Journal of Biomaterials and Nanobiotechnology, 2011, 2, 10 3-113
doi:10.4236/jbnb.2011.22014 Published Online April 2011 (http://www.scirp.org/journal/jbnb)
Elaboration and Characterization of
Alumina-Fluorapatite Composites
Awatef Guidara, Kamel Chaari*, Jamel Bouaziz
Laboratory of Industrial Chemistry, National School of Engineering, Sfax, Tunisia.
Received November 26th, 2010; received February 20th, 2011; accepted February 28th, 2011.
ABSTRACT
Alumina and fluorapatite powder were mixed in a wet medium in order to elaborate biphasic ceramics composites. The
effect of fluorapatite addition (26.5 wt%) in the densification and the mechanical properties of the alumina matrix were
measured. The phase developments have been systematically analysed by scanning electronic microscopy, X-ray dif-
fraction, Infrared spectroscopy and 31P and 27Al magic angle scanning nuclear magnetic resonance. The Brazilian test
was used to measure the mechanical resistance of alumina-26.5 wt% fluorapatite composites. The densification and
strength rupture of composites increase versus sintering temperature and holding time. At 1600˚C, the composites den-
sities reached 85% and the rupture strength was about 22 MPa. Also, the composites sintering at 1500˚C for 5 hours
provides samples with similar density and having higher mechanical resistance, above 26 MPa. For longer holding
times, the mechanical properties were hindered by the exaggerated grain growth and the formation of intragranular
porosity. From 1400˚C, the characterization of the alumina-26.5 wt% fluorapatite composites indicates the formation of
calcium aluminates.
Keywords: Sintering, Fluorapatite, Alumina, Bioceramics, Composites, Mechanical properties
1. Introduction
Calcium phosphate-based materials have attracted con-
siderable interest in orthopedic and dental applications
because of their biocompatibility and tight bonding to
bone, resulting in the growth of healthy tissue directly
onto their surface [1-4]. Among them, fluorapatite (Fap)
has been investigated as an alternative biomedical mate-
rial [5]. This particular apatite was recognized as the
most thermally stable compound [6]. Fluorapatite has
also been considered as an attractive material for its si-
milarity in structure and composition to bone with the
added benefit of fluoride release [7]. In vitro studies have
shown that fluorapatite is biocompatible, has a better
stability [8,9] and also provides fluoride release at a con-
trolled rate to ensure the formation of a mechanically and
functionally strong bone [10]. However, the mechanical
properties of fluorapatite and all other calcium phos-
phates are generally inadequate for many load-carrying
applications [11]. These bioceramics have a low density
decreasing the mechanical properties [12-17]. Several
combinations between calcium phosphate and other
compounds have been proposed in order to improve the
poor mechanical properties of calcium phosphate [2,18-
23].
Alumina (α-Al2O3) was the first bioceramic widely
used clinically. It is used in load-bearing hip prostheses
and dental implants because of its combination of excel-
lent corrosion resistance, good biocompatibility, high
wear resistance and high strength [1].
The aim of this work was to elaborate a dense material
having adequate mechanical properties to be used essen-
tially as dental implants. Implants present the quality of
auto-protection against caries proliferation [24]. So, the
percentage of Fap is chosen to get the same bone rate of
fluoride (approximately 26.5 wt%). In bone, the fluoride
content is approximately 1 wt% (10,000 ppm) [5]. Fluo-
ride has also been administered in bone to prevent the
reduction in bone density associated with osteoporosis
even though results are still controversial [25-27]. High
fluoride levels may produce some undesired effects, one
of which is linked to an increase in bone fractures [28].
This work focuses on preparing biphasic alumina-26.5
wt% Fap composites sintered at various temperatures for
different times and to characterize the resulting compos-
ites with density and mechanical properties.

Elaboration and Characterization of Alumina-Fluorapatite Composites 104
2. Materials and Methods
The fluorapatite powder was synthesized by a wet-chem-
ical method [29-31]. Analytical grade Ca(NO3)2·4H2O,
(NH4)2HPO4 and NH4F were used as the starting materi-
als. A calcium nitrate solution is slowly poured using a
peristaltic pump into a boiling solution containing diam-
monium hydrogenophosphate; 28% NH4OH solution was
added to the mixture and the pH was adjusted to 9. The
precipitate was aged with stirring at 80˚C for 1 h, then
filtered, washed, dried at 70˚C for 12 h and calcined at
500˚C. Each undesirable synthesized powder is instantly
eliminated.
High purity α-alumina (α-Al2O3) powder (Riedel-de
haën, 98%) was used in all experiments. The Fap has
been used with 26.5 wt% amount because the human
bone contains 1 wt% of fluoride approximately [32].
The Al2O3 and Fap powder were mixed in an agate
mortar. The powder mixtures were milled in ethanol.
After milling and homogenization, the mixtures were
dried at 80˚C for 24h. After drying, the powder mixtures
were moulded in a cylinder having a diameter of 20 mm
and a thickness of 6 mm and pressed under 150 MPa.
The green compacts were sintered at various tempera-
tures and holding times. The bulk density of the sintered
body was calculated from the dimensions and weight.
Three tests were made for every experiment. The relative
error of apparent porosity value was about 1%.
The particle size dimension of the powder was meas-
ured by means of Micrometrics Sedigraph 5000. The
specific surface area (SSA) was measured by azotes ab-
sorption from the BET method (ASAP 2010) [33]. The
main particle size (DBET) was calculated by assuming the
primary particles to be spherical [30]:
6

BET
DS

(1)
where ρ is the theoretical density of Al2O3 (3.90 g/cm3)
or Fap (3.19 g/cm3), and S is the SSA of powder.
The samples before and after sintering were examined
in an X-ray diffractometer using CuKα (PHILIPS-PAN-
ALYTICAL; X’PERT pro MPD); the crystalline phases
were identified by reference to the International Center
for Diffraction Data (ICDD) cards. The samples were
also submitted to infrared (IR) spectrometric analysis
(Spectrum BX) using KBr. The Al2O3-26.5 wt% Fap
composites were characterized by high resolution solid
state using a Bruker 300WB spectrometer. NMR spectra
were recorded at a 31P frequency of 121.5 MHz (field of
7.04 T) and 27Al frequency of 78.2 MHz (field of 7.04 T).
The 31P NMR chemical shifts reference is the phosphoric
acid H3PO4. The 27Al NMR chemical shifts were refer-
enced to a static signal obtained from an aqueous alu-
minium chloride solution AlCl3·6H2O. The obtained
products were examined by scanning electron micro-
scope (SEM) (PHILIPS XL 30).
Differential thermal analysis and thermogravimetry
were carried out using about 30 mg of powder (DTA-TG;
Model Setaram). The heating and cooling rates were re-
spectively 10˚C min–1 and 20˚C·min –1. Linear shrinkage
was determined by dilatometry (Setaram) using the same
thermal cycle as the one used for DTA.
The mechanical resistance was determined by Brazil-
ian test (Lloyd EZ50). The optimum rupture strength σr
was offered by equation [17]:
2
r
F
F
SD
 
e
(2)
where F is the tensile strength and D and e are the di-
ameter and the thickness of the samples.
3. Results and Discussion
3.1. Characterization of the Ceramic Powders
The SSA, the calculated average grain sizes DBET (Equa-
tion (1)) and the particles size distribution data (meas-
ured by granulometric repartition) for Al2O3 and Fap
powder are showed in Table 1. The difference between
the value deducted by SSA (DBET) and by granulometric
repartition (D50) was probably due to the presence of
agglomerates in the initial powder.
The X-ray diffraction pattern of alumina shows only
peaks of
 phase (Figure 1(a)). The X-ray diffraction
pattern of fluorapatite powder reveals peaks of Fap and
CaO traces (Figure 1(b)). It must be kept in mind that
XRD analysis does not detect the presence of a small
amount of impurities, especially when compounds have
poor crystallinity [34]. The presence of CaO is confirmed
by the phenolphthalein test. A similar observation has
already been made [17,35]. CaO is produced by solid
reaction between CaF2 and H2O, which can be expressed
by the following equation [36]:
22
CaF + HOCaO+2HF (3)
CaF2 was contained in the synthesised Fap powder as
impurity.
IR spectra of the alumina and fluorapatite powders
(Figure 2) illustrate only alumina and fluorapatite char-
acteristic bands. From the IR spectrum of alumina (Figure
2(a)), the absorption bands at 422, 452, 500, 558, 594,
Table 1. SSA, average grain size obtained by different
analysis of Al2O3 and Fap powders.
SSA
(m2/g)
DBET (µm) ± 0.2D50 (µm) ±
0.2
da
Fap 29.00 0.07 3.00 3.19
α-Al2O3 2.87 0.53 7.00 3.90
Composites 9.80 0.40 5.94 3.70
a Theoretical density
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Elaboration and Characterization of Alumina-Fluorapatite Composites 105
Figure 1. XRD patterns for: (a) Al2O3 powder; (b) Fap
powder (*: CaO).
656 and 770 cm–1 are allotted to the group Al-O [37-40].
From the Fap one (Figure 2(b)), the absorption bands
which appear to 468, 562, 602 and 900 - 1100 cm–1 are
related to phosphate group, whereas those which appear
at 1642 and 3448 cm–1 are assigned to the adsorbed water
molecule. The absorption bands detected at 798 and 1392
cm–1 are allotted respectively to and 3
2
4
HPO NO

groups, present in the form of impurities in the initial
powder [29,41,42].
However, it is not excluded that the powders contain
other phases not detected by the IR radiations.
The 31P MAS-NMR solid spectrum of the fluorapatite
powder was presented in Figure 3(a). We observe only
one peak which appears at 2.84 ppm (only one environ-
ment of the core phosphorus), proving the absence of
secondary products accompanying the fluorapatite syn-
thesis. The 27Al MAS-NMR solid spectrum of alumina
powder was presented in Figure 3(b). We notice the pres-
ence of three peaks characteristic of aluminium; two first
ones at 7 ppm and 13 ppm corresponding to octahedral
Al sites and the other at 35 ppm which corresponds to
pentahedral Al.
3.2. Thermal Characterization of the Ceramic
Powders and the Al2O3-26.5 wt% Fap
Composites
A thermal behaviour study of the initial powders and the
composite has proved to be a powerful technique for un-
Figure 2. IR spectra of: (a) Al2O3 powder; (b) fluorapatite
powder.
derstanding physical phenomena during the sintering.
The dilatometric analysis and the differential thermal
analysis were used. Dilatometric analysis was performed
at 1500˚C. The analysis of the alumina powder shows a
light expansion followed by an even weaker contraction
(Figure 4(a)). The dilatometric measurements of alumina
powder showed that shrinkage was not begun even at
1400˚C. For the Fap powder, the shrinkage began at 950˚C
and continued to 1200˚C (Figure 4(b)). The optimum
sintering temperature of this powder is around 1030˚C.
Above 1200˚C, a slight expansion takes place, which is
probably due to the formation of a liquid phase. The ad-
dition of 26.5 wt% Fap in the matrix of alumina reduces
the shrinkage beginning temperature of about 400˚C in
comparison with pure alumina (Figure 4(c)). Therefore,
the presence of alumina delays the sintering of the Fap.
Moreover, we notice the presence of samples retractions
of about 10%, indicating the composite densification.
The alumina powder, presents an endothermic peak in
the DTA curve (Figure 5(a)), the peak around 1051˚C
probably marks the elimination of impurities potentially
present in the commercial powder (commercial Al2O3
powder contain approximately 2 wt% of impurity not
detected by XRD analysis). Typical DTA curve of Fap
powder illustrates two endothermic peaks (Figure 5(b)).
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Elaboration and Characterization of Alumina-Fluorapatite Composites 106
Figure 3. 31P NMR spectrum of fluorapatite powder and
27Al NMR spectrum of α-alumina powder.
The first is located at 180˚C, corresponding to the poder
dehydration. The second appearing at 1192˚C, probably
attributed to the formation of a liquid phase, which is
formed from binary eutectic between CaF2 and Fap
[28,29]. For the composite powder DTA, the curve pre-
sents the same transitions, but the second arises at higher
temperature (1064˚C) probably due to the presence of the
Fap (Figure 5(c)). In addition, we remark the absence of
the peak around 1192˚C attributed to the liquid phase
formation in Fap powder. This absence is probably due
to the inhibiting effect of alumina on the mixture.
After thermal analysis, we can notice that alumina was
not yet sintered at 1500˚C. The addition of Fap powder
lets the mixture sinter from a temperature about 1010˚C.
So, an optimisation of sintering conditions is required to
elaborate alumina-Fap composites.
3.3. Sintering and Characterization of the Al2O3
-26.5 wt% Fap Composites
3.3.1. Sinter i ng of the Composites
Figure 6(a) shows the mechanical properties of the
Al2O3-26.5 wt% Fap composites samples according to
the sintering temperature. The rupture strength of sintered
Figure 4. Linear shrinkage versus temperature of: (a) Al2O3;
(b) Fap; (c) Al2O3-Fap composite powders.
Figure 5. DTA curves of: (a) Al2O3; (b) Fap; (c) Fap-Al2O3
composite.
composites was slightly improved up to 1300˚C. Above
this temperature, it suddenly increases to reach its maxi-
mum value at 1600˚C (21.7 MPa). This can be attributed
to the improvement in the density of sintered composites.
So, the relative density passes from 60% at 1300˚C to
85% at 1600˚C.
The results of the mechanical properties according to
the sintering temperature are confirmed by the porosity
measurements. Indeed, the apparent porosity remains
constant until a temperature of about 1300˚C and than
decreases with the increase of sintering temperature
(Figure 6(b)). The minimum of apparent porosity reaches
14% at 1600˚C.
In order to lower the sintering temperature while
guarding the mechanical properties, other experiments
were carried out on some samples fired at 1500˚C at
various holding times (from 30 minutes to 7 hours). Fig-
ure 7(a) shows the mechanical properties evolution of
Al2O3-26.5 wt% Fap composites versus the holding time.
For 5 hours, the rupture strength reaches its maximum
value of 26.4 MPa. For longer holding times, the rupture
strength decreases abruptly. Those evolutions of me-
chanical properties can be explained by apparent porosity
results (Figure 7(b)). This curve illustrates a minimum
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Elaboration and Characterization of Alumina-Fluorapatite Composites 107
Figure 6. Mechanical resistance and total porosity versus
temperature of Al2O3-Fap composites sintered for 1h.
0
5
10
15
20
25
30
01234567
time (h)
Mech anical resista nce (MPa)
10
15
20
25
30
35
40
45
50
55
60
Total porosity (%)
(a)
(b)
Figure 7. Mechanical resistance and total porosity versus
holding time of Al2O3-Fap composites sintered at 1500℃.
apparent porosity at about 15% corresponding to the
highest rupture strength.
The whole results obtained show that it is possible to
obtain a Fap-Al2O3 composite well densified. The adopted
sintering temperatures and durations are closer to the
sintering conditions of the alumina than the fluorapatite
ones. Indeed, Fap presents a good aptitude for sintering
in the temperature range 900˚C - 1100˚C during one hour
[17,29,30,43]. Whereas the alumina sintering is carried
out in the temperatures range between 1400 and 1750℃
[44-51]. The thermal study carried out on the Al2O3-26.5
wt% Fap composite proved that mixing Al2O3 and Fap
decreases the temperature of the sintering beginning
compared to pure alumina. Indeed, it decreases from a
temperature above 1400˚C to 1030˚C. Moreover, we no-
tice that the alumina inhibits the Fap decomposition and
the liquid phase formation revealed in the sintering of
pure Fap. Further, the mechanical resistance of Fap-
Al2O3 composites showed a higher value than that of
pure Fap. F. Ben Ayed et al and N. Bouslama et al re-
ported that the mechanical resistance of Fap and TCP-
Fap ceramics was about 14 MPa and 9.4 MPa, respec-
tively [52,53].
Sintering was driven by many parameters and phe-
nomena. In fact, when powders have different grain size
and chemical nature, much driving force and phenomena
will appear. The difference of fusion temperatures and
densification start of different departure powders con-
duce to the fluctuation of the sintering process results.
All those phenomena will modify the mechanical resis-
tance and the densities of specimens [43].
3.3.2. Characterization of SinteredSamples
After sintering process, the samples have been subjected
to various characterization techniques such as the x-ray
diffraction (XRD), infrared spectroscopy (IR), 31P and
27Al magic angle spinning nuclear magnetic resonance
(MAS-NMR) and scanning electronic microscopy (SEM).
The X-ray diffraction patterns of Al2O3-Fap compos-
ites sintered at various temperatures (from 1300˚C to
1600˚C) during one hour were shown in Figure 8. The
XRD pattern of samples sintered at 1300˚C shows the
presence of Al2O3 and Fap (Figure 8a). All the diffraction
peaks correspond to the mixture of alumina and Fap.
Those spectra are identical to those of initial mixed pow-
ders. The XRD patterns of samples sintered at 1400˚C,
(a)
* °*
(b)
°
*
°
**
(c)
°
*
°*
*
(d)
20 25 3035 40 45 5055 60
2 theta (degre e s)
Figure 8. XRD spectrums of Al2O3-Fap composites sintered
at various temperatures for 1 h: (a) 1300˚C; (b) 1400˚C; (c)
1500˚C; (d) 1600˚C (*: Ca2Al2O5; CaAl12O19).
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Elaboration and Characterization of Alumina-Fluorapatite Composites 108
1500˚C and 1600˚C show in more the presence of two
new phases which are probably attributed to Ca2Al2O5
and CaAl12O19 (Figures 8(b)-(d)).
In earlier studies, many calcium aluminates phases
were produced at high temperature by decomposition of
Hap or Fap into CaO and Ca3(PO4)2 and then reacted
with alumina to form calcium aluminates [54-56]. This
decomposition is demonstrated by a relative decrease of
Fap peaks intensity [54]. For our composite, the Fap
peaks intensity is steady during the sintering process
even at high temperature. So, we can conclude that our
Fap was not decomposed and the calcium aluminates
formation is probably produced by solid reactions be-
tween CaO (as impurity) and Al2O3, which is explained
as follows [57]:
23 1219
CaO + 6AlO CaAlO (4)
232 25
2CaO + AlO CaAlO (5)
The peaks relative to the new calcium aluminates
formed have a low intensity relative to their low amount.
In addition, sintering time has not any influence on the
composition of the samples. This interpretation is illus-
trated in Figure 9.
Figure 10 and Figure 11 illustrate the FT-IR spectro-
scopic analysis; it is performed for composite samples
sintered at various temperatures and for various sintering
times. A comparison of spectra for various sintering
temperatures allows an understanding of the composite
structural evolution. Below 1400˚C, the vibrational spec-
trum is not modified. This indicates that the local struc-
ture is not modified. Indeed, most bands were character-
istic of phosphate (940-1076 cm–1) and of Al-O group of
alumina (418-752 cm–1). For higher temperature, a novel
band arises at 948cm–1 and becomes well-defined at
1600˚C [58]. This band is probably attributed to either
the Al-O stretching or bending regions of aluminium in
tetrahedral sites. This clearly indicates the formation of the
calcium aluminates, as demonstrated by X-ray analysis.
The 31P MAS-NMR spectra of Al2O3-26.5 wt% Fap
composites sintered for 1h at various temperatures
(1300˚C, 1400˚C, 1500℃ and 1600˚C) and others sin-
tered at 1500˚C for various holding times ( 1h, 2h, 3h, 4h,
5h and 6h) were presented in Figure 12(i) and Figure
12(ii) respectively. The spectra show an intense peak at
2.86 ppm and 2.88 ppm respectively related to the phos-
phorus of Fap. These results prove that the local envi-
ronment of the phosphorus atoms hasn’t changed during
the sintering process. Thus, Fap structure was conserved.
Figure 13 show the 27Al MAS-NMR spectra collected
for Al2O3-26.5 wt% Fap green composites and others
sintered for 1h at various temperatures (1300˚C, 1400˚C,
1500˚C and 1600˚C). For unsintered Al2O3-Fap compos-
ites (Figure 13(a)), the aluminium is primarily in penta-
hedral and in octahedral sites. For sintered ones (Figure 13
(a) **° *°
(b)
(c)
(d)
20 25 30 3540 45 50 55 6
0
2 theta (degrees)
Figure 9. XRD spectrums of Al2O3-Fap composites sintered
at 1500˚C for: (a) 1 h; (b) 3 h; (c) 5 h; (d) 6 h (*: Ca2Al2O5;
CaAl12O19).
(b)-(e)) the spectra consist of signals of three aluminium
environment: that for AlO4 at about 70 ppm, that for
AlO5 at about 30 ppm and 40 ppm and that for AlO6 at
about 8 ppm and 16 ppm. The intensity of tetrahedral
signal is very low compared with that of both pentahedral
and octahedral signals. The estimated concentrations of
AlO4, AlO5 and AlO6 are reported in Table 2. In heated
samples, when the sintering temperature increases, the
fraction of both the tetrahedral and pentahedral sites in-
creases at the expense of octahedral sites. In other words,
the aluminium in octahedral symmetry is forced into tet-
rahedral and pentahedral sites. According to these results,
sintering of Al2O3-Fap composites provoke the structural
rearrangement of the aluminium coordination. A similar
result was proved by G. Del Angel et al [59]. Indeed,
they show that, in presence of lanthanum, the aluminium
in octahedral symmetry is forced into tetrahedral sites.
The structural rearrangement of the aluminium coor-
dination is also probably produced by the calcium
aluminates formation which is detected by the XRD
analysis. In fact, these two products contain aluminium
in tetrahedral sites [60,61].
The SEM examination of the fracture surface of the
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Elaboration and Characterization of Alumina-Fluorapatite Composites 109
Figure 10. FTIR spectra of Al2O3-Fap composites sintered
at various temperatures for 1 h: (a) 1300˚C; (b) 1400˚C; (c)
1500˚C; (d) 1600˚C.
Al2O3-Fap composites sintered at various temperatures
(1300˚C, 1400˚C, 1500˚C and 1600˚C) for one hour was
reported in Figure 14. The fracture surface reveals a dis-
tinct difference in the samples microstructure. At 1300˚C,
the sample presents an important intergranular porosity
which disappears partially when temperature increases
(Figures 14(a)-(d)). In addition, we notice the presence of
two grain size ranges: grains which have an average size
3 µm relative to alumina phases and the others which
have an average size about 10 µm relative to Fap phases.
Above 1600˚C, the microstructure was completely trans-
formed. So, grains went through the stage of partial coa-
lescence, and then a continuous phase was developed
with the sintering temperature increase and especially at
1600˚C. A dense bioceramic was clearly formed: dense
contacts between the grains and well-formed grain bound-
ary zone.
The micrograph investigation realised for various
holding times shows that samples fired during 1 hour
until 5 hours present an improvement of structure by a
partial disappearance of porosity which reaches its
maximum during 5 hours (Figure 15(b)). For a holding
time about 6 hours, micrograph shows a reappearance of
inter and intragranular porosity which is caused by an
exaggerated grain growth and probably by impurities
Figure 11. FTIR spectra of Al2O3-Fap composites sintered
at 1500˚C for: (a) 1 h; (b) 3 h; (c) 5 h; (d) 6 h.
Figure 12. 31P NMR spectra of Al2O3-Fap composites (i)
sintered at different temperatures for 1 h; (ii) sintered at
1500˚C for different holding times.
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Elaboration and Characterization of Alumina-Fluorapatite Composites 110
Figure 13. 27Al NMR spectra of (a) unfired Al2O3-Fap
composites; (b) sintered at 1300˚C; (c) at 1400˚C; (d) at
1500˚C; (e) at 1600˚C.
volatilisation. These observations are a confirmation of
mechanical properties and porosity.
It has been shown in the present work that a fluoride
dental implant was elaborated and then characterized.
Optimum conditions of sintering were obtained. Unfor
tunately, the rupture strength of our bioceramic does not
exceed a value of about 26.4 MPa as compared to 500
10 µm
(a)
10 µm
(b)
10 µm
(c)
10
µ
m
(d)
Figure 14. SEM micrographs of Al2O3-Fap composites
sintered at various temperatures for 1 h: (a) 1300˚C; (b)
1400˚C; (c) 1500˚C; (d) 1600˚C.
Table 2. Observed proportions of AlO4, AlO5, AlO6 in Al2O3
–26.5 wt% Fap composites sintered at different tempera-
ture for 1h.
T° (℃) AlO4
AlO5 AlO6
1300 0.09 21.49 78.42
1400 0.11 21.79 78.09
1500 0.13 22.94 76.95
1600 0.30 24.42 75.29
10 µm
(a)
10 µm
(b)
10 µm
(c)
Figure 15. SEM micrographs of Al2O3-Fap composites sin-
tered at 1500℃ for: (a) 1 h; (b) 5 h; (c) 6 h.
MPa for dental enamel. However, with comparison to the
other bioceramics, such as Hydroxyapatite, fluorapatite
or tricalcium phosphate [16,17,54], our bioceramic pre-
sents higher mechanical properties with an important
porosity. And compared to alumina, properties are lower,
but the elaboration was performed at lower temperature.
As a prospect, microstructure improvement of our com-
posite can be realised by the addition of sintering agents,
like CaO, TiO2, which react at the alumina-Fap interface,
so they increase the bending forces, or by the utilisation
of physical inert reinforcement such as glass or carbon
nanofibers.
4. Conclusions
In order to imitate its higher stability and better densifi-
cation and mechanical properties, alumina was used. But
its manufacturing reclaims a very high sintering tem-
perature. Fap also presents a good sinterability, an excel-
lent biocompatibility and direct bond formation with ad-
jacent hard tissue. A marriage of both materials was de-
veloped, and a new material was successfully elaborated
for the dental replacement. Physical and mechanical
properties were studied, as well as structural characteris-
tics. The following results were obtained.
(1) Dilatometric curve of alumina indicates that the
powder was not sintered, even if we reach a temperature
about 1500˚C. However, for Fap and composite the
specimens were sintered. So Fap addition decreases the
sintering temperature of alumina.
(2) A better densification of the composite was
reached for a sintering temperature of about 1600˚C for
1 hour holding time and with rupture strength near to
22 MPa.
(3) An improvement of the rupture strength above 26
MPa, with guarding the same density, was obtained by
decreasing the temperature of 100˚C (became 1500˚C),
but for a holding time about 5 hours.
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Elaboration and Characterization of Alumina-Fluorapatite Composites 111
(4) The presence of CaO, in synthesized Fap, improves
the mechanical resistance by formation of the calcium
aluminates.
From the last notification, an improvement of densifi-
cation and mechanical properties of our composite can be
reached by adding an adequate proportion of CaO as a
sintering agent or reinforcing the structure with inert fi-
bers. This work is currently underway.
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