SYNTHESIS OF CALCIUM-PHOSPHATE MICROSPHERE WITH WELL-CONTROLLED PARTICLE SIZE BY ULTRASONIC SPRAY-PYROLYSIS TECHNIQUE AND THEIR SINTERABILITY MAMORU AIZAWA 1,ATSUSHI ONO 1,TOSHIKI OHNO1, and PAK-KON CHOI2 1) Department of Industrial Chemistry, 2) Department of Physics ,School of Science and Technology, Meiji University, 1-1-1 Higashimita, Tama-ku, Kawasaki, 214-8571, Japan, e-mail:
[email protected] Abstract: We performed to synthesize the calcium-phosphate well-controlled particle size by changing the frequency transducer. The crystalline phases of the resulting powders β-tricalcium
phosphate
were
1.50.
about
The
were
composed
of
sizes
increased
with
quite
narrow.
The
controlled
by
(ƒÀ-TCP) SEM
and
observation
microspheres
with
decreasing above
changing
hydroxyapatite indicated a diameter
ultrasonic results the
(HAp);
show frequency
that
of •`1
frequency that of
the the
to •`2.5 , and
the
microsphere with of the ultrasonic were composed of
particle
ultrasonic
the
Ca/P
mola r ratios powders
resulting gm
.
The
particle
distributions size
can
transducer
were be
easily during
spray-pyrolysis.
INTRODUCTION Hydroxyapatite (Ca10(PO4)6(OH)2; HAp) and tricalcium phosphate (Ca3(PO4)2; TCP) are widely used as biomaterials for substituting with human-hard tissues1. We have synthesized the above-mentioned HAp and the apatite-family compounds by ultrasonic spray-pyrolysis technique and examined the properties the resulting powders2-5). An ultrasonic spray-pyrolysis technique is one of the powder preparation techniques via the liquid phases. This technique has advantagesthat one canprepare the stoichiometric and homogeneous compounds instantaneously by spraying the solutions with the desired amounts of cations into the hot zone of electronic furnace. In the case of the powder preparation based on ultrasonic spray-pyrolysis , the particle size is dependent on the size of droplet generated by ultrasonic transducer . The droplet size, dp, is defined by the following equation 5).
1
where, f the
is a frequency, ƒÏ
particle
of
sizes
droplet
by In
the
resulting
changing the
bioceramics, using
of
present
of
solution
solution, ƒÐ
have
calcium-phosphate
the
Ca/P
ratio
transducer,
if one
on
of
to
one
powders 1.50.
Our
well-controlled
and
tension. can
Thus,
control
the
size
transducer. focused
the
with
a surface
well-controlled
ultrasonic
we
with
ultrasonic
be
in the
microspheres
the
spraying
may
frequency
prepared
calcium-phosphate
frequency
the
investigation,
and
starting
of
powder
the
TCP,
the
density
of
the
biodegradable
via
the
above
were
to
aims
particle
examine
the
size
by
sinterability
process synthesize
changing
of
the
the
resulting
powders.
EXPERIMENTAL
Calcium-phosphate
powders
solution.
The
starting
Ca(NO3)2,
0.40
mol•Edm-3
formed
by
2.5
3 MHz.
and
As
of
set
at
two
resulting
diffractometry
(XRF),
measurement
of
0.2
sintered g•Ecm-3).
phase
was
RESULTS of
frequency fraction
as-prepared
the
by
solution
mixing
zone
present
0.60 The
at the
hot
the
the
of
present
investigation,
higher
one
at
the
850•Ž
molidm-3
droplets
frequency
of
for
starting
were
0.5,
1, 1.5,
apparatus
was
lower
furnace
pyrolysis
of
the
The
relative by
The
at
the
the
AND
DISCUSSION
ultrasonic
from that
0.5 the
examined based of ƒÀ-TCP
to
3.0
as-prepared sample on
typical phase
microscopy
(SEM),
1050,
1150 was
theoretical
was
techniques:
X-ray
(FT-IR), and
of
uniaxially
10
and
mm
BET
X-ray
method
densities
pressed
and
1200•Ž
calculated
was
above
the
following
spectrophotometry
diameter
for
for
by
using
100
thickness
5
h
dividing
of ƒÀ-TCP
observed
a
at
heating bulk
SEM
rate:
density
(3.07g•Ecm-3) a
to
of•`2mm.
(the the
MPa
of
and ƒ¿-TCP
and
the
crystalline
XRD.
,
frequenc
1 shows
the
infrared
a
microstructure by
by
powder
density
identified
the
characterized
area.
with
fired
Figure
the
g of
compact
(3.07
all
mol•Edm-3NHO3.
and
electron surface
were
10•Ž.min-1).
indicated
0.40
the
transform
specific
compact
compacts
were
scanning
disk-shaped
frequency
In
droplets
Fourier
the
About
Effect
of
powders
(XRD),
fluorometry
the
drying
prepared
2-5), the
furnaces.
spray-pyrolysing
was
starting
reported
by
salts. The
The
and the
previously
for
synthesized
solution
(NH4)2HPO4
electric
300•Ž
precipitated
form
aqueous
ultrasonically-vibrating
composed was
were
on
XRD MHz
the powder properties
patterns on
XRD decreased
the
powders
spray-pyrolysis
powders powders.
of
were As
process.
composed
examining
intensities
the
2
down
by
These
of ƒÀ-TCP
of ƒÀ-TCP
from•`65%
prepared
phase
and changes
(0210) to•`45%
and
changing XRD
HAp with
the patterns
biphase
in
ultrasonic
HAp
(211),
with
increasing
the
Figure ultrasonic
frequency, In
assigned
the
to
absorption
of
absorption
PO4
phase
of
0.03.
group
is,
of
above
the
resulting
The
Ca/P
Ca/P=1.50.
Figure
group
were
group
cm-1
the
the
results
increased
above
assigned
in
that
the
.
powders 600 3570
, the
and cm-1
570 .
cm-1
In
NO3-groupderived , except
NO3-
absorptions , and
the
addition,
the
from
starting
are
assigned
group,
ultrasonic
of
frequency
influences
the
crystalline
powders. the
harmony the
the
absorptions
calcium-phosphate
are
to
at
to•`55%
HAp.
show
ratios
up
1300-900,
detected
These
and
from•`35%
at
slightly was
powders.
calcium-phosphate
detected
HNO3. TCP
of the as-prepared
HAp
was
Thus,
calcium-deficient
of of
molar
values
patterns
spectra
and
The
These
that
1600-1300
Ca(NO3)2
to the
that
PO4 OH
of
materials,
while
FT-IR
the
1 XRD
apatite
resulting
with
the phase
powders
were
stoichiometric present
in
the
composition in
the
resulting
range of
of
1 .50 •}
TCP
powder
phase may
, be
apatite. 2
shows
the
particle
morphologies
of
the
resulting
powders
Figure 2 SEM micrographs of the resulting calcium-phosphate powders: (a) Ultrasonic frequency: 0.5 MHz, (b) 1.5 MHz, (c) 3.0 MHz.
3
((a)
ultrasonic that
frequency:
the
∼2 .5
as-prepared
ƒÊm
the
measuring
to
the
of
the
diameters in
(c)
3 MHz)
composed
increased
than
of
of
the
.
of
with
These
SEM
microspheres
micrographs with
decreasing
of
solvent
from
In
the
mean
particle
frequency
from
above
observations
resulting
indicated
a diameter
ultrasonic
with
.
The .
the
frequencv
results
of be
the
increased
of the
due
from
1
in
of•`1
to
. and
the
size
by
particle
each
droplet
sample)
generated
the
.0 to
spray
2.5 ƒÊm
The
particle
shrinkage
during
. according
spray-pyrolysized to
droplet
mean
-376
diameter
may of
determined (n=253
diameter
surface
3 down
the
This
size
, we
particles
together
droplet
evaporation
The
the
frequencies
that
addition,
SEM
Fig . 3,
ultrasonic
ultrasonic
and
were
sizes
bases
illustrated
various
smaller
particle
1.5,
were quite narrow.
On
is
(b)
powders
The
distributions
result
0.5,
was
based
-pyrolysis
with
on
the
process
a decrease
of
. the
to 0 .5 MHz.
indicate
that
the
particle
size
can
be
easily
controlled
b y
changing
the
frequency
Figure
of
transducer
during
3 Relationship
between
mean
frequency,
together
with
ultrasonic The
ultrasonic
sinterability
of
the
spray
particle
-pyrolysis
.
size and
the size of the droplet
calcium-phosphate
microspheres
.
was
ex
Figure
4
amined ring
the
green
relationship
compacts
between
at
firing
800
,
1050
and
temperature
and
1200 •Ž relative
for
5
density
h. of
shows
the sintered
In
the
case
of
the
firing
temperature
all
the
examined
specimens.
compact.
This
This
at
800 •Ž
value
was
almost
the
that
the
firing
, the
relative
density same
as
was the
compact.
about
relative
50%
insufficient
to promote
result the
sintering
suggests of
the
resulting
4
powders
temperature .
of
in
d ensity
green
by fi the
800 •Ž
of is
Figure 4 Relationship the sintered compact On the
case
of
the the
in
slightly
decreased be
all
the
due
hands,
firing
density
may
other
transformation
relative
temperature
examined and
to
the
the
between relative density and ultrasonic frequency.
at
densities
1050•Ž
specimens.
the
values
In
were
in
the
were
and
these
the
case
ranges
in
the
values of
of
range were
1200•Ž
of
84%
of the
highest
, the to
92%
90%
to
96% relative
relative .
This
density decrease
phase
of ƒÀ-TCP
into ƒ¿-TCP. Actually, crystalline
phase
sintered and
compact
1050•Ž
phase that
was
the
the
at
800
a single
was of ƒ¿-TCP.
FT-IR
spectra
sintered
while
compact
phase
a
at single The
of
the
compacts
indicated
also
that
absorptions the
of
of ƒÀ-TCP, of
1200•Ž
to
the
were PO4
group
the assigned of
the Figure
5 Microstructure
5
of
typical ƒÀ-TCP
ceramics.
in
TCP
phase.
The
NO3-
group
present
in
the
as-prepared
powder
disappeared
after
firing. Among relative
density
frequency: Fig.
5.
be
MHz,
It was of
during
obtained
the
grain
by
conclusion,
the we
particle
the
sizes
make can
that
be
The
that
of
2-3
easily
the
.ƒÊm.
with
of
ultrasonic
microstructure
Thus,
96%
powder; is
dense ƒÀ-TCP
at 0.5
the
ceramics
sample
5 h.
frequency
clear
dense
following
observation
ultrasonic
sizes
spray-ovrolysis
the
most
1050 •Ž,
SEM
with
setting
the
from
conditions:
from
uniform
well-controlled
specimens,
firing
seen
obtained In
examined
were
0.5
composed may
the
shown
ceramics
easily-sinterable
in were
powder
MHz
calcium-phosphate
synthesized
by
microspheres changing
with
the
frequency
technique.
CONCLUSION
We
performed
well-controlled The
particle
crystalline
The
Ca/P
the
the
The
maximum of
ultrasonic
by
were
about
with
in
were
show
that
of
the
of
the
SEM
powder
the
with
particle
of•`1 the
can
be
and
that
easily
were
controlled In
the
the
to•`2.5 ƒÊm.
distributions
spray-pyrolysis.
by
biphase.
indicated
and
sinterability prepared
transducer.
of ƒÀ-TCP/HAp
a diameter
size
with
ultrasonic
observation
during
a good
microsphere
composed
frequency,
transducer had
case
The
ultrasonic
ultrasonic
the
frequency
microspheres
the
microsphere 96%
the powders
of
results
calcium-phosphate
1.50.
composed
of
the
changing
resulting
above
frequency
synthesize
the
increased
calcium-phosphate
attained MHz
were
sizes
narrow.
changing
of
ratios
powders
particle
quite
size
phases molar
resulting The
to
relative
spray-pyrolysing
by
addition, density at 0.5
frequency.
ACKNOWLEDGMENT
A part of the present research is supported by the Research Project (A) by Institute of Science and Technology Meiji University. REFERENCES 1) L. L. Hench, J. Am Ceram. Soc., 81, 1705-28 (1998). 2) M. Aizawa, F. S. Howell and K. Itatani, J.Ceram. Soc.Jpn., 107, 1007-1011 (1999). 3) M. Aizawa, T. Hanazawa, K. Itatani, F. S. Howell and A. Kishioka, J. Mater. Sci., 34, 2865-2873 (1999). 4) M. Aizawa, T. Hanazawa, K. Itatani, F. S. Howell and A. Kishioka, Phosphorus Res., Bull., 6, 217-220 (1996). 5) K. Itatani and M. Aizawa, J. Soc. Inorg. Mater. Jpn., 10, 285-292(2003).
6