Hydroxyapatite (HA) having chemical formula Ca10(PO 4) 6(OH) 2, is the main chemical component of human bone tissue (70%). This is the reason why it has been widely engaged in the dental and non-load bearing implantations, to cope up with the bone response as a bioactive material. In this study HA powder was synthesized by wet chemical method, using phosphoric acid (H3PO4) and eggshells. The synthesized HA powder was characterized by X-ray diffraction analysis, Scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDX) and Fourier transform (FT-IR) spectroscopy. The Thermos gravimetric analysis (TGA-DTA) was also carried out to evaluate the stability of the synthesized HA powder at higher temperatures. The results of the study indicate that sintered (at 900°C) HA powder resembles the feature of pure and single apatite phase having favourable Ca/P ratio ranging from 1.7 to 2.4.
Hydroxyapatite (HA) is the most resourceful inorganic biomaterial used for biomedical application [
Human bone contains of 70% apatite calcium phosphate and 30% other organic elements (largely collagen). This 70% calcium phosphate resembles the crystal structure as HA [
Many researchers have tried to synthesize the HA through various routes. Some of the conventional routes of producing HA include wet precipitation method, hydrothermal technique, low temperature synthesis, solid state reaction and sol-gel technique [
A huge amount of eggshells is left daily, which are of no use and produce waste. These eggshells support microbial action and lead to pollute environment. Annually around 250,000 tons of eggshell are only produced annually by food processing industry. Eggshell corresponds to 11% of the total weight of an egg. These eggshells mainly contain calcium carbonate (91% - 94%), calcium phosphate (1%) and other organic matters, which makes it preferable for synthesizing CaO [
The experimental procedure is divided into three parts which deals with preparation of CaO from egg shell, synthesis of HA powder from CaO and phosphoric acid, and characterization of HA powder.
The major constituent exists in the eggshell is CaCO3, which accounts nearby 94% of the overall weight. Thus, in this method hen’s eggshells were used to synthesis CaO. The uncrushed eggshells were taken in bulk and cleaned by hand with deionized water. It was then boiled in water for about half an hour in an oven, showing in
Further the cleaned eggshells were kept in a porcelain vessel and were calcined in a tube furnace at 900˚C for one hour, showing in
A measured amount of calcined eggshell power was taken in a beaker and dispersed in distilled water. This stoichiometry amount was decided in accordance with the quantity of calcium present in the calcined eggshell. In this reaction the CaO transforms into Ca(OH)2 as shown in below equation [
The reagent grade 0.6M solution of orthophosporic acid was added to the Ca(OH)2 solution. The drop wise solution was added at a precise rate, to decrease the pH of the solution up to 8.5. The precipitation formation was observed at this point. Further, the solution was kept for 24 hours at ambient temperature, which cause the
precipitation hardening. The solution was further stirred for another 30 minute on a magnetic stirrer and then left over for another 24 hour, which helps to complete the formation of precipitation. The expected reaction for this process is as follows [
The precipitate was filtered with filter paper and washed carefully with double distilled water and again filtered using filter paper. The precipitation was again kept in the oven for 2 hours at 100˚C for drying. The dried precipitation was further calcined at 900˚C for 2 hours in the tube furnace as
The morphological characterization of the HA powder was conducted using the field emission scanning electron microscope (Quanta 200; FE-SEM). The phase composition of HA powder was determined using X-Ray Diffraction Analysis (Bruker D-8 Advanced; XRD, Germany), which uses 40 kV voltage, 30 mA electron probe current and Cu target. Thermal stability and weight loss of the HA was estimated using thermo gravimetric analysis data (Perkin Elmer Elan DRC 6000; TG-DTA). The 10˚C/min heating rate was applied in air atmosphere, up to the 1400˚C temperature. The Fourier Transform-Infrared Spectroscopy (Thermo NICOLET 5700; FTIR) technique is used to identify the organic and inorganic functional group present in the HA powder. FTIR transmittance spectra of the HA powder samples were reported in the 4000 - 400 cm?1 region by using KBr pellet technique. The technique measures the absorption of infrared radiation by the sample material versus wave number. The infrared absorption bands identify molecular components and structures. The elemental analysis of the HA was conducted by the same FE-SEM instrument equipped with energy dispersive X-ray spectroscopy (EDX) system. All of the facility was used at the Institute Instrumentation Centre, IIT Roorkee.
The chemical reaction of CaO in Ortho phosphoric acid solution produces a white colour solid material. The material is having porous construction of the grains of irregular diameter. The X-ray diffraction of the sample is shown in
Determination of Particle Size
Determination of particle size was done by using the Debye-Scherrer formula represented by Equation (4). The particle sizes calculated for the corresponding peaks are represented in
synthesized HA powder is around 31.5 nm.
Diffraction angle in degree (2θ) | B (FWHM) in (˚) | b in radian (10−3) | Particle size D = (0.9*λ)/b cosθ (nm) |
---|---|---|---|
25.369 | 0.2429 | 4.237 | 35 |
31.376 | 0.367 | 6.402 | 23 |
39.372 | 0.333 | 5.809 | 26 |
46.259 | 0.341 | 5.948 | 26 |
49.102 | 0.306 | 5.338 | 30 |
63.793 | 0.199 | 3.482 | 49 |
Average Particle Size = (35 + 23 + 26 + 26 + 30 + 49)/6 = 31.5 nm.
Here λ = 0.154 nm for copper kα, and b = FWHM (full wave half maximum width), and θ = Diffraction angle (Here for FWHM the machine factor is 0.1).
The elemental analysis of the chemically produced HA powder is shown in
The SEM images of synthesized hydroxyapatite powder are shown in
The thermos gravimetric analysis was used for evaluating the thermal stability and weight loss of the HA samples. The heating rate of 10˚C/min was employed up to 1400˚C temperature in air atmosphere. It can be clearly observed from the DTA-TG analysis (show in
This research work presents a chemical method to produce pure, stoichiometry and stable HA powder using
eggshell and orthophosphoric acid. The XRD result reviles the crystallinity and the FTIR analysis evidences the phase purity of HA powder. From the EDX test of hydroxyapatite powder the ratio of Ca and P was found around 1.68. This is in an acceptable range, as in the ideal HA the weight ratio of Ca and P is 1.67. From the SEM analysis the prepared HA powder is found to be nanocrystalline nature. The TG-DTA analysis had been carried out and its results revealed thermal stability of the powder. The research shows the eggshell as a possible recycling material for producing HA powder, which can also help in waste management and keeping environment clean.
HimanshuKhandelwal,SatyaPrakash, (2016) Synthesis and Characterization of Hydroxyapatite Powder by Eggshell. Journal of Minerals and Materials Characterization and Engineering,04,119-126. doi: 10.4236/jmmce.2016.42011