Journal of Minerals & Materials Characterization & Engineering, Vol. 9, No.8, pp.683-692, 2010 Printed in the USA. All rights reserved
Synthesis of Hydroxyapatite Bio-Ceramic Powder by Hydrothermal Method
P. Hui, S.L. Meena, Gurbhinder Singh*, R.D. Agarawal, Satya Prakash
Metallurgical and Materials Engineering Department, Indian Institute of Technology Roorkee,
Hydroxyapatite bio-ceramic powder was synthesized using waste eggshells as calcium source by
a straight forward thermal method. The process is carried out at high temperature. Different
calcium phosphate phases were obtained just by changing the thermal treatment. HAp is the only
apatite present in the reaction products, along with minute fractions of other calcium
compounds. The final product was characterized by X-ray diffraction, Scanning electron
microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FT-IR). Thermal analysis
(TG–DTA) was carried out to investigate the thermal stability of HAp.
Keywords: Hydroxyapatite, eggshell, X-ray diffraction, FT-IR, TG-DTA
Hydroxyapatite (HAp) is one of the most versatile materials used for implantation purpose due to
its similarity to natural bone material [1].HAp has approximate chemical formula
Ca10(PO4)6(OH)2 or Ca5(PO4)3(OH) , and is the main inorganic constituent of bones in humans.
Synthetic HAp has been successfully used in hard tissue surgery, as it is capable of undergoing
bonding osteogenesis and is relatively insoluble in vivo [2]. It is a particularly attractive material
for bone and tooth implants since it closely resembles human tooth and bone mineral and has
proven to be biologically compatible with these tissues [3-5]. Many studies have indicated that
HAp ceramics show no toxicity, inflammatory response, pyrogenetic response. It has excellent
fibrous tissue formation between implant and bone, and has the ability to bond directly to the
684 P. Hui, S.L. Meena, G. Singh, R.D. Agarawal, S. Prakash Vol.9, No.8
host bone [3]. Hydroxyapatite (HAp) and other calcium phosphate (CaP) materials exhibit
excellent bioactive and osteoconductive properties because of their similarity to natural bone
material. HA coating promotes a direct physiochemical bond with bone, which leads to more
rapid implant fixation and the development of a stable bone biomaterial interface [6]. Despite the
proven ability of HAp to promote bone attachment, long term performance is limited by
problems like coating adhesion, rapid dissolution (subsequent loss of bone –bonding), fatigue
failure and the creation of particulate debris [7].
Several methods of chemical synthesis have been developed to prepare HAp using various types
of Ca and P sources [8-11]. In the present synthesis process, an attempt has been made to
synthesize pure and biocompatible HAp powder by using hen’s eggshell as the calcium source.
The eggshell represents 11% of the total weight of the egg and is composed of calcium carbonate
(94%), calcium phosphate (1%), organic matter (4%) and magnesium carbonate (1%).
Egg-shells of hen were collected in bulk. They were cleaned mechanically by de - ionized water
and boiled in water for 20 minutes. They were then placed in a furnace for a three-stage thermal
treatment. Heating rate and soaking time at these three stages are given in Table I. Experimental
setup for this synthesis is shown in Fig. 1.
Table I: Three stage thermal treatment of egg-shell
Fig. 1 : Experimental setup for CaO synthesis
In first stage the eggshell heated upto 450 0C at the heating rate 70C/min. followed by soaking for
two Hrs at 4500C. Similarly in second stage eggshells were heated from 450-6000C at heating
e Temperature
rate /min Soakin
Time (Hrs)
Stage 1 0-45
Stage 2 450-60
Stage 3 600-90
Vol.9, No.8 Synthesis of Hydroxyapatite 685
rate 50C/min. and soaking at 6000C for two Hrs. In final stage the eggshell heated from 6000C to
9000C at the heating rate of 40C/min followed by soaking for one Hr at 9000C.
At the temperature 9000C, the eggshells transformed into calcium oxide by releasing carbon
dioxide (CO2) according to the following equation:
CaCO3 CaO + CO2
The CaO so obtained from the eggshells was then converted into HAp in a phosphate solution
following a procedure reported before by Roy [12], Eric M. Rivera [8] and subsequently
used by others [13].
A stoichiometric amount of calcined eggshell was dispersed in well-degassed distilled water.
Under vigorous stirring reagent grade tri-calcium phosphate solution (Merck) was mixed into
calcined eggshell solution at a controlled into the suspension maintained at 900C temperature.
Mixing was continued for more time to achieve proper mixed solution. After completion of
mixing, the solution was subjected to aging treatment for 24 Hrs and then filtered. The filtered
solution was further heat treated in presence of steam atmosphere. The rate of heating was
150C/min. up to 6500C, 80C/min from 6500C to 9000C followed by soaking for 1 Hrs at
9000C.Steam is supplied to maintain H2O presence during reaction. The expected reaction is
given as:
3Ca3(PO4)2+CaO+H2O Ca10(PO4)6(OH)2
As the synthesized powder obtained from eggshell contain few parts of calcium hydroxide along
with calcium oxide so other probable reaction is
3Ca3(PO4)2+Ca(OH)2 Ca10(PO4)6(OH)2
686 P. Hui, S.L. Meena, G. Singh, R.D. Agarawal, S. Prakash Vol.9, No.8
Fig. 2: The XRD of Calcium oxide (CaO) produced from Egg Shell
2.1 Characterization of the Product
X-ray diffraction analysis of the product in Fig. 2 shows intensity peaks corresponding to JCPDS
37-1497 files for CaO, with some fraction of other species Ca(OH)2, CaCO3.The observed
change in the weight corresponds to loss of gaseous CO2 .
The X-ray powder diffraction (XRD) analysis of the synthesized HAp samples was done (Bruker
D-8 Advanced, Germany) in reflection mode with Cu Kα (λ=1.5405 Å) radiation. The data were
analyzed in the 2Ө range from 10º to 80º with a scanning step of 2º per min. The results reveal
that the thermal processing of CaO in the phosphate solution at 9500C produces a solid material
of white color with porous structure having pores of irregular diameter and high mechanical
strength. X-ray diffraction of this sample in Fig. 3 shows several phases. The crystalline phases
was identified as HAp (JCPDS, 9-0432), with some phases of calcium oxide (JCPD, 37-1497).
and calcium hydroxide (JCPDS,4-0733). These phases may be attributed to incomplete
transformation of calcite, resulting from interruption in supply of steam atmosphere at the high
temperature during reaction process.
The functional groups present in HAp were ascertained by Fourier transform infrared
spectroscopy (FT-IR) Thermo NICOLET 5700, FTIR. The FT-IR spectra were obtained over the
region 400–4,000 cm-1 using KBr pellet technique with spectral resolution of 4 cm-1.
20 40 60 80100
- CaO
2 Theta
Vol.9, No.8 Synthesis of Hydroxyapatite 687
The TG–DTA analysis was done with An Perkin Elmer (Pyris Diamond) thermal analyzer. The
weight loss and thermal stability of the samples were also evaluated from the thermo gravimetric
analysis data. The heating rate of 100C/min was employed upto temperature 14000C in air
Fig. 3: The XRD of synthesized HA
20 40 60 80
* HAp
# Ca(OH)
0 CaO
688 P. Hui, S.L. Meena, G. Singh, R.D. Agarawal, S. Prakash Vol.9, No.8
Fig.4: FT-IR spectrum of synthesized HAp
The FT-IR spectrum of the HAp produced by hydrothermal method shown in Fig.4 shows all the
characteristic bands for Hydroxyapatite [14, 15]. The asymmetric stretching (v3) and bending
(v4) modes of PO4-3 ion were detected at around 1047.9, and 604.1 and 566.7 cm1, respectively.
The symmetrical stretching modes (v1 and v2) of PO4-3 ion were also found at around 961.4 and
470.4 cm1, respectively.
The liberation and stretching mode of the OH were detected at around 3571 and 1637cm1,
respectively. The stretching vibrations, ascribed to CO32 at around 1425.1, and 876cm1 were
also present [16]. The bands at 3413.3 and 1637.5cm–1 correspond to adsorbed H2O.
XRD patterns of HAp shown in the Fig.3, shows a broad reflection peak in the range of 31.8-
32.50 of 2Ө values, which corresponds to the characteristic peak of apatite phase (according to
JCPDS card # 9-432).
Analysis of the SEM micrographs presented in Fig. 6 shows that the synthesized HAp consisted
of agglomerates. The shapes of which were almost the same and the size was always between
3µm and 5µm, built up from fine particles about 400 nm in size. Individual fine particles with
spherical and semi-spherical shapes were observed as seen in Figure (6a). The agglomerates
Vol.9, No.8 Synthesis of Hydroxyapatite 689
(Fig: 6b and 6c) were of irregular shape like oval shape and spherical shape. Agglomerates as big
as 10µm could also be seen, however, the dominant sizes were between 3 and 5µm. There are
many spherical agglomerations and crystallites of nano-sized with a tendency to agglomerates
leaving pores in between. The formations of pores are beneficial as they would permit the
circulation of body fluid throughout the coating when it is used as biomaterial.
DTA-TG (Fig.5) analysis shows that there is weight loss of around 6% upto temperature 3800C
and 10% in the range 3800C to 4200C. This major loss confirmed the formation of HAp,
similarly about 9% wt. loss was observed upto 8000C.Beyond 8000C to 14000C no significant wt.
loss was observed. Almost stable curve was noticed within this temperature range, which
indicates thermal stability of HAp powder.
The result shows thermal stability of HAp beyond the temperature 10500C as proposed [17]. In
DTA curve there is indication of endothermic sharp peak at 4200C with two other small peaks.
Fig.5: DTA-TG analysis of synthesized HAp.
Temp Ce l140012001000800600400200
TG %
DTG m g / min
266.4 ug/min
95.4 ug/min
78.6 ug/ min
3.48 uV
5.12 uV
177 uJ/mg
21.7 uJ/m g
690 P. Hui, S.L. Meena, G. Singh, R.D. Agarawal, S. Prakash Vol.9, No.8
Fig. 6a & 6b: SEM micrographs of synthesized HAp
Fig.6c: SEM micrographs of synthesized HAp
6a 6b
Vol.9, No.8 Synthesis of Hydroxyapatite 691
HAp has been successfully synthesized by reaction of discarded hen eggshell with tri-calcium
phosphate in presence of steam at 900oC and subsequent aging for 24 Hrs results in formation of
synthesized HAp. As revealed by FT-IR and XRD analyses, the product is crystalline & DTA-
TG shows good thermal stability. The particles are mostly spherical with nano-size. This method
requires only low temperature treatment (9000C) as compared to conventional method where
temperature of treatment is 10500C.
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