Preparation and Characterization of Hydroxyapatite by the precipitation method and heat treatment

Hydroxyapatite is a synthetic substance in the form of microspheres composed of calcium and phosphate, present in human bones and tooth enamel. The objective of the work was to synthesize hydroxyapatite, from the solution of calcium nitrate and diamonic phosphate by the method of precipitation and heat treatment, obtaining the hydroxyapatite in powder form. To study its structural evolution, Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and Raman spectroscopy were used. The results show that the hydroxyapatite nanocrystalline can be successfully produced by the precipitation technique from raw materials.


Introduction
The biomaterials have been getting one large attention by part of the scientific community. The hydroxyapatite (HAp), with its chemical formula of (Ca5(PO4)3OH, and ratio of Ca/P equal to 1.67 (Santos, 2005). Is a bioceramic widely studied due to their chemical similarity to component mineral from bone. in addition, it is biocompatible, non exhibits effects cytotoxic, bioactive and thermodynamically stable in the fluid body, as well as with hard tissue, skin and muscle, which places as an attractive material for a wide range of applications in the field biomedical. Unfortunately, due to low stability, especially in environments wet, the HAp currently not can be used to load heavy applications, such as teeth or artificial bones (Suchanek, Yoshimura & Mater, 1998).
Various techniques have been used for the preparation of HAp powders. Two most used ways are wet methods and solid state reactions. The first method can be divided into three groups: precipitation, hydrothermal technique and hydrolysis of other calcium phosphates (Aoki, 1991).
It is possible to improve the properties of HAp ceramics, controlling important parameters of precursors in their preparation reaction, such as particle size and shape, particle distribution and agglomeration (Best & Bonfield, 1994). After nanocrystalline of HAp exhibit greater surface area (LeGeros. (1993). It can provide better density and reduced sintering temperature (Yeong, Wang & Ng, 1999). In addition, it is also expected that HAp when in nanometric character has better bioactivity than larger crystals (Stupp & Ciegler, 1992) . Recently, the use of precipitation processes for the synthesis of HAp has become an important research objective ( Han, et al. 2004). The HAp pure crystallizes in the monoclinic form at temperatures up to 250 ° C; however, above this temperature, the phase transition to the hexagonal form occurs with space group P 63/m. Natural HAp crystals exhibit hexagonal conformation and have a single cell with network parameters: a = b = 9.389 Å and c = 6.869 Å, α = β = 90 and γ = 120 (Brundavanam et al., 2013). Development, v. 9, n. 6, e172963549, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i6.3549 4 The objective of the work was to synthesize hydroxyapatite, from the solution of calcium nitrate and diamonic phosphate by the method of precipitation and heat treatment, obtaining the hydroxyapatite in powder form.

Methodology
The sample was prepared through the synthesis of nanocrystalline hydroxyapatite using the precipitation method, by the author Mobashenpour et al (2007). This method uses the hydrated calcium phosphate solution of hydrated calcium nitrate and diamonium by the method of precipitation and heat treatment of hydroxyapatite powders.
Such a technique involves wet reactions between calcium and phosphorus precursors with temperature and pH control of the solution. The precipitated powder is calcined at 400-600°C or even at higher temperatures, in order to obtain a stoichiometric apatite structure. Rapid precipitation during the titration of the phosphate solution in calcium solution can lead to a lack of chemical homogeneity in the final product. Slow titration and diluted solutions should be used to improve the chemical and stoichiometric homogeneity of the resulting HAP.
Careful control of the solution conditions is critical in wet precipitation. The identification of the sample synthesized by X-ray diffraction was carried out on a Panalytical diffractometer, in which experimental set up detections of 40 kV, current of 30 mA and observation range between 30º ≤ 2θ ≤ 90º were used. The X-ray diffraction analysis was carried out in the design department of the Federal University of Pernambuco, campus agreste. The commercial software Origin was used, based on simulated X-ray diffraction data, to model the crystalline structure of the HAp powder . Research, Society and Development, v. 9, n. 6, e172963549, 2020 (CC BY 4. The Scherrer equation is one of the most used ways of calculating particle size using X-ray diffraction data. This method takes into account the fact that the widening of the diffraction peak is caused by the size of the crystallite. A single unit cell of HAp consists of 44 atoms, with 10 atoms of calcium (Ca), 6 atoms of phosphatotetrahedral (PO 4 3-), and 2 OH groups very well organized in the hexagonal atomic structure (Brundavanam et al, 2013). The network parameters of HAp , obtained from X-ray diffraction measurements, are a = b = 9.389 Å and c = 6.869 Å. The hexagonal cell of the space group P63 / m has a cell volume of 528.79 Å3 (Tas, 2001).  In comparison with the sample of HAp sintered by precipitation, we could see peaks similar to those of the author Lopes et al. (2015), also in the 002, 211 and 300 plans, the values were not closer due to the difference in crystallinity of the HAp samples. Figure 2 shows the spectrum obtained from the sample, where its peaks are narrower compared to figure 1, thus characterizing the sample obtained as more crystalline.  In the synthesized sample, the main peaks present in hydroxyapatite were identified, especially those obtained at points 400, 600 and in the range 900 to 1000. When comparing in the literature a Raman spectrum obtained from a hydroxyapatite of a dental enamel by studies of Torres-Gallegos et al. (2012) it was possible to identify a similar profile. as well as the signals 600 and 950. As well the requirement main scan as a positive identifier for identifying hydroxyapatite obtained using this analysis tool. Development, v. 9, n. 6, e172963549, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i6.3549 8 Small displacements are also observed in the bands corresponding to OH -. The difference between treated samples at temperatures below 900°C and treated at temperatures higher than those, present only in the samples treated below 900°C (bands at 1458 cm -1 and 1413 cm -1 ) should be noted , what with chance is the least crystalline. The presence of this ion, occluded within the structure and not as a phase, shows how it competes with OH and phosphates. In addition, at low calcination temperatures, its presence may be due to an inconclusive reaction, given the short time that the system has to achieve its stability.

Final Considerations
It can be concluded that the hydroxyapatite compound with nanoparticles can be successfully produced by the precipitation technique from Ca(NO3)2 · 4H2O and solution (NH4)2HPO4 as starting materials.
The powder consists of fine particles, forming uniform and dispersed agglomerates.
Clinical cases have shown that this product is effective for causing bone tissue growth.