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Hydroxyapatite(HA) is similar in structure to the mineral
phase of bone and therefore holds a great promise as bioactive
material because it has the ability of bonding to bone. On the
other hand, as HA can be prepared in a very fine powder form and
hence it can interact actively with the surrounding atmosphere,
it is also a potential candidate for a gas sensor or catalyst
used for dehydrogenation and dehydration of primary alcohols to
aldehydes and ketones. The convenient forming method is
necessary for various applications of HA. Ceramic injection
molding is utilized in this study for mass production of HA.
This study composes of three parts : (1) the effect of
calcination on the forming and sintering of HA powder, (2) the
effect of calcination on the sintering and injection molding of
HA with paraffin wax (PW) as main binder, and (3) injection
molding and sintering of HA with water-soluble binder PEO.
The calcination treatment increases the average particle size
and changes the particle size distribution from trimodal to
monomodal for HA powder without phase transformation at high
temperatures. Higher sintering temperature is necessary for
calcining HA powder to reach a similar density level, however,
the grain size is finer in the microstructures as calcination
temperature is increased. The porosities in the sintered bodies
made from HA calcined at 1000℃ are obviously more than those
calcined at lower temperatures and 1000℃ is therefore
considered too high for calcination treatment. The
rheological behaviors of feedstock of PW-base binder and HA
indicate that lower viscosities are obtained as higher
calcination temperature is applied. The sintering properties are
believed to be a compromise of sintering driving force and
packing efficiency as calcination changes the particle size and
particle size distribution of HA. The optimum strengths of
sintered HA are 57MPa for HA calcined at 900℃ and sintered at
1350℃( for 40v/o solid content feedstock) which is thought to
be due to the finer grain size. The strength is increased as
solid content is increased to 50 v/o. The Weibull modulus of
10.62 and strength 63MPa are acquired. The better mechanical
properties are considered to be due to the finer grain size.
PEO has specific characteristics of both thermoplastic and water
soluble behaviors and is therefore chosen as a new main binder
component. The results of debinding and sintered microstructure
for samples prepared by various ratios of PEO, PEW and SA
indicate that the optimum ratio is 60:35:5 for PEO:PEW:SA. The
bonding of PEO and HA dominates the debinding defect occurrence
proposed by the mechanism of water debinding. The Weibull
modulus of HA sintered specimens with PEO pre-coating (9.77) is
higher than that without PEO pre-coating (8.46) which indicates
that PEO pre-coating increases the stability of processing HA by
injection molding.
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