Biomedical Engineering Reference
In-Depth Information
4. Take a small portion of the powder in each collector on a microscope
slide and examine under an optical microscope. Store powder from
appropriate collectors in Sterilin vials and seal the lid with parafilm to
minimise water uptake.
d
n
3
r
4
n
g
|
3
5.2.7 Expected Outcomes and Other Considerations
The powder obtained in the collectors will be a mixture of microspheres and
non-spherical particles (Figure 5.2); depending on the ratio of spherical to
non-spherical particles, the powder obtained in the collectors may be stored
for further use, discarded or recycled in the flame spheroidisation process.
The material present in the collector immediately below the flame may
contain a significant proportion of non-spherical particles; this material can
be discarded or recycled in the process to further increase the microsphere
yield. The particle size distribution of the obtained particles will reveal that
the microsphere size is independent of the glass composition, indicating
that the microsphere size range can be varied significantly by suitably
modifying the flame spheroidisation set up. The set-up described above
yields microspheres in the size range of
45 mmor
lower, particle agglomeration in the feed apparatus and subsequent dis-
persal of the agglomerates in the flame considerably limits the number of
glass microspheres obtained. This problem can possibly be overcome by
dispersing the feed particles in a suitable liquid dispersant prior to intro-
duction in the flame. At sizes of
B
10-210 mm. At sizes of
B
100 mm or higher, the residence time
of the particles in the flame is too small for achieving complete spher-
oidisation so that non-spherical particles are obtained. This problem can be
resolved by generating a flame of greater length and higher temperature to
provide a longer residence under hotter conditions. A larger blow torch
connected to a gas-oxygen source such as acetylene-oxygen may be used for
this purpose.
B
.
Figure 5.2
Scanning electron microscopy images of titanium phosphate glass
microspheres at magnifications of
100 (left) and
500 (right).
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