Biomedical Engineering Reference
In-Depth Information
If the powder
i
is a mixture of different components
X
j
, the wt% of compo-
nent
X
j
in the deposited layer
Δ
d
is given by:
t
1
dy
dt
∑
∫
i
Xwt
(
%
) =
X
dt
(10.4)
j
ij
,
i
Δ
Y
tot
i
t
1
with
X
i
,
j
wt% of component
j
in powder
i
.
The thickness increase of the deposited layer
Δ
d
during
Δ
t
is given by:
Δ
Y
tot
ρ
Δ
d
=
(10.5)
the green density as a function of the local composition if the compo-
sition as a function of green thickness is desired or with
With
ρ
the theoretical density
for the local composition if the composition as a function of sintered thickness is
wanted.
At time
t
, the thickness
d
of the disc is:
ρ
t
()=
∫
Δ
0
dt
ddt
(10.6)
By means of equations 10.1 through 10.6, the concentration profi le in an
FGM disc can be predicted provided that the factor
f
i
i
is determined for the
individual powder particles by experiments on the pure powder
i
[Ann é , 2005b ].
This is proven in the next paragraph for symmetrical Al
2
O
3
/Y - ZrO
2
FGM discs.
μ
10.5.3 Controlled Processing of FGM Discs
The starting materials are 3 mol% Y
2
O
3
co - precipitated ZrO
2
powder (Daiichi
HSY - 3U, 3 mol% Y
2
O
3
co - precipitated) and
- Al
2
O
3
powder (Baikowski grade
SM8). A MEK (Acros, 99%) with 10 vol.% n-butylamine (99.5%, Acros) and 1
wt% nitrocellulose (Aldrich, 435058-250 g) solution is used as suspension medium.
The set-up for the graded plates, schematically presented in Figure 10.4, is
composed of a suspension fl ow-through deposition cell, a suspension circulation
system driven by pump one, a mixing cell where two suspensions are mixed by a
magnetic stirrer, and a suspension supply system to add a second suspension to
the circulating suspension in the mixing cell at a controlled rate. The distance
between the fl at disc shaped electrodes (
α
= 43 mm) is 35 mm.
For the deposition of a semi-symmetrical disc, a 175 ml starting suspension I
containing 70 g/l Al
2
O
3
is pumped through the deposition cell by peristaltic pump
one at a rate of 2.5 ml/s. After 100
s
of deposition, 125 ml of suspension II with
135 g/l of an Al
2
O
3
/ZrO
2
(70 vol. % Al
2
O
3
) mixture is added to the circulating
suspension by pump two. After 570
s
, the addition of suspension II is completed.
During the subsequent step, the suspension is circulated for 630 sec without any
further additions. Afterwards, 140 ml of suspension III with 150 g/l Al
2
O
3
is added
φ
Search WWH ::
Custom Search