77 0.23 3
by the electrophoretic technique. The BCT ceramic material is a fer-
roelectric material and has been reported as a promising multi-layer
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ceramic capacitor (MLCC). Trau et al. and Bohmer simultaneously
reported the monolayer film formation of micron-sized latex particles