Int. J. Appl. Ceram. Technol., 11 [1] 31–46 (2014)
DOI:10.1111/ijac.12047
A New and Economic Approach to Synthesize and
Fabricate Bioactive Diopside Ceramics Using a Modified
Domestic Microwave Oven. Part 1: Study of Sintering
and Bioactivity
Abdelhamid Harabi* and Souheila Zouai
Physics Department, Ceramics Laboratory, Mentouri University- Constantine,
Constantine 25000, Algeria
Diopside (CaMgSi2O6) ceramics was synthesized and fabricated by a simple solid-state reaction rather than other used
processes. This new and economic approach for diopside fabrication consists mainly of replacing the usually used starting
materials by other more economic (activated CaOMgO powders), using conventional sintering and microwave sintering. The
P2O5 addition (0.5–5.0 wt%) promotes sintering, crystallization, and bioactivity. Additionally, a considerably low weight loss
ratio (0.21%) was also obtained for these samples, after 2 days of soaking in lactic acid. Carbonated hydroxyapatite (CHA)
formation in simulated body fluid was confirmed for all sintered samples. Both sintering and CHA formation mechanisms
were proposed.
Introduction
Since the discovery of biologically active glass, Bioglassâ, by Hench et al. in 1970,1 much research has
been carried out to apply glasses and glass–ceramics as
human tissue substitutes. Actually, various kinds of bio*[email protected]
© 2013 The American Ceramic Society
active glasses and glass–ceramics have been developed
for use as biomedical materials.2–4 Because of its close
physical and chemical properties to mineral part of bone
and teeth, hydroxyapatite (HA: Ca10(PO4)6(OH)2) is
one of the most attractive materials for human hard tissue implants.5–7 Even though the biocompatibility of
this ceramic is good enough, when used as an implant
material, it forms a direct bonding with the neighboring
bone. By contrast, their poor mechanical properties are
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International Journal of Applied Ceramic Technology—Harabi and Zouai
one of the most serious obstacles for wider applications.8 Therefore, to avoid all these drawbacks, selecting
another material called diopside (CaMgSi2O6) is of
great importance. This alternative material may be significantly considered as a low-price bioceramics because
of the abundance of the dolomite (CaCO3MgCO3),
which is used in this work as a starting material, similarly to what has been reported in reference.9,10
Calcium silicate–based biomaterials including
bioglass are nowadays a hot topic of research for bone
tissue repair applications.11 Diopside belongs to the
group of silicate biomaterials, and they have the ability
to release silicate ions at a given concentration, which
helps osteoblasts to grow and differentiate.12 It has
been reported that the diopside has the ability to
induce apatite formation in vitro in simulated body
fluid (SBF) and bone formation in vivo.13 Furthermore,
it has been confirmed that the diopside possesses good
bioactivity and excellent bending strength, fracture
toughness both in vitro and in vivo.14 Based on these
considerations, diopside could therefore be considered
to be potential biomaterial for artificial bone and tooth.
Nonami and Tsutsumani14 found that diopside
has a fairly high mechanical strength and a satisfactory
biological affinity. According to a series of reports on
diopside, the sintered body of diopside forms an apatite
layer on the surface in contact with SBF,15,16 and
bonding reacts with living bone tissues more rapidly
than HA in animal experiments.14
Generally, diopside powders are synthesized by
solid-state reaction in conventional furnace. This conventional synthesis is the simplest method for the
industrial manufacturing.17 However, this method
requires high temperatures (over 1300°C) and long
reaction time.18 Thus, the use of new and highly efficient heating technique for solid-state synthesis is of
interest. Microwave has been extensively utilized for
heating materials due to the fact that microwave processing promotes many interesting advantages over the
conventional process.
Microwave is an electromagnetic wave, which can
couple dielectric materials and consequently generate
volumetric heating. A unique characteristic of microwave processing is rapid heating because materials are
heated directly through the interaction with microwave
energy, which is opposite to the slow heating by convection heating in a conventional furnace. The higher heating rate brings about the reduction in energy
consumption as well as manufacturing time and cost.
Vol. 11, No. 1, 2014
Moreover, the volumetric heating yields a uniformity of
product. By microwave processing, materials are heated
differently depending on their dielectric property. This
condition allows selective heating and possibly achievement of new materials. Many of research studies have
demonstrated the viability of microwave applications on
ceramic materials such as synthesizing, calcination, and
sintering.19–22 Most of the ceramic materials cannot
absorb microwave because they have a low dielectric loss
factor. However, the dielectric loss factor can increase
with temperature; then the materials can absorb microwave more efficiently. Application of a microwave susceptor as the secondary heat source is one of the most
effective ways to accelerate the heating process. SiC has
been widely used as a susceptor for microwave heating
of ceramic materials because of its excellent loss factor.
The technique in which microwave energy is applied to
a sample accompanied by heat radiation from susceptor
is called “microwave hybrid heating.” In addition, susceptors are always placed symmetrically surrounding the
sample to generate the homogeneous heating.23,24
However, to be useful for the preceding interests,
most microwave apparatus must include a heat generator so-called susceptor, temperature measurement
device, and thermal insulation. These three main parts
are of a great interest to start any successful study in
the microwave processing domain.25 Additionally, the
optimized thermal insulation thickness was also applied
in this work.26 Usually, many workers have used susceptors as additions such as SiC-based ceramics.
Consequently, the present work is mainly focused
on the effect of P2O5 additions on lowering sintering
temperatures and improving the sinterability of diopside specimens using both conventional sintering (CS)
and microwave sintering (MS). Furthermore, a comparison between conventional and MS of diopside compacts is also taken into account.
Besides this, the bioactivity of the abovementioned
diopside samples was also studied. Usually, inductively coupled plasma-optical emission spectroscopy
(ICP-OES) technique is used to verify the like apatite
layer formation. Because ICP-OES uses high purity
(99.9999%) and more expensive gases (Ar), it is replaced
by flame photometer analyzer (FPA), in this work.
To confirm the workability of this proposed simple
and cheap technique, using FPA, a series of samples were investigated using usual techniques such as
UV-Vis spectroscopy, X-ray diffraction (XRD), Fourier
transformed infra-red spectroscopy (FTIR), scanning
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Economic Bioactive Diopside Fabrication
33
electron microscopy (SEM), density and elements solubility measurement.
However, it should be noticed that a correlation
between the microstructure and mechanical properties
of these fabricated bioactive diopside ceramics is also
dictated. This will be the main objective in the second
part of this study.
Materials and Methods
Materials
A high purity SiO2 (99.9%) and a native dolomite
raw material (CaCO3MgCO3) were used as starting
materials to produce the diopside. The purity of this
local dolomite raw material is about 99.5 wt%. Fluorescence XRD analysis showed that dolomite contains
0.27 wt% Fe2O3, 0.07 wt% Al2O3, and 0.02 wt%
NaO2 as impurities. In this work, doloma (CaOMgO)
activated powders by total hydration of MgO and
CaO27 were used, and this raw material may be classified as high-purity calcium and Magnesium oxides
(CaOMgO, 99.0 wt%).28
Processing Methods
The diopside was obtained by a solid-state reaction
from a stoichiometric weighing out the specified quantities of doloma, phase mixture of MgO and CaO, and
pure SiO2. Afterward, the mixtures were wet ballmilled for 4 h, dried, and calcined at 700°C for 2 h.
Different amounts of P2O5 (0.5–5.0 wt%) have been
added to improve the sinterability of the sintered diopside samples. It should be noticed that P2O5 addition
has also been selected because of its good bioactivity.
Then, the powders were uniaxual pressed, using a
steel die at 112 MPa into disks of 13 mm in diameter.
The compacts were, afterward, sintered at different
temperatures ranging between 1100 and 1300°C for
2 h for CS and between 900° and 1125°C for 15 min
for MS (Fig. 1). The heating rate of CS was 6°C/min,
while a maximum rate of about 150°C/min may be
achieved by MS. More details about preparation conditions are reported elsewhere.29
Sintering Techniques
Samples sintering was carried out in air in a 2.45GHz, 850 W modified commercial microwave oven (LG
Fig. 1. Schematic diagram of the microwave setup configuration. (1) Sample, (2) Thermocouple, (3) Microwave heating
element, (4) Thermal insulation, (5) Oven cavity.
MC-805 AY, LG Electronics, Seoul, Korea)25 and conventional (electrical) furnace (LH 30/14, Nabertherm,
Lilienthal, Germany). A schematic diagram of the proposed microwave setup configuration is shown in Fig. 1.
In Vitro Bioactivity Analysis
The selected prepared samples according to their best
sinterability were soaked in SBF, to evaluate the bone-like
apatite formation on surface of sintered granules. These
are diopside samples sintered at 1300°C for 2 h using CS
(D0CS), diopside samples sintered at 1125°C for 15 min
using MS (D0MS), and diopside samples containing
5.0 wt% P2O5 sintered at 1250°C for 2 h using CS
(D5CS). The ion concentrations of the SBF solution were
adjusted to be similar to those in human blood plasma.
The SBF (SBF-K9 type) was prepared by dissolving
reagent-grade CaCl2, NaCl, KCl, MgCl26H2O,
K2HPO43H2O, and NaHCO3 in distilled water. The
SBF solution was buffered at pH 7.4 with (hydroxymethyl)-aminomethane [(CH2OH)3CNH2] and hydrochloric
acid (HCl) according to Kokubo’s protocol.30,31 So, the
“In vitro” test was realized by soaking 10 mg of samples
into 100 mL of SBF at 37°C for times varying from 6 h
to 21 days.
The sampling took place after 6 h, 2, 3, 7, 14,
and 21 days. The experiments were performed in triplicate to ensure the accuracy of results. After each experiment, the samples were separated from the liquids, and
pH of the latter was measured. The reacted sample was
rinsed gently in 10 mL of distilled water for 5 min and
dried in air. The apatite-forming ability of diopside
34
International Journal of Applied Ceramic Technology—Harabi and Zouai
samples was checked by UV-Vis spectroscopy, XRD,
FTIR, and SEM analysis.
A relative weight loss percentage (WL) of diopside
samples after immersion in SBF solutions was calculated from the following equation:
W0 Wt
WL % ¼
100
ð1Þ
W0
where W0 refers to the weight of diopside before immersion
and Wt refers to the weight of diopside after immersion.
A sample having a surface area of 100 mm2 was
placed in 200 mL of an aqueous solution of lactic acid
at pH 4 for 48 h at 37°C, in a constant temperature
bath. Subsequently, the samples were taken out, rinsed,
and dried to measure weight loss.
Characterization Techniques
Many characterization techniques were used to study
the physical and chemical properties of prepared samples.
Mineral phases were identified from peak positions
and intensity using reference data listed in the JCPDSICDD cards. A shape factor is used in XRD and
crystallography to correlate the size of sub-micrometer
particles, or crystallites, in a solid to the broadening of a
peak in a diffraction pattern. In the Scherrer equation,
K k
D¼
ð2Þ
b cos h
where K is the shape factor, k is the X-ray wavelength,
b is the line broadening at half the maximum intensity
(FWHM) in radians, and h is the Bragg angle,32 D is
the mean size of the ordered (crystalline) domains,
which may be equal to the grain size. The dimensionless shape factor has a typical value of about 0.9, but
varies with the actual shape of the crystallite.
UV-Vis spectroscopy is the reliable and accurate
procedure for analysis of samples. UV-Vis spectroscopy
measures the absorption, transmission, and emission of
ultraviolet and visible wavelength by matter. UV-Vis
spectroscopy measures absorption and transmission of
electromagnetic radiations by atoms or molecules. Here,
the band gaps of the samples were calculated to know
the effect of hydroxyl apatite layer on the energy band
of soaked and nonsoaked samples. If some modification
on the surface of the samples was occurred in soaked
samples, it can be verified by UV-Vis spectroscopy
(3101 PC, Shimadzu, Tokyo, Japan). Absorption is the
powerful tool for measuring the band gap of the sam-
Vol. 11, No. 1, 2014
ples. Let the photon beam intensity I0 is incident, the
sample of the thickness is t, and intensity of light transmitted is It, then
It ¼ I0 eat
ð3Þ
a = absorption coefficient
This varies with photon wavelength and also from
material to material.
For direct transition,
aht ¼ A ðht Eg Þn
ð4Þ
where Eg, a, A and n are photon energy, absorption coefficient, constant and 1/2 for allowed transitions, respectively.
For indirect transitions,
aht ¼ A ðht Eg0 Þn
ð5Þ
here, n = 2 for allowed transitions
So, the graph plot of hυ versus (ahυ)2 gives the
value of energy band gap.33
Phase compositions were identified by XRD (D8
Advance, Bruker, Karlsruhe, Germany) with a CuKa
radiation (k = 0.154 nm, filter: Ni, voltage = 40 kV
and current = 30 mA). The JCPDS card number for
diopcide is 02-0663.
Fourier transformed infra-red spectroscopy (Equinox
55, Bruker) was used to highlight the structural analysis.
The microstructure of sample surfaces, after soaking in SBF, was observed using a SEM (JSM-6301 F;
HITACHI, Tokyo, Japan) working at a 7 kV as an
accelerating voltage. Before SEM observation, all samples were gold-coated.
In addition, flame photometer (Jenway PFP7, Bibby
Scientific, Hong Kong, China) technique was used to
evaluate the variations of calcium, magnesium, and
phosphorus concentrations versus soaking time in SBF.
The bulk density was obtained using water displacement.
Results
Sintering of Samples
Conventional Sintering: A preliminary study
showed that the as prepared diopside samples (without
additions) are difficult to sinter, and their relative density did not exceed 86% of theoretical even for samples
sintered at 1250°C for 2 h. To improve both the relative density of the sintered diopside samples, different
amounts of P2O5 (0.5–5.0 wt%) have been added. It
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Economic Bioactive Diopside Fabrication
35
has been found that the sintering temperature is lowered by about 75°C when P2O5 was added. In fact, the
sintering temperature of samples without additions was
decreased from 1300 to 1225°C for samples with P2O5
addition (Fig. 2). For example, the relative density was
increased from 83% TD for sample without addition
to more than 96% TD.
Selected XRD spectra of diopside samples (no
additions), sintered at different temperatures (800–
1300°C) using CS, are shown in Fig. 3. This figure
shows clearly that diopside crystallization is improved
when the sintering temperature is increased.
The effect of P2O5 additions on nucleation and
crystallization is shown in Fig. 4. Selected XRD spectra
of samples containing different amounts of P2O5, heattreated at 740°C for 2 h, are shown in Fig. 4. This figure shows that diopside crystallization begun earlier in
samples containing 2.0 and 5.0 wt% of P2O5, by the
appearance of the more intense peaks of monoclinic
diopside. By contrast, the crystallization of diopside for
samples containing lower percentages ( 0.5 wt%
P2O5) is delayed. Therefore, it can be said that P2O5
additions (for concentrations higher than 0.5 wt%
P2O5) promote diopside crystallization process at a relatively lower temperature (740°C).
Figure 2 illustrates the effect of both sintering temperature and P2O5 additions on the bulk density of compacts. It shows clearly the presence of four main distinct
stages. The first stage is characterized by a slight increase
in relative density. Then, this stage is followed by a second one (from 1150 to 1225°C), which is characterized
by a sharp increase in relative density with increasing
sintering temperature, for all prepared samples. In the
third (intermediate) stage (from 1225 to 1250°C), the
relative density remained nearly constant for all samples,
apart from diopside samples without additions, sintered
at 1250°C. When sintering temperature becomes higher
than 1250°C, a significant decrease in relative density is
obtained, in the final stage (from 1250 to 1275°C).
Fig. 2. Effect of P2O5 additions on sinterability of diopside
samples sintered at different temperatures for 2 h, using conventional sintering (CS).
Fig. 4. X-ray diffraction (XRD) spectra of specimens, containing different percentages of P2O5 (wt%), calcined at 740°C for
2 h, using conventional sintering (CS).
Fig. 3. X-ray diffraction (XRD) spectra of diopside samples
(without additions) sintered at different temperatures for 2 h,
using conventional sintering (CS).
36
International Journal of Applied Ceramic Technology—Harabi and Zouai
Vol. 11, No. 1, 2014
Fourier transformed infra-red spectra of diopside are
shown in Fig. 5. The bands in the region 850–1100 per cm
correspond to the stretching vibrations of the silicate structure,34–36 which is the characteristic of “diopside-type” bands.
Microwave Sintering: When compared with CS,
there was a significant increase in density for samples
sintered using MS. As the MS took a much shorter
time (15 min), densification rate using MS may be
considered to be higher than that of CS. The density
results and X-ray diagrams of samples sintered at different temperatures from 900 to 1125°C for 15 min,
using MS, are shown in Figs. 6 and 7, respectively.
Figure 6 shows that the bulk density is only 55%
theoretical density (TD) for samples sintered at 1100°C
for 2 h, using CS. By contrast, a density level in excess of
93% TD (Fig. 6) has already been achieved at 1100°C
for 15 min, using MS. Also, it can be seen that at the
same temperature, higher densities were achieved using
MS. This suggests that the densification rate in the MS
process was much higher than that in CS. For example, a
high bulk density (approximately 96% TD) was obtained
for diopside containing 5.0 wt% P2O5, sintered at
1225°C for 2 h, using CS, whereas this density level has
been reached when diopside without any addition was
sintered at 1125°C for 15 min, using MS. As would be
expected, the increase in densification ratio of diopside,
using MS, is more obvious than that in the conventionally sintered samples. As the MS took a much shorter
time (<10% of the time of the CS), it can be further suggested that the densification rate (through boundary diffusion) in the CS process was much higher than in the
MS.37 Consequently, diopside ceramics have been successfully and rapidly fabricated by microwave processing.
The heating and time profile of both methods of
heating are shown in Fig. 8. Taking into consideration
the slow heating rate (6°C/min) and the isothermal
holds at intermittent temperatures in a conventional furnace, there is about a 90% reduction in the process time
for the sintering of compacts in a microwave furnace.
The variation of grain size with temperature is shown in
Fig. 9. The average grain size of microwave-sintered pellets is seen to be clearly finer than that of the sintered
pellets by the conventional method at the same sintering
temperature.38 The properties of the materials are determined by their microstructures. It is generally accepted
that a critical issue in microstructural development is
the interplay between densification and coarsening. To
control this microstructural development, parameters
(a)
(b)
(c)
(d)
Fig. 5. Fourier transformed infra-red (FTIR) spectra of diopside samples without additions sintered at 1300°C for 2 h using
conventional sintering (CS) for: (a) before and after soaking in
simulated body fluid (SBF) for (b) 6 h, (c) 2 and (d) 21 days.
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Economic Bioactive Diopside Fabrication
Fig. 6. Comparison between bulk densities of diopside sintered
at different temperatures, using conventional sintering (CS) for
2 h and using microwave sintering (MS) for 15 min.
Fig. 7. X-ray diffraction (XRD) spectra of diopside samples
(without additions) sintered at different temperatures for
15 min, using microwave sintering (MS).
such as sintering temperature, pressure, sintering time,
and heating rate must be optimized. Of all these parameters, rapid heating has reportedly produced beneficial
effects such as high final sintered density for a given
average grain size or fine microstructure compared with
slow heating for similar densities, but conventional fast
firing possesses some difficulties. Differential sintering
that causes differential densification is one of the problems most often encountered in conventional fast firing.
In this context, MS is an alternative technique to overcome the problems of conventional fast firing. Because
37
Fig. 8. Effect of heating modes on the thermal profiles of diopside compacts, using conventional sintering (CS) and microwave
sintering (MS).
Fig. 9. Grain size of sintered diopside pellets as a function of
sintering temperature, using conventional sintering (CS) and
microwave sintering (MS).
it is a noncontact technique and the heat is transferred
to the product via electromagnetic waves, a large
amount of heat can be transferred to the material’s interior minimizing the effects of differential sintering.39
Microstructural development, much finer average grain
size, and higher density achieved in products by MS
result in enhanced mechanical properties with respect to
conventionally treated ones.
Diopside Lactic Acid Attack
Lactic acid is a normal byproduct of muscle metabolism, but it can irritate muscles and cause discomfort and
International Journal of Applied Ceramic Technology—Harabi and Zouai
38
soreness. Muscle soreness associated with exercise is known
as delayed onset muscle soreness (DOMS). DOMS can
make it difficult to walk, reduce your strength, or make
your life uncomfortable for a couple of days.
The effect of P2O5 additions on the decrease in
weight loss ratio of diopside in lactic acid (pH = 4) for
48 h at 37°C is illustrated in Table I. For example, a
considerably low weight loss ratio (0.21%) is obtained
when 5.0 wt% P2O5 has been added into diopside
samples sintered at a relatively lower temperature
(about 1225°C). This value is drastically lower than
those reported, in the literature, for diopside (2.8%)
and HA (16.5%) materials.14
Vol. 11, No. 1, 2014
Physical and Chemical Characterization of Diopside
Without Additions After Soaking in SBF
It should be mentioned that diopside samples sintered at 1300°C for 2 h have been chosen as a reference because of their higher sinterabilities.
Density Measurement: The change in density and
weight loss ratio is a very useful tool in showing the
degree of change in the structure with composition of
the diopside ceramics. The variations of density and
weight loss before and after soaking in SBF are given
in Table II.
Table I. Comparison Between Weight Loss Ratio Values of the Prepared Materials in This Study and for
Those Reported in the Literature
Material
Temperature (°C)
Weight loss (%)
1100
1300
1225
1250
1300
1225
1250
1225
1250
1100
1125
16.5
02.8
1.14 0.06
1.12 0.06
0.24 0.03
0.41 0.09
0.20 0.02
0.21 0.02
0.19 0.01
0.61 0.02
0.22 0.03
HA
Diopside (D)
D (using CS)
D (using CS) + 2 wt% P2O5
D (using CS) + 5 wt% P2O5
D (using MS)
References
14
Present work
CS, conventional sintering; MS, microwave sintering.
Table II. The Change in Density, Weight Loss, Band Gap, and pH After Soaking in SBF of the Prepared
Materials in this Study
Time of immersed in SBF (days)
Material
D0CS
% change in density
Weight loss (%)
Band gap (eV)
pH
D0MS
% change in density
Weight loss (%)
Band gap (eV)
pH
0
1/4
2
3
7
14
21
–
–
1.76
7.4
4.02
+0.93
1.85
7.8
2.89
+0.78
2.19
8.1
1.95
+0.55
2.01
8.0
1.85
+0.41
1.90
7.6
0.6
+0.13
1.73
8.0
+0.28
0.08
1.68
8.0
–
–
1.62
7.4
5.0
+1.10
1.87
7.9
4.05
+0.99
2.02
8.2
3.78
+0.71
1.94
8.1
2.2
+0.42
1.82
8.0
0.7
+0.2
1.69
8.0
+0.19
0.05
1.68
8.0
CS, conventional sintering; MS, microwave sintering; SBF, simulated body fluid.
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Economic Bioactive Diopside Fabrication
The Optical Band Gap Measurement: The optical
band gap of all samples before and after dipping in
SBF solution is calculated using UV-Vis spectroscopy
(Table II). These results will give the information about
the formation of HA layer. If the HA layer is formed,
then there must be change in the band gap of samples.
The optical band gap of the samples may be drawn
from hυ versus (ahυ)2 curves (Fig. 10).
39
of ceramics and ions present in the SBF solution with
time. These chemical reactions result in the formation
of crystalline layer on the surface of D0CS and D5CS
samples as shown in Figs. 11 and 12, respectively.
XRD Analysis: The XRD patterns from all as prepared diopside (D0CS) and soaked in SBF for 6 h, 2,
3, 7, 14, and 21 days possessed the characteristic
hump. The hump presence in XRD pattern confirms
the “amorphous” nature of the sample as shown in
Fig. 11. As the samples dipped in SBF solution, some
chemical reaction takes place between the constituents
(a)
Fig. 11. X-ray diffraction (XRD) patterns of the surfaces of
diopside sintered at 1300°C for 2 h using conventional sintering
(CS) before and after immersion of sintered samples in simulated
body fluid (SBF) for 6 h, 2, 7, 14, and 21 days.
(b)
Fig. 10. Typical variation of (ahυ)2 drawn as a function of
photon energy (optical band gap) for: (a) before and (b) after
soaking in simulated body fluid (SBF) for 2 days.
Fig. 12. X-ray diffraction (XRD) patterns of the surfaces of
diopside containing 5.0 wt% P2O5, sintered at 1250°C for 2 h,
using conventional sintering (CS) before and after immersion of
sintered samples in simulated body fluid (SBF) for 14 days.
International Journal of Applied Ceramic Technology—Harabi and Zouai
40
Evaluation of Bioactivity Using FTIR Spectra: The
in vitro bioactivity of diopside (D0CS) was investigated
for samples after soaking in SBF for 6 h, 2 and
21 days, using FTIR technique as illustrated in Fig. 5.
In the FTIR reflectance spectrum of the D0CS
(Fig. 5c), the characteristic peaks of crystalline apatite
have been evoked after only 2 days of soaking. In
details, the 966-per cm peak (indicating the vibration
40,41
peak of PO3
and the shoulder at 1060 per cm
4 )
(indicating the onset of a Ca-P phase formation)42 can
be attributed to the contribution of carbonated
hydroxyapatite (CHA) to the composite. Additionally,
the broad peak in the 862- to 920-per cm region that
is ascribed to silica vibrations was shifted and sharpened
after the first 2 days, also suggesting the onset of a
CHA phase formation.42
The D0CS sample after dipping in SBF solution
shows the broad hump approximately 3500 per cm due
to the OH group.41 On the other hand, there is no
peak at that region in D0CS samples before dipping in
Vol. 11, No. 1, 2014
SBF solution. Presence of water bands after soaking in
SBF solution ensures the ion exchange process between
hydronium ions from solution and ions from the surface of the D0CS sample. Peaks approximately 1426,
1494 per cm and approximately 866 per cm are due to
42
2
the CO2
respectively, in
3 and PO4 ions in apatite,
soaked samples as shown in Fig. 5d.
Therefore, FTIR results confirm clearly the formation of the CHA layer in D0CS samples after dipping
in the SBF solution.
Microstructural Analysis: Figure 13 summarizes the
SEM micrographs of granule surfaces of three different
groups of samples after soaking in SBF. Firstly, it
shows SEM micrographs of the surfaces of D0CS after
soaking in SBF solution for (a) + (a′) 7 days, (b) + (b′)
14 days, and (c) + (c′) 21 days. It illustrates also SEM
micrographs of sintered granules of D0MS (d) + (d′)
before soaking in SBF solution and (e) + (e′) after
soaking in the SBF solution for 3 days. Finally, (f) + (f′)
(a)
(a′)
(d)
(d′)
(b)
(b′)
(e)
(e′)
(c)
(c′)
(f)
(f′)
Fig. 13. SEM microphotographs of the surfaces of granules sintered at 1300°C for 2 h D0CS after soaking in simulated body fluid
(SBF) solution for (a) + (a′) 7 days, (b) + (b′) 14 days and (c) + (c′) 21 days. SEM micrographs of sintered granules of D0MS
(d) + (d′)before soaking in SBF solution and (e) + (e′) after soaking in the SBF solution for 3 days. (f) + (f′) SEM micrographs of
sintered granules of D5CS after soaking in the SBF solution for 3 days. CS, conventional sintering; MS, microwave sintering.
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Economic Bioactive Diopside Fabrication
SEM micrographs of sintered granules of D5CS after
soaking in the SBF solution for 3 days. In the microstructure after 7 days of soaking as shown in Figs. 13a
and a′, bone-like apatite layers were seen uniformly
deposited on the surface (confirms that surface modifications took place even after 7 days of immersion of
the bulk D0CS in SBF). The formed bone-like apatite
layers grew keeping their shapes after 14 and 21 of days
soaking as illustrated in Figs. 13b and c. The morphology of the bone-like apatite layers is very similar to
those of apatite particles on the surface of bioactive
glasses and glass–ceramics.2,43 To evaluate the ability to
form apatite on diopside ceramics by the MS, samples
of diopside sintered at 1125°C for 15 min were
selected. Figures 13d and e show the SEM micrographs
of diopside samples without additions D0MS before
and after soaking in SBF for 3 days, respectively. After
soaking, the sample surface morphology has been changed, and a layer of dense apatite was formed.
Therefore, on the basis of the results mentioned
above, they are all bioactive. However, this bioactive
ceramics should resist further to acid attack (such as
lactic acid) for many other applications.
Consequently, it can be said that bone-like apatite
formation in SBF was confirmed by XRD, FTIR, and
SEM techniques.
Element Concentrations Analysis: Figure 14 shows
changes in the element concentrations in SBF caused
by immersion of the sintered body of diopside (D0CS,
D5CS and D0MS) as a function of soaking time. In
the early stage of immersion, the calcium content rapidly increased firstly and then decreased rapidly after 2
of days soaking. Moreover, the phosphorous content
minutely decreased with passage of soaking time
because P(V) ions required for apatite formation are
supplied only from the surrounding fluid. In addition,
the magnesium content remained almost unchanged
from beginning to end, which suggests that most portions of Mg(II) ions remained in the sintered body. As
can be seen in the element concentration changes in
SBF, the increase in calcium content is clearly attributed to dissolution of Ca(II) ions from the sintered
body. Thus, the rapid increase in calcium content
might raise the degree of pH and supersaturation of
SBF, which is already supersaturated with regard to
apatite formation even before soaking. Hence, the dissolution of Ca(II) ions from the sintered body makes
apatite nucleation much easier. Hydroxyl groups on the
41
(a)
(b)
(c)
Fig. 14. Variation of Ca, P and Mg concentrations in simulated body fluid (SBF) solution versus soaking times (a) D0CS,
(b) D5CS and (c) D0MS. CS, conventional sintering; MS,
microwave sintering.
surface of artificial materials in contact with the
surrounding fluid are known to act as nuclei for apatite
formation. Ohtsuki et al.44 previously mentioned
that the dissolution of Ca(II) ions from CaO–SiO2
glass produced a silica-rich layer attributed to silanol
(Si–OH) groups on the surface and that the Si–OH
group in the silica-rich layer plays an important role
International Journal of Applied Ceramic Technology—Harabi and Zouai
42
for apatite deposition. It is therefore concluded that the
dissolution of Ca(II) ions from the sintered body in the
early stage of immersion produces a silica-rich layer
having Si–OH groups that effectively induce apatite
nucleation. The pH in SBF bulk solution increased
from a value of 7.4 to approximately 8.1 after 2 days
and remained almost steady during the rest of the
monitoring period of 21 days approximately 8.0
(Table II). As the result of immersion in SBF, preferential dissolution of diopside grains occurred according to
the equation bellow, and Ca and Mg ions were
released.
CaMgðSiO3 Þ2 þ2H2 O ! Ca2þ þ Mg2þ þ 2HSiO2
3
þ 2OH
ð6Þ
As diopside grains dissolved, a porous surface layer
is formed. After this, the surface was completely coated
with nanoglobules of crystal aggregates of Mg-containing calcium-deficient HA (Ca/P = 1.62).45–48
Probably, Si-OH groups existing on the remaining
diopside act as nucleating sites for apatite according to
the following equation:
SiOH
9Ca2þ þ 6HPO2
4 þ OH ƒƒƒƒƒƒ!Ca9 ðHPO4 Þ
ðPO4 Þ5 ðOHÞ þ 5Hþ
ð7Þ
Discussion
As far as sintering is concerned, one can distinguish clearly the huge difference between the two proposed processes (CS and MS) described before; the
bulk density of diopside samples sintered at 1150°C
for 2 h is <59% TD, using the CS. In contrast to this,
a bulk density about 96% TD is achieved for diopside
samples sintered at 1125°C for 15 min according to
the second process (MS), under the same conditions
and without any addition. Also, it can be seen that at
the same temperature (1100°C), higher densities were
achieved using MS. This suggests that the densification
rate in the MS process was much higher than that
using CS.
The high rate of sintering during the first stage
for samples containing 2 and 5 wt% P2O5 confirms
the significant effect of this addition on the liquid-
Vol. 11, No. 1, 2014
phase formation. Therefore, the liquid-phase sintering
mechanism is evident, even though several mechanisms
may be distinguished, by which the liquid phase
contributes to its sintering. Additionally, the presence
of the liquid phase may lead to the re-arrangement of
atoms and becoming consequently more mobilized.
The presence of the liquid phase may also encourage
small particles to move through it toward the concavity
regions of larger granules or particles to promote
grain growth and therefore greater densification of the
material.
However, the semi-stability observed in the second
stage may be due to the fact that sintering reached its
final stage, where the formed pores were closed, and
the increase in temperature cannot increase further the
sintering rate. Moreover, the sintering temperature of
diopside ceramics is lowered by the addition of 5 wt%
P2O5. Because of its lower melting temperature, P2O5
may promote sintering of diopside. By contrast, the
addition of 2 and 5 wt% P2O5 decreases the rate of
sintering (during the third stage). This decrease may be
due to the formation of an excessive liquid phase. In
fact, the increase in sintering temperature may encourage excessive formation of the liquid phase, which
inhibits sintering in its turn. In addition, higher sintering temperatures may lead to the exit of some gases
(like oxygen) involved in the chemical composition of
raw materials. So, this is may be the main factor controlling this decrease in sintering rate. However, one
can attribute this decrease to diopside decomposition.
This interpretation may also be discarded because of its
structure stability in all sintered samples at the last
stage.
The weight loss of D0CS (0.24%) and D0MS
(0.22%) in lactic acid is much lower than that of HA
(16.5%). A significant effect of sintering temperatures
on the weight loss ratio is only observed for samples
containing 2.0 wt% P2O5. This may be due to the fact
that the relative density is about the same for each
composition (0.0 and 5.0 wt% P2O5), sintered at 1225
and 1250°C. However, the difference in weight loss
ratio observed for 2.0 wt% P2O5 addition may be
attributed to the difference in relative density of the
two samples.
Even though available data, in this work, are not
sufficient yet to find out the sintering mechanisms, it
can be said that the densification may mainly be controlled by a liquid-phase sintering. This is due to a possible liquid-phase formation by the reaction between
www.ceramics.org/ACT
Economic Bioactive Diopside Fabrication
P2O5 and SiO2, MgO and/or CaO. Consequently, the
presence of an intergranular liquid phase may inhibit
samples etching by lactic acid (0.21%).
When a bioactive material is implanted in the living tissue such as bone, it combines with them with
formation of bone-like apatite layer on their surfaces.
Hence, the apatite layer formation on the surface of
diopside is a prerequisite for the bioactivity and its
direct bonding property to the living bones. The in
vitro bioactivity analysis by immersion in SBF solution
revealed the presence of apatite formation in diopside
samples. However, the results presented here have been
mainly explained with an emphasis on diopside due to
their high potential for use in human medicine. The
samples Eg increase after soaking in SBF solution for
6 h and 2 days. By contrast, samples Eg decrease for
the remaining soaking periods (3, 7, 14 and 21 days)
after dipping in SBF solution. By comparing these
results with XRD results, it can be said that CHA
layers are formed on fabricated samples. This CHA
formation is explained by the decrease in band
gap. The formation of crystalline HA layer samples
reduces the porosity and increases the ordering, which
lead to the decrease in band gap. As shown in Table II,
those samples show higher weight loss ratios. The
density of this sample decreases after dipping in SBF
solution. It indicates that these samples became more
porous due to higher rate of leaching. This leads to
more amorphization in these samples. Therefore, the
optical band gap increases after immersing samples in
SBF. Optical band gap in amorphous solids can be
explained as the width of the localized states near the
mobility edge which in turn depends on the degree of
disorder and defects present in amorphous structure.
The XRD patterns observed for samples D0CS and
for D5CS (i.e., before soaking in SBF solution; Figs. 11
and 12, respectively) coincide well with that of diopside
phase. This observation is in a good agreement with that
of reference.15,16,49 However, the XRD of investigated
diopside after soaking in SBF solution for time durations varying between 6 h and 21 days (Fig. 11)
showed considerable differences in comparison with the
diffractograms of their respective parent diopside. A
small X-ray peak at 2h = 31.77° corresponding to the
formation of crystalline CHA can be seen for diopside
after immersion in SBF for 2 days (Fig. 11). In addition, in case of D5CS, crystalline phase could be
observed in XRD patterns of diopside samples soaked in
SBF solution for 14 days, indicating the formation of
43
CHA on the surface of CaMgSi2O6 samples (Fig. 12).
It is obvious that the characteristic peaks of CaMgSi2O3
decreased after 6 h of soaking, where the bands became
smoother after immersion in SBF. Furthermore, the
XRD pattern for diopside depicted a broad amorphous
halo after 6 h of immersion in SBF (Fig. 11), while the
FTIR spectra of this D0CS (Fig. 5) exhibited significant
structural differences before and after immersion in
SBF. As is evident from Fig. 5b, strong low-frequency
band centered at 1070 per cm, ascribed to a deformation mode of silica layer that develops on the dissolving
diopside particles, could be seen in ceramics after
immersion in SBF solution for 6 h. Further, the band
at 1426 per cm along with another one at 1494 per cm
presents in diopside ceramics after immersion in SBF
solution for 2 days corresponds to incorporation of carbonate into the apatite, resulting in CHA, rather than
stoichiometric HA.50 Furthermore, two bands were
observed (Fig. 5c) at 966 per cm after immersion in
SBF solution for 2 days. This is the most characteristic
region for apatite and other phosphates as it corresponds
to P–O bending vibrations in a PO3
4 tetrahedron. A
single peak in this region suggests the presence of nonapatite or calcium phosphate, which may also be considered as an indication for the presence of precursors to
HA.42 However, apart from a band at 966 per cm as is
evident in Fig. 5c, no other bands in this region could
be observed for diopside ceramics, even after 21 days of
immersion in SBF solution. Figure 13 illustrates the
morphologies of diopside samples (D0CS) after soaking
in SBF solution for 7 (Figs. 13a and a′) and 14 days
(Figs. 13b and b′); it can be seen that the surface of
diopside samples was clearly covered by the bone-like
apatite layers (Fig. 13). The obtained SEM images of
immerged granules are shown in Fig. 13. Images
of D0CS-soaked granules (Fig. 13a) showed that, after
7 of days exposure to SBF, the bone-like apatite was not
formed. However, after 14 and 21 days, the surface of
D0CS granules was covered with a uniform thick layer
of calcium phosphate. However, in D0MS and D5CS, it
can be pointed out that a calcium phosphate phase was
already formed after 3 of days soaking time earlier than
in the case of pure D0CS. This result confirms well the
beneficial effect of P2O3 additions on sinterability, crystallization and bioactivity of sintered diopside samples.
Moreover, one can observe in D5CS that their grains
are turning elongated as shown in Fig. 13f.
The evolution of the ionic concentrations in SBF
solutions along the time of immersion of the samples
44
International Journal of Applied Ceramic Technology—Harabi and Zouai
was also monitored in this study. Figure 14 reports the
data for the diopside sample (D0CS, D5CS and
D0MS), as an example. At the first stage, the ceramic
released Ca and Mg ions. It can be seen that the concentrations of both Mg and Ca firstly increase and
then tend to achieve constant values after 6 h of
immersion. The concentration of Ca increased slightly
from 100 to 126 ppm for 2 days of incubation for
D0CS. Mg ion concentrations increased very slightly
from 36 to 44 ppm for the same period, probably due
to preferential dissolution of diopside granules occurred
according to Eq. (6), and Ca and Mg ions were
released. As diopside granules dissolved, a porous surface
layer is formed.
However, the concentration of Mg, Ca, and P ions
diminished during the second stage. This decrease is
consistent with the observed deposition of an apatite
layer onto the surface of the porous samples and with
the establishment of an apparent equilibrium situation,
with the rate of depositions being roughly balanced by
the rate of dissolution of the solid. On the other hand,
the P concentration seems to decrease up to the end
of the 14 days (along the experiment), which might be
due to adsorption effects on the surface of the solid
phase. This last decrease might be due to the nucleation of a calcium-deficient CHA layer (Eq. 7).
Mg has been attributed a significant impact on the
mineralization process and some influence in the CHA
crystal formation and growth.51 Additionally, the deficiency of Mg in bone has been suggested as a possible
risk factor for osteoporosis in humans.52 Therefore, the
data shown in Fig. 14 suggest that the tested material
is able to release most of the essential elements in the
physiological fluids. This together with the ability to
direct bond to the hard tissues makes the material very
promising for biomedical applications. The changes in
the element concentrations in SBF caused by immersion of the prepared diopside sample using MS
(D0MS) specimen after soaking in SBF for 6 h, 2, 3,
7, and 14 days are shown in Fig. 14. The P concentration seems to decrease along the experiment. Therefore,
it also can be concluded that the phase of lath-like layer
is mainly CHA.
The experimental results of Mezahi et al.6 showed
that dissolution-precipitation kinetics of N-HA is activated with the sintering temperature. However, Tampieri et al. and Bonfield found that the mechanism of
bone-like apatite precipitation is activated when the
porosity ratio is increased.53,54 In addition, Niwa55 has
Vol. 11, No. 1, 2014
documented that the ability of bone integration of HA
decreases as its sintering temperature increases. Then,
Kim et al.56 have demonstrated that the sintering temperature of HA not only influences the formation
mechanism of bone-like apatite but also affects the rate
of formation of biologically active bone-like apatite on
its surface. A comparison between the results of pure
diopside D0CS and of D5CS and D0MS samples allows
to conclude that the presence of P2O5 addition and
prepared ceramics by the MS activates the formation of
bone-like apatite. The formation time or period needed
for the bone-like apatite decreased from more than 7 to
3 days (Fig. 13). Furthermore, the Ca and P amounts,
kept out from SBF to surface of D5CS and D0MS,
were greater than those of the same elements kept out
from SBF to surface of D0CS (Fig. 14).
The apatite-forming mechanism on the diopside as
proposed is schematically represented in Fig. 15. The
mechanism of CHA layer formation on diopside
ceramics can be summarized in the following steps:
When the diopside is immersed in SBF, dissolution
of diopside in SBF with release of Ca(II) and Mg
(II) ions in it exchange with H+ in SBF solution
leading to the formation of silica-rich layer attributed to silanol (Si-OH) in the surface layer, an
increase in the pH value at the diopside-SBF, and
eventually the production of a negatively charged
surface with the functional group (Si-O-). The Ca
(II) ions in SBF solution are first attracted to the
interface between diopside and solution, and consequently, the ionic activity product of the apatite in
the interface is high enough to precipitate apatite on
the surface of diopside samples. The ionic dissolution products (Ca(II) ion) showed a range of concentration that will lead to enhanced proliferation of
osteoblast (osteostimulation).
Next, the nucleation of a calcium-deficient HA layer
takes place on the porous surface of the material, by
reaction of SBF phosphate ions with the excess of
Ca(II) ions liberated to SBF by the ceramic. The
silicate ions liberated by the ceramic can produce a
silicon HA.
Once apatite nuclei are formed on the surface of the
porous layer, they can grow spontaneously by consuming calcium and phosphate ions from the surrounding SBF.
Finally, replacing ICP-OES technique by FPA
and/or UV-Vis spectroscopy was confirmed, in this
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Economic Bioactive Diopside Fabrication
45
addition. By addition of P2O5, sintering temperature
was lowered by about 75°C (from 1300 to 1225°C). A
relative density higher than 96% was reached for samples sintered, only, at 1225°C for 2 h, using CS and
containing 5 wt% P2O5.
It has been confirmed that the advantage of using
MS is the rapidity of sintering (15 min) when compared with CS. For example, at 1275°C (120 min), the
relative densities of samples using CS were about 94%
(120 min) and for MS were about 96% at 1125°C
(15 min). Another important result is that the P2O5
additions decrease considerably the weight loss ratio of
diopside samples in aqueous solution of lactic acid
from 1.12% to 0.19% (about six times better) for samples with 5 wt% P2O5 sintered at 1250°C for 2 h.
Finally, the CHA was formed and covered the surface of pure diopside samples soaked in SBF solution
for 2 days. Therefore, the diopside samples show an
excellent bioactivity and may be considered as an excellent candidate in biomaterials applications.
Because ICP uses high purity (99.9999%) and
expensive gases (Ar), it was successfully replaced by
FPA in this study. Furthermore, the prepared samples
were investigated using usual techniques such as
UV-Vis spectroscopy, XRD, FTIR, SEM, density and
elements solubility measurement, to confirm the results
obtained by this proposed simple and cheap technique.
This work is in progress to study in more details
the mechanical properties of these fabricated bioactive
diopside samples. A correlation between these mechanical properties and microstructure of the fabricated samples will also be studied.
Fig. 15. Schematic drawing summarizing the proposed mechanism of apatite layer formation.
work, to verify the bone-like apatite layer formation.
Indeed, these two techniques were applied without any
need to use usual techniques such as UV-Vis spectroscopy, XRD, FTIR, SEM, density and elements solubility measurement.
Conclusions
A new and economic approach to synthesize and
fabricate bioactive diopside ceramics using a modified
domestic microwave oven was proposed. Besides this,
the relative density of diopside samples was closely
related to both sintering temperatures and P2O5
References
1. L. L. Hench, R. J. Splinter, W. C. Allen, and T. K. Greenlee, “Mechanisms of Interfacial Bonding Between Ceramics and Bone,” J. Biomed.
Mater. Res., 2 117–141 (1971).
2. M. A. Sainz, P. Pena, S. Serena, and A. Caballero, “Influence of Design
on Bioactivity of Novel CaSiO3–CaMg(SiO3)2 Bioceramics: In Vitro Simulated Body Fluid Test and Thermodynamic Simulation,” Acta Biomater.,
6 2797–2807 (2010).
3. K. Ohura, et al., “Bone-Bonding Ability of P2O5-Free CaO_ SiO2
Glasses,” J. Biomed. Mater. Res., 25 357–365 (1991).
4. S. Kotani, et al., “Bone Bonding Mechanism of b-Tricalcium Phosphate,”
J. Biomed. Mater. Res., 25 1303–1315 (1991).
5. L. L. Hench, “Bioceramics: From Concept to Clinic,” J. Am. Ceram. Soc.,
74 1487–1510 (1991).
6. F. Z. Mezahi, et al., “Dissolution Kinetic and Structural Behaviour of Natural Hydroxyapatite vs. Thermal Treatment,” J. Therm. Anal. Calorim., 95
21–29 (2009).
7. A. Harabi, D. Belamri, N. Karboua, and F. Z. Mezahi, “Sintering of Bioceramics Using a Modified Domestic Microwave Oven: Natural
Hydroxyapatite Sintering,” J. Therm. Anal. Calorim., 104 283–289 (2011).
46
International Journal of Applied Ceramic Technology—Harabi and Zouai
8. L. L. Hench and J. Wilson, “An Introduction of Bioceramics;” Advanced
Series in Ceramics, Vol. 1. eds., L. L. Hench and J. Wilson. World Scientific Publishing, Singapore, 1–24, 1993.
9. F. Bouzerara, A. Harabi, S. Achour, and A. Larbot, “Porous Ceramic Supports for Membranes Prepared From Kaolin and Doloma Mixtures,”
J. Eur. Ceram. Soc., 26 1663–1671 (2006).
10. A. Harabi and F. Bouzerara, “Fabrication of Tubular Membrane Supports
From Low Price Raw Materials, Using Both Centrifugal Casting and/or
Extrusion Methods;” Chap 13. Expanding Issues in Desalination, ed., R. Y.
Ning. INTECH Open Access, Rijeka, Croatia, 253–274, 2011.
11. W. Chengtie, R. Yoghambha, and Z. Hala, “Porous Diopside (CaMgSi2O6) Scaffold: A Promising Bioactive Material for Bone Tissue Engineering,” Acta Biomater., 6 2237–2245 (2010).
12. C. Wu and J. Chang, “In Vitro Bioactivity of Akermanite Ceramics,”
J. Biomed. Mater. Res., 76 [1] 73–80 (2006).
13. S. Nakajima, Y. Kurihara, Y. Wakatsuki, and H. Noma, “Physiochemical
Characteristics of New Reinforcement of Ceramic Implant,” Shikwa Gakuho, 90 [1] 525–553 (1990).
14. T. Nonami and S. Tsutsumani, “Study of Diopside Ceramics for Biomaterials,” J. Mater. Sci. Mater. Med., 10 [8] 475–479 (1999).
15. Y. I. Noriyuki, L. Geun-Hyoung, T. Yoshikazu, and K. Norimichi,
“Sintering Behavior and Apatite Formation of Diopside Prepared by CoPrecipitation Process,” Colloids Surf. B, 34 239–245 (2004).
16. Y. I. Noriyuki, L. Geun-Hyoung, T. Yoshikazu, and K. Norimichi, “Preparation of Diopside With Apatite-Forming Ability by Sol–Gel Process
Using Metal Alkoxide and Metal Salts,” Colloids Surf. B, 33 1–6 (2004).
17. A. Ibanez, J. M. G. Pena, and F. Sandoval, “Solid-State Reaction for Producing b-Wollastonite,” Ceram Bull, 69 374–378 (1990).
18. K. Lin, J. Chang, G. Chen, M. Ruan, and C. Ning, “A Simple Method to
Synthesize Single-Crystalline b-Wollastonite Nanowires,” J. Cryst. Growth,
300 267–271 (2007).
19. D. E. Clark, D. C. Folz, E. C. Folgar, and M. M. Mahmoud, Microwave
Solution of Ceramic Engineering, The American Ceramic Society, Westerville,
OH, 2005.
20. D. Atong and D. E. Clark, “Ignition Behavior and Characteristic of
Microwave—Combustion Synthesized Al2O3–TiC Powders,” Ceram. Int.,
30 1909–1912 (2004).
21. D. Atong and D. E. Clark, “Microwave-Induced Combustion Synthesis of
TiC–Al2O3 Composites,” Ceram. Eng. Sci. Proc., 20 111–118 (1999).
22. D. Atong and D. E. Clark, “Synthesis of TiC–Al2O3 Composites Using
Microwave Induced Self Propagating High Temperature Synthesis (SHS),”
Ceram. Eng. Sci. Proc., 19 415–421 (1998).
23. C. Zhao, J. Vleugels, C. Groffils, P. J. Luypaert, and O. Van der bliest,
“Hybrid Sintering With a Tubular Susceptor in a Cylindrical Single-Mode
Microwave Furnace,” Acta Mater., 48 3795–3801 (2000).
24. P. D. Ramesh, B. David, and L. Schachter, “Use of Partially Oxidized SiC
Particle Bed for Microwave Sintering of Low Loss Ceramics,” Mater. Sci.
Eng., A, 266 211–220 (1999).
25. A. Harabi, N. Karboua, and S. Achour, “Higher Temperatures Microwave
Heating Element (~1550°C),” (Element Chauffant a Micro-Onde a Haute
Temperature (~1550°C)) Patent 8 pages, INAPI N°.110207, Algeria,
2011.
26. A. Harabi, N. Karboua, and S. Achour, “Effect of Thickness and Orientation of Alumina Fibrous Thermal Insulation on Microwave Heating in a
Modified Domestic 2.45 GHz Multi-Mode Cavity,” Int. J. Appl. Ceram.
Technol., 9 [1] 124–132 (2012).
27. A. Harabi and S. Achour, “A Process for Sintering of MgO and CaO
Based Ceramics,” J. Mater. Sci. Lett., 18 955–957 (1999).
28. W. Ming, Z. Ruzhong, M. Weiqing, and L. Yi, “Sol–Gel Derived CaO–
SiO2–B2O3 Glass/CaSiO3 Ceramic Composites: Processing and Electrical
Properties,” J. Mater. Sci.: Mater. Electron., 22 843–848 (2011).
29. A. Harabi and S. Zouai, “A Preparation Process of Bioactive Diopside
From Native Dolomite and SiO2,” Patent, INAPI N°.110726, Algeria,
2011.
30. T. Kokubo, H. Kushitani, S. Sakka, T. Kitsugi, and T. Yamamuro, “Solutions Able to Reproduce in Vivo Surface-Structure Changes in Bioactive
Glass-Ceramics A-W,” J. Biomed. Mater. Res., 24 721–734 (1990).
31. S. B. Cho, K. Nakanishi, T. Kokubo, N. Soga, C. Ohtsuki, and
T. Nakamura, “Dependence of Apatite Formation on Silica-Gel on its
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
52.
53.
54.
55.
56.
Vol. 11, No. 1, 2014
Structure—Effect of Heat Treatment,” J. Am. Ceram. Soc., 78 1769–
1774 (1995).
B. D. Cullity, Elements of X-Ray Diffraction, 2nd ed., Addison-Wesley,
Boston, MA, 1978.
A. Hafdallah, F. Yanineb, M. S. Aida, and N. Attaf, “In Doped ZnO Thin
Films,” J. Alloy. Compd., 509 7267–7270 (2011).
E. V. Kalinkina, A. M. Kalinkin, W. Forsling, and V. N. Macarov, “Sorption of Atmospheric Carbon Dioxide and Structural Changes of Ca and
Mg Silicate Minerals During Grinding I. Diopside,” Int. J. Miner. Process.,
61 273–288 (2001).
V. E. Hamilton, “Thermal Infrared Emission Spectroscopy of the Pyroxene
Mineral Series,” J. Geophys. Res., 105 9701–9716 (2000).
G. Ashutosh, U. T. Dilshat, K. G. Ishu, R. S. Essam, and M. F. F Jose,
“Effect of BaO on the Crystallization Kinetics of Glasses Along the Diopside–Ca-Tschermak Join,” J. Non. Cryst. Solids, 355 193–202 (2009).
Y. Fang, D. K. Agrawal, M. R. Della, and R. Rustum, “Microwave Sintering of Hydroxyapatite Ceramics,” J. Mater. Res., 9 180–187 (1994).
J. H. Yang, et al., “Microwave Process for Sintering of Uranium Dioxide,”
J. Nucl. Mater., 325 210–216 (2004).
R. R. Menezes and R. H. G. A. Kiminami, “Microwave Sintering of Alumina–Zirconia Nanocomposites,” J. Mater. Process. Technol., 203 513–517
(2008).
“Combustion Synthesis of Calcium Phosphate Bioceramic
T. A. CuE,
Powders,” J. Eur. Ceram. Soc., 20 2389–2394 (2000).
B. Mihailova, B. Kolev, C. Balarew, E. Dyulgerova, and L. Konstantinov,
“Vibration Spectroscopy Study of Hydrolyzed Precursor for Sintering Calcium Phosphate Bio-Ceramics,” J. Mater. Sci., 36 4291–4297 (2001).
E. Roumeli, et al., “Study of the Bioactive Behavior of Hydroxyapatite/
SiO2–CaO–MgO Glass-Ceramics Synthesized by Transferred Arc Plasma
(TAP),” J. Int. Soc. Ceramics Med., 1 1–4 (2011).
G. Mestres, C. L. Van, and M. P. Ginebra, “Silicon-Stabilized a-Tricalcium Phosphate and its Use in a Calcium Phosphate Cement: Characterization and Cell Response,” Acta Biomater., 8 1169–1179 (2012).
C. Ohtsuki, T. Kokubo, and T. Yamamuro, “Apatite-Forming Ability of
CaO-Containing Titania,” J. Non-Cryst. Solids, 143 84 (1992).
A. Ravaglioli, A. Krajewski, V. Biasini, R. Martinetti, C. Mangano, and
G. Venini, “Interface Between Hydroxyapatite and Mandibular Human
Bone Tissue,” Biomaterials, 13 162–167 (1992).
Z. B. Luklinska and W. Bonfield, “Morphology and Ultrastructure of the
Interface Between Hydroxyapatite–Polyhydroxybutyrate Composite
Implant and Bone,” J. Mater. Sci. Mater. Med., 8 379–383 (1997).
P. N. De Aza, Z. B. Luklinska, M. R. Anseau, F. Guitian, and S. De Aza,
“Transmission Electron Microscopy of the Interface Between Bone and
Pseudo Wollastonite Implant,” J. Microsc. Oxford, 201 33–43 (2001).
R. G. Carrodeguas, E. Cordoba, A. H. De Aza, S. De Aza, and P. Pena,
“Bone-Like Apatite-Forming Ability of Ca3(PO4)2-CaMg(SiO3)2 Ceramics
in Simulated Body Fluid,” Key Eng. Mater., 396–8 103–106 (2009).
I. Kansal, D. U. Tulyaganov, A. Goel, M. J. Pascual, and M. F. J.
Ferreira, “Structural Analysis and Thermal Behavior of Diopside–Fluorapatite–Wollastonite- Based Glasses and Glass–Ceramics,” Acta Biomater., 6
4380–4388 (2010).
G. Lusvardi, G. Malavasi, L. Menabue, V. Aina, and C. Morterra, “Fluoride-Containing Bioactive Glasses: Surface Reactivity in Simulated Body
Fluids Solutions,” Acta Biomater., 5 3548–3562 (2009).
C. Ergun, T. J. Webster, R. Bizios, and R. H. Doremus, “Hydroxylapatite
With Substituted Magnesium, Zinc, Cadmium, and Yttrium. I. Structure
and Microstructure,” J. Biomed. Mater. Res., 59 [2] 305–311 (2002).
R. K. Rude, “Magnesium Deficiency: A Cause of Heterogeneous Disease
in Humans,” J. Bone Miner. Res., 13 [4] 749–758 (1998).
A. Tampieri, G. Celotti, S. Sprio, A. Delcogliano, and S. Franzese, “Porosity-Graded Hydroxyapatite Ceramics to Replace Natural Bone,” Biomaterials, 22 [11] 1365–1370 (2001).
W. Bonfield, “Designing Porous Scaffolds for Tissue Engineering,” Philos.
Transact. A Math. Phys. Eng. Sci., 364 227–232 (2006).
J. Niwa, “Acceleration of Bone-Repair Using Hydroxyapatite,” Bone Fracture, 5 124–128 (1983).
H. M. Kim, T. Himeno, T. Kokubo, and T. Nakamura, “Process and
Kinetics of Bonelike Apatite Formation on Sintered Hydroxyapatite in a
Simulated Body Fluid,” Biomaterials, 26 4366–4373 (2005).