Biomedical Engineering Reference
In-Depth Information
2. Materials and methods
In this study the main used materials are commercial tricalcium phosphate (Fluka) and
synthesized fluorapatite. The Fap powder was synthesized by the precipitation method (Ben
Ayed et al., 2000). A calcium nitrate (Ca(NO
3
).4H
2
O, Merck) solution was slowly added to a
boiling solution containing diammonium hydrogenophosphate ((NH
4
)
2
HPO
4
, Merck) and
ammonium fluorine (NH
4
F, Merck), with continuous magnetic stirring. During the reaction,
pH was adjusted to the same level (pH 8-9) by adding ammonia. The obtained precipitate
was filtered and washed with deionised water; it was then dried at 70°C for 12h.
Estimated quantities of each powder (β-TCP and Fap) were milled with absolute ethanol
and treated by ultra-sound machine for 15 min. The milled powder was dried at 120°C in a
steam room to remove the ethanol and produce a finely divided powder. Powder mixtures
were moulded in a metal mould and uniaxially pressed at 150 MPa to form cylindrical
compacts with a diameter of 20 mm and a thickness of about 6 mm. The green bodies were
sintered without any applied pressure or air at various temperatures (between 1100°C and
1450°C). The heating rate was 10°C min
-1
. The green compacts were sintered in a vertical
resistance furnace (Pyrox 2408). The relative densities of the sintered bodies were calculated
by the dimensions and weight. The relative error of densification value was about 1%.
The received powder was analyzed by using X-ray diffraction (XRD). The X-rays have used
the Seifert XRD 3000 TT diffractometer. The X radiance was produced by using CuK
α
radiation (λ = 1.54056 Å). The crystalline phases were identified from powder diffraction
files (PDF) of the International Center for Diffraction Data (ICDD).
The samples were also submitted to infrared spectrometric analysis (Perkin-Elmer 783)
using KBr.
Linear shrinkage was determined by dilatometry (Setaram TMA 92 dilatometer). The
heating and cooling rates were 10°C min
-1
and 20°C min
-1
, respectively.
Differential thermal analysis (DTA) was carried out using about 30 mg of powder (DTA-TG,
Setaram Model). The heating rate was 10°C min
-1
.
The
31
P magic angle spinning nuclear magnetic resonance (
31
P MAS NMR) spectra were run
on a Brucker 300WB spectrometer. The
31
P observational frequency was 121.49 MHz with 3.0
µs pulse duration, spin speed 8000 Hz and delay 5 s with 2048 scans.
31
P shift is given in
parts per million (ppm) referenced to 85 wt% H
3
PO
4
.
The microstructure of the sintered compacts was investigated by scanning electron
microscope (Philips XL 30) on fractured sample surfaces. Because calcium phosphates are
insulating biomaterial, the sample was coated with gold for more electronic conduction.
The particle size dimension of the powder was measured by means of Micromeritics
Sedigraph 5000. The specific surface area (SSA) was measured by the BET method using
azotes (N
2
) as an adsorption gas (ASAP 2010) (Brunauer et al., 1938). The main particle size
(D
BET
) was calculated by assuming that the primary particles are spherical (Ben Ayed et al.,
2001b):
6
D
(1)
BET
s
Where ρ is the theoretical density of β-TCP (3.07 g.cm
-3
) or Fap (3.19 g.cm
-3
) and s is the SSA.
The Brazilian test was officially considered by the International Society for Rock Mechanics
(ISRM) as a method for determining the tensile strength of rock materials (ISRM, 1978). The
Brazilian test was also standardised by the American Society for testing materials (ASTM) to
