FUNCTIONALLY GRADED ALL CERAMIC HIP JOINT - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 334

10.6.2 E-Field Calculations for Electrode Design
Since the electric fi eld drives the transport and deposition of powder particles, a
uniform electric fi eld is necessary at the deposition electrode in order to obtain a
deposit that follows the contours of the electrode. A non-uniform electrical fi eld
will make electrophoretic deposition uncontrollable because a linear relation
exists between the deposition rate and the local electric fi eld strength at the elec-
trode for MEK with n-butylamine based suspensions (see Equation 10.1).
For the electric fi eld calculation, Poisson's equation in a conductive medium
is used:

2

(10.7)

λ∇ U = 0

With m) of the medium and U , the electrical potential

(V). The material properties are given in Table 10.3.
A voltage of 100V is applied between the electrodes. The resistance of the
deposit is thought to be the same as for the suspension as was shown in [Anné
et al., 2006c] for methyl ethyl keton with n - butylamine. To calculate the electric
fi eld distribution inside the EPD cell, fi nite element analysis is performed using
ANSYS 7. An element type for 2-D solids with thermal and electrical conductive
capability (PLANE67) is chosen. This element has four nodes with two degrees of
freedom, temperature and voltage, at each node.
Electric fi eld calculations are shown here for the counter-electrodes of
the acetabular cup insert. Two results in the optimization step are shown in
Figure 10.12 for spherical counter-electrodes with different diameter and position
in the cell. A perfect uniform electrical fi eld at the deposition electrode is not
possible due to the specifi c shape of the outer surface of the acetabular cup insert.
To solve this problem of non-uniform electrical fi eld, an insulating ball-shaped
PTFE cap is placed between the deposition electrode and the spherical counter-
electrode. In this (rotating) cap, small holes are made to conduct the current. The
size of the holes is determined by the local E-fi eld strength to allow uniform
deposition (Figure 10.13 ).

λ , the specifi c resistance ( Ω

10.6.3 Shaping of Homogeneous and FGM Acetabular Cup Inserts
Rigid positioning devices are needed so that the electrodes can be centered and
positioned very accurately with respect to each other in order to maintain a

TABLE 10.3. Resistance of the Materials Used in the Electric Field Calculations

Material Resistance ( Ωm) Source

Stainless steel 0.3 PolyTechnisch zakboekje, Koninklijke

PBNA nv., The Netherlands, 1998

T e fl on 1.10 20 idem

MEK 7.10 5 From our own measurements