β-TCP Phase Research Articles

Structure reinforcement of porous hydroxyapatite pellets using sodium carbonate as sintering aid: Microstructure, secondary phases and mechanical properties

Porous HAP pellets suitable for loading therapeutic agents were prepared using microcrystalline cellulose (MCC) as pore former and sodium carbonate as sintering aid (SAID). The effect of sintering temperature on the microstructure, mechanical properties and disintegration of pellets prepared at different SAID content was studied. Pellets were characterized by SEM, image analysis, porosimetry and surface area. Secondary phases were identified by PXRD, ATR-FTIR and Raman spectroscopy. Increasing the sintering temperature decreased the diameter, porosity, surface area and friability of the pellets but increased the pore size, tensile strength and disintegration time. The effect of SAID was dependent on sintering temperature. With 5% SAID, a secondary β-tricalcium phosphate (β-TCP) phase was formed, indicated by FTIR peak at 980 cm−1 and characteristic PXRD reflections, whereas with 10%, a secondary B-type carbonated hydroxyapatite phase (CHA) formed, indicated by FTIR peaks at 878 and 1450 cm−1, a broad Raman peak in the region 1020 to 1050 cm−1 and PXRD reflections. Pellets prepared with SAID showed high strength and also porosity. The biphasic HAP/β-TCP pellets exhibited remarkably great strength (4.39 MPa) at the high sintering temperature, while still retaining 43.9% porosity. Relationships were established between the mechanical properties or disintegration time of the porous pellets and the microstructural parameters.

Effect of fluorine substitution on sintering behaviour, mechanical and bioactivity of hydroxyapatite

Fluorine substituted hydroxyapatite (FAp) with different degree of fluorine (F) substitution, has been synthesized using hydrothermal synthesis method. In the present work, as synthesized powders were consolidated by sintering at 1200 °C in air for 1 h. The sintered specimens were characterized using Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) for phase analysis. Further, fluorine intake in the sintered specimens was evaluated using ion chromatography (IC). XRD peaks clearly showed biphasic nature of the sintered specimen. However, the sintered samples containing more than ∼60% fluorine substitution showed no β-tricalcium phosphate (β-TCP) phase formation. The IC results revealed that the degree of fluoridation decreased significantly in the sintered specimen compare to the respective as synthesized powders. The effect of actual fluorine content in the sintered specimens was further evaluated in terms of sinterability, surface energy, mechanical properties and in vitro cytocompatibility study. The surface energy of the sintered specimen decreased from 51.8 mN/m to 42.5 mN/m, in which degree of fluoridation varies from 0% to 110%. The in vitro cytocompatibility of the sintered specimen were carried out against mouse osteoblast cell line (MC3T3-E1). In vitro study showed that all the samples were nontoxic but cell proliferation for the samples containing more than 40% fluorine substitution became significantly low.

Assessment of phase stability and in vitro biological properties of hydroxyapatite coatings composed of hexagonal rods

We describe fabrication of hydroxyapatite coatings consisting of micrometric hexagonal crystals on titanium substrate. The aim was to evaluate their phase stability and in vitro performance. We employed a facile hydrothermal method assisted with a chelating agent and monoethanolamine as regulators of the nucleation and crystal growth. After the hydrothermal reaction, the hydroxyapatite coatings were sintered at different temperatures up to 950 °C. We performed in-depth investigations into the coating surface morphology, topography, wettability, and chemical composition using scanning electron microscopy, profilometry, sessile drop technique, x-ray diffraction and Raman spectroscopy. We assessed the bioactivity of hydroxyapatite structure sintered at different temperatures after incubation in the SBF solution. Simultaneously, we conducted a series of in vitro experiments based on MTT assay using MC3T3 mouse preosteoblast cell line to study the cytocompatibility of synthesized specimens. The results show that the thermal processing of hydroxyapatite coatings leads to their thermal decomposition to β-TCP phase already at 700 °C. As the heat treatment progresses, the edges of hexagonal crystals are melting and smoothing. We show that while as-prepared hydroxyapatite coating exhibits remarkable bioactivity after just 3 days, the sintered samples are not bioactive at all. Biological examination with MC3T3 cells indicates good compatibility of all coatings, with cell proliferation being enhanced on samples heated at higher temperatures. In conclusion, the heat treated HAp coatings with different morphologies and different HAp/β-TCP phase ratios influence the in vitro bioactivity and response of preosteoblast cells.

Microstructural, mechanical and biological properties of hydroxyapatite - CaZrO3 biocomposites

The biofunctionalization of metal implants with bioactive ceramics arises as an appealing strategy for promoting their osseointegration, without impairing implants’ good mechanical resistance. In this work, biocomposites of hydroxyapatite - CaZrO3 were obtained by rate controlled sintering and their microstructure, mechanical properties, biological as well as the effect of stoichiometric calcium zirconate dopant on the decomposition of HA were analysed. The results obtained showed that the addition of CaZrO3 stabilizes the hydroxyapatite at least up to 1300 °C and inhibits the appearance of the α- and β-TCP phases. Moreover, the mechanical properties of the hydroxyapatite were improved with 10 wt% of CaZrO3, despite the increase of porosity. The in vitro assays demonstrated that the biocomposites were biocompatible, since they favoured human osteoblast cells adhesion and proliferation. All the data obtained emphasize the potential of these biocomposites for the aimed biomedical application.

Evaluation of crystalline indexes obtained through infrared spectroscopy and x-ray diffraction in thermally treated human tooth samples

The crystalline indexes obtained through infrared spectroscopy (CIIR) and X-ray diffraction (CIXRD) were used to analyze the structural changes of dentin and enamel in human teeth when subjected to heat treatments between room temperature (25 °C) to 1200 °C in atmospheric air and argon. Thermogravimetric (TGA) and differential scanning calorimetry (DSC) analyses of sound powders were also used to support the analysis. As the temperature increased, the CIXRD increased exhibiting a behavior like that of the crystal grain size, and the CIIR increased until the β-TCP phase appeared. These results indicated that the CIIR was more variable to structural changes than the CIXRD.

Crystallization behavior of low-cost biphasic hydroxyapatite/β-tricalcium phosphate ceramic at high sintering temperatures derived from high potential calcium waste sources

Abstract This paper reported the formation of biphasic hydroxyapatite, (HA) and β-tricalcium phosphate, (β-TCP) sintered at various sintering temperature from waste material. The phase stability of HA ceramic was investigated by imposing the high sintering temperature in order to study the transformation of the single phase of HA to biphasic HA/β-TCP ceramic. The evolution microstructure of HA and biphasic HA/β-TCP ceramic was studied at various sintering temperature reach up to 1400 °C. The single phase of HA was observed from 200 to 1200 °C and the secondary phase β-TCP appears due to the decomposition of partial HA at 1300–1400 °C. The optimum temperature for a single phase of HA was identified after sintering at 1200 °C to produce HA with high mechanical hardness about 5.11 GPa. This is clearly related to the phase stability and morphology of HA. The particles size of HA as-synthesized were recorded in nano range scale at ∼9 to 20 nm. However, the average particle sizes become larger and compact between ∼0.21 and ∼3.3 μm from 600 to 1200 °C. Thus, the sintering temperature gives an impact on the phase stability, microstructure and microhardness of HA derived from high potential waste sources.

Strontium doped hydroxyapatite from Mercenaria clam shells: Synthesis, mechanical and bioactivity study

Synthesis of strontium-doped hydroxyapatite from Mercenaria clam shells has been carried out by hydrothermal method. The doping of bioceramic, processed from biogenic resources is mostly unexplored. The objective is to understand the effect of strontium (Sr) incorporation on phase stability, sintering behaviour, mechanical properties and cytotoxicity of hydroxyapatite (HAp) derived from clam shells. The different molar concentrations of Sr, varies from 10, 30, 50, 70% of Ca, were substituted into the HAp. The synthesized powders were sintered at 1200 °C in air. The as synthesized powders and sintered specimens were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and high resolution transmission electron microscopy. The crystallite size and cell parameters of sintered specimens were analyzed from XRD. The XRD of hydrothermally synthesized powders mostly matched with HAp with slight shifting due to Sr doping. However, some distinct Sr based compounds were also observed where Sr substitution is more that 50% of Ca. The XRD of sintered specimen showed increasing β-tricalcium phosphate (β-TCP) phase with Sr substitution. The sintered density of solid samples gradually increased from 3.04 g/cc to 3.50 g/cc and surface energy decreased with increasing Sr substitution. Similarly, microhardness, fracture toughness and nanohardness of solid samples found to be enhanced with Sr substitution. The elastic modulus gradually increased from 130 to 137 GPa for HAp and Sr substituted HAp (70% of Ca). The in vitro cytotoxicity of sintered specimen against mouse osteoblast cell line showed that all the samples were nontoxic. However cell proliferation found low for the solid samples containing more than 50% Sr substitution.

Structural, dielectric, cytocompatibility, and in vitro bioactivity studies of yttrium and strontium co-substituted nano-hydroxyapatite by sol–gel method

Synthetic nano-biomaterials with inclusion of dual minerals can stimulate bone bonding ability and their preferable non-cytotoxicity makes them applicable for orthopedic and dental implants. The present work deals with the effect of doping Y3+ alone and Y3+/Sr2+ on HA nanoparticles by sol–gel technique. The synthesized samples were characterized by XRD, FT-IR, FE-SEM, TEM, and EDAX to check the crystallite size, crystallinity, structure, and phase composition. The dielectric and electrical properties were also studied at room temperature. The prepared samples consisted of a well-crystalline pattern admixture with a minor phase of β-TCP. Investigations reveal that the amount of Y3+dopant caused no significant distortion in the crystal structure of HA, but decreased the crystallinity and crystallite size considerably. The absorption bands related to the hydroxyl and phosphate groups observed in FT-IR spectra confirmed the formation of HA structure. The increase in ac conductivity (σac) with increasing applied frequency confirmed that all samples follow the universal power law. Moreover, in vitro apatite-forming ability of Y3+/Sr2+ co-substituted HA nanoparticles was investigated by immersing in the simulated body fluid (SBF) for 7, 14, and 21 days. The samples did not show any harmful distress on the growth of A549 cells, which confirmed that they are potential candidates for biomedical and material science engineering.

Calcium phosphates of biological importance based coatings deposited on Ti-15Mo alloy modified by laser beam irradiation for dental and orthopedic applications

Ti-15Mo alloy samples were irradiated by pulsed Yb:YAG pulsed laser beam under air and atmospheric pressure. Sequentially, calcium phosphate coatings were deposited on the irradiated surfaces by the biomimetic method. The formation of calcium phosphates (CaP) under biological medium and SBF (Synthetic/Simulated Body Fluid) occurs in the presence of Ca2+ and PO43- ions, as well as ions such as: Mg2+, HCO3-, K+ and Na+, which facilitates the mimicking of the biological process. The biomimetic calcium phosphates-based surfaces were submitted to heat treatment conditions at 350 °C and 600 °C. The present study correlates four conditions of fluency (1.91, 3.17, 4.16 and 5.54 J/cm2, respectively) as established have a sufficient energy to promote ablation on the laser beam irradiated surfaces. Likewise, it has been demonstrated the processes of fusion and fast solidification from the laser beam irradiation, under ambient atmosphere, inducing the formation of stoichiometric (TiO2) and non-stoichiometric titanium oxides (TiO, Ti3O, Ti3O5 and Ti6O) with different oxide percentages depending on the fluency applied. Besides that, laser modification has allowed a clean and reproducible process, providing no traces of contamination, an important feature for clinical applications. The morphological and physico-chemical analysis indicated the formation of a multiphase coatings depending on the heat treatment temperature performed to 350 °C (ACP1–2, CDHA, HA phases) and 600 °C (CDHA, HA and β-TCP phases). It is worth noting multiphasic bioceramic systems has been gaining attention for biomedical applications. The laser beam irradiation associated to bioactive coatings of calcium phosphates of biological interest have shown to be promising and economically feasible for use in clinical applications.

XRD Analysis of Calcined Magnesium Substituted Biphasic Calcium Phosphate (Mg-BCP)

The incorporation of magnesium (Mg) in biphasic calcium phosphate (BCP) was prepared through precipitation method. The concentration of added Mg was varied with respect to calcium (Ca) precursor molarity as such Mg/Ca molar ratio were 0.05 and 0.1, while the (Ca + Mg)/P ratio was maintained at 1.59 throughout the experiment to ensure that calcium deficient apatite was formed. Precipitate obtained was aged for 24 h in ambient condition followed by decantation, centrifugation and drying at 90°C overnight. The as-synthesized powders were calcined at 600°C and characterized by X-ray diffraction (XRD) via Rietveld refinement (X’Pert HighScore Plus software). Both as-synthesized and calcined Mg-BCP powder contains hydroxyapatite (HA) and beta-tricalcium phosphate (β-TCP) phase with Mg in its lattice. The substitution of Mg in calcium-deficient apatite resulted in the formation of biphasic mixtures of β-TCP/HA after calcinations with shifted peaks β-TCP when compared to reference β-TCP peaks. High deficiency of calcium in apatite enables more substitution of magnesium thus stabilizing β-TCP phase when subjected to high temperature.

Femtosecond laser impact on calcium phosphate bioceramics assessed by micro-Raman spectroscopy and osteoblastic behaviour

The present work is an investigation of the biological response to the presence of grooves 3 μm deep, 15 μm wide and spaced by 100 μm, produced with femtosecond laser on β-tricalcium phosphate (β-TCP). The heat affected zone generated by the laser irradiation was investigated. Micro-Raman spectroscopy showed a transformation from β-TCP phase into α-TCP phase, localised inside the grooves. The X Ray Diffraction analyses, correlated with micro-Raman data, confirmed that the use of femtosecond pulsed laser enables to limit the thermal impact. A selection of optimised process parameters allowed to obtain β-TCP micro-patterned surfaces avoiding any phase transformation. The increase of the wettability with the micro-patterning, compared to smooth surfaces, was highlighted. An improvement of the osteoblastic proliferation was also demonstrated. Finally, the tendency of cell elongation along the grooves direction showed the ability of osteoblastic cells to adapt their morphology to the support topography on which they grow.

Multi-element substituted hydroxyapatites: synthesis, structural characteristics and evaluation of their bioactivity, cell viability, and antibacterial activity

Synthesis of unsubstituted and multi-element (magnesium, zinc and cobalt) substituted hydroxyapatites (HAP) with varying stoichiometric compositions and evaluation of their morphological and structural characteristics, degree of crystallinity, bioactivity, cytotoxicity and antibacterial activity are addressed. The morphological features are not altered much following the substitution of Mg2+, Zn2+, and Co2+ in the HAP lattice. Nevertheless, their substitution exerts a strong influence on the structural characteristics HAP. Rietveld refinement analysis of the X-ray diffraction patterns indicates a decrease in crystallinity and mineralogical composition of HAP phase, which is accompanied with an increase of β-tricalcium phosphate (β-TCP) phase along with Co3O4 phase. Broadening of the PO43− peaks and a decrease in intensity of the OH− peak are observed by Fourier-transform infrared spectra. A decrease in intensity, broadening and a slight shift in Raman band (at 961 cm−1 for HAP) towards the lower side suggest the incorporation of Mg, Zn, and Co, disordering of the crystal structure of HAP and formation of β-TCP as additional phase besides HAP. The MgZnCo-HAP’s exhibits a better bioactivity, cell viability and anti-bacterial activity than the unsubstituted HAP. However, a decrease in cell viability and anti-bacterial activity are observed when the stoichiometric ratio of the substituent elements is relatively higher.

Biomimetic calcium phosphates-based coatings deposited on binary Ti-Mo alloys modified by laser beam irradiation for biomaterial/clinical applications

ABSTRACTBiomimetic Method has been widely used to prepare calcium phosphate coatings on Ti and its alloys. This modification is based on a Synthetic/simulated Body Fluid (BSF) which facilitates the mimicking of the biological process in order to provide hard tissue repairs. The formation of HA and other calcium phosphates under biological medium and SBF occurs in the presence of Ca2+ and PO43- ions, as well as essential ions such as: Mg2+, HCO3-, K+ and Na+. Ti-15Mo alloy samples were irradiated by pulsed Yb: YAG pulsed laser beam under air and atmospheric pressure. Sequentially, calcium phosphate coatings were deposited on the irradiated surfaces by the biomimetic method. The biomimetic calcium phosphates-based surfaces were submitted to heat treatment conditions at 350°C and 600°C. The present study correlates two conditions of fluency (1,91 and 5,54 J.cm-2) as established have a sufficient energy to promote ablation on the laser beam irradiated surfaces. Likewise, it has been demonstrated the processes of fusion and fast solidification from the laser beam irradiation, under ambient atmosphere, inducing the formation of stoichiometric TiO2 and non-stoichiometric titanium oxides, including Ti3O5, TiO, Ti3O and Ti6O with different oxide percentages depending on the fluency applied. Besides that, laser modification has allowed a clean and reproducible process, providing no traces of contamination, an important feature for clinical applications. The physico-chemical and morphological analysis indicated the formation of a multiphase coatings depending on the heat treatment temperature performed to 350 °C (ACP1 and 2, HAD, HA phases) and 600 °C (HAD, HA and β-TCP phases). It is worth noting that multiphasic bioceramic systems has been gaining attention for biomedical applications. Thus, the laser beam irradiation associated to bioactive coatings of calcium phosphates of biological interest have shown to be promising and economically feasible for use in dental and orthopedic implants.

Structural Changes in Human Teeth after Heating up to 1200°C in Argon Atmosphere

The phase transformation of hydroxyapatite (HAP, Ca10(PO4)6(OH)2) to the beta tricalcium phosphate phase (β-TCP, β-Ca3(PO4)2) at 1100°C is well known. However, in the case of human tooth, the HAP phase transformation is still an open area. For example, the CaO phase has sometimes been reported in the set of phases that make up the teeth. In this study, physical changes of human teeth when subjected to heat treatment in inert atmosphere (argon) were studied. The results were compared with those obtained in air atmosphere, from room temperature (25°C) up to 1200°C. Morphological changes were analyzed by light and scanning electron microscopy (SEM). The HAP to β-TCP phase transformation was followed in powder samples by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Heating of teeth results in the removal of organic material and structural water before the HAP to β-TCP phase transformation, the increment in hardness and the induced crystal growth. The percentage of the phases, crystal growth and lattice parameter variations as a function of temperature was quantified by Rietveld analysis. The black color was observed in dentin heated under argon atmosphere. Differences in expansivity produce fractures in dentin at 300°C in argon and at 400°C in air. In dentin, the coexistence of the HAP and β-TCP phases was observed after 800°C in argon and after 600°C in air; in enamel it was observed at 600°C in argon compared with 400°C in air. In general, the role played by the argon atmosphere during the thermal treatment of the teeth is to retard the processes observed in air.

Study on the Structure and Properties of Crystalline Pure and Doped β-Tri Calcium Phosphate Ceramics

Resorbable Calcium Phosphate based bio-ceramics find wide application in arthroplasty. It requires better in-vivo mechanical strength and stability to effectively exploit the resorption behaviour. Present study reports synthesis and thorough characterization of undoped β-TCP along with Magnesium and Titanium doped (3wt% and 5 wt.%) β-TCP. Density, porosity, grain size and shape, percentage shrinkage and particle size distribution were measured. XRD and FTIR were done to examine the changes in crystalline phases and functional groups of all these ceramics. Scanning electron microscopy (SEM) was used to study the interconnectivity of pores, pore shape and size. Finally hemolysis study was done to understand the degree of hemocompatibility. Primary results suggest that all the samples retained β-TCP phase, structures were submicron grained with uniform, nodular grains and good amount of porosity. All specimens revealed high hemocomptaibility.

Characterization of Hydroxyapatite (HA) Sputtering Targets by APS Methods

Radio frequency (RF) sputtering is a potential medical device coating technology that is commercializable; however, a suitable commercialized target for sputtering the hydroxyapatite (HA) coating onto titanium medical devices is more important. Therefore, this study used three HA targets in conducting sputtering experiments for HA films, which were manufactured in a laboratory by using three different processes: cold pressing and sintering (CPS), hot isostatic pressing (HIP), and atmospheric plasma spraying (APS). Subsequently, the sputtering performance of each type of target and the properties of the HA films were assessed to develop an appropriate process for modifying the surfaces of medical devices. The experimental results showed that the APS target, with a density of approximately 2.83 g/cm3, was suitable for use in HA sputtering. Additionally, the APS target could withstand a high discharge power over 300 W, whereas the CPS target could nearly endure a power below 70 W. The APS target, with Ca/P ratio of 2.401, consisted of a combination of HA, α-tricalcium phosphate (α-TCP), β-TCP, and tetracalcium phosphate phases (TTCP). In addition to being able to perform at a high sputtering power of more than 300 W, the APS target achieved a higher deposition rate than did the CPS target. This study shows that the processing technology used for the APS target is a potential method for applying HA sputtering for the surface modification of artificial aggregates.

Wet chemistry approach to the preparation of tantalum-doped hydroxyapatite: Dopant content effects

Tantalum-doped hydroxyapatite (Ta-doped HA) nanopowders with different Ta contents were synthesized by a wet-chemical precipitation route. The structure modification and charge compensation mechanism were investigated by various characterization techniques. Due to the smaller size of tantalum ions compared to the Ca2+ size, it was assumed that the tantalum ions occupy either the Ca2+ and/or the interstitial positions in the HA lattice, where the charge imbalance from to this substitution was compensated by the Ca2+ vacancies. From the XRD patterns, the as-synthesized nanopowders were poorly crystalline apatite in the absence and presence of different dopant contents. The hexagonal HA and tricalcium phosphate (β-TCP) phases as biphasic calcium phosphate mixtures were formed after heating at 900°C. In addition to the β-TCP phase, minor extra phases such as calcium oxide (CaO) and calcium pyrophosphate (Ca2P2O7) were identified from the HA decomposition. The FTIR results indicated that the decrease of structural hydroxyl groups depended on both tantalum oxyanions and carbonate contents. In the XPS profile, the Ta 4f peak of the doped sample could be decomposed into four main components, which showed different oxidation states for tantalum (TaO2 oxide). According to the TEM observations, the doped calcined powder at 900°C was composed of uniform nanoneedles with an average length and width of 120 ± 50 and 10 ± 5nm, respectively.

Effect of Pressure and Temperature in Solid State Sintering Approach Producing Porous Tricalcium Phosphate Bioceramics

Porous Tricalcium Phosphate (TCP) is recognized as a good biomaterial having excellent biocompatibility, biodegrability and bioresorbability. Some of the techniques to produce porous β-TCP, are replica technique (polymeric sponge method), sacrificial template method and direct forming method, however, these methods are complicated and can be costly. In this study, solid state sintering was adopted to form porous TCP as a new approach to overcome these problems. TCP bioceramic was prepared by mixing calcium hydrogen phosphate dihydrate and calcium carbonate. The powders were pressed into pellet form with four different pressures; 10, 20, 30 and 40 MPa. Then, the pellets were sintered at 1100°C to 1400°C and subsequently characterized by X-ray diffraction (XRD), density and porosity measurement, diametral tensile strength test (DTS) and scanning electron microscopy (SEM) evaluation. β-TCP phase was maintained at 1100°C and 1200°C whilst α-TCP phase had formed as second phase above 1300°C. The highest apparent porosity (60.93%) was obtained at 10 MPa and 1100°C sintering temperature, with the density of 1.12 g/cm3. The DTS values were in the range of 0.31 to 3.78 MPa in with lower DTS values were obtained at low compaction pressure and sintering temperature. Interconnected pores with high level porosity were observed at the fracture surfaces of the sintered pellets. Intraporosity was also observed. In conclusion, TCP bioceramics with interconnected pores were produced via solid state reaction; however, more work is required to improve the level of porosity.

Effect of Calcination Temperatures on Phase Transformation and Stability of β-Tricalcium Phosphate Powder Synthesized by a Wet Precipitation Method

Beta-tricalcium phosphate (β-TCP) was never synthesized directly using an aqueous method. As-precipitated powder from a wet chemical method needs to undergo a heat-treatment process (or calcination) to enable the intermediate phase (s) to be transformed into single-phase TCP. In this work, calcium hydroxide, (Ca (OH)2), and phosphoric acid, (H3PO4), were mixed as the precursor materials with a Ca/P ratio of 1.5,. The mixture was stirred at a fixed stirring speed of 200 rpm and a stirring duration of 2 hours. The precipitate thus obtained was filtered and dried overnight before being tested by differential scanning calorimetry and thermogravimetry (DSC/TG) up to 1300°C for thermal behaviour upon firing. The powders were then calcined at various temperatures (500°C, 700°C, 900°C 1000°C, 1100°C, 1200°C and 1300°C) for a duration of 2 hours. The calcined powders obtained were analysed by x-ray diffraction (XRD) to determine the transformation of phases. Monetite and hydroxyapatite were the phases detected after calcination at 500°C and 700°C, whilst at a temperature of 900°C up to 1300°C, only a single phase β-TCP was observed. Microstructural observation by scanning electron microscopy (SEM) was conducted on the β-TCP powders obtained at calcination temperatures of 900°C to 1300°C. The results showed a massive crystal growth of the aggregated particles, but even so, the phase remained stable as monolithic β-TCP.

Synthesis, structure refinement and vibrational spectroscopy of new rare-earth tricalcium phosphates Ca9RE(PO4)7 (RE = La, Pr, Nd, Eu, Gd, Dy, Tm, Yb)

Abstract Rare earth elements – doped β-tricalcium phosphates Ca 9 RE (PO 4 ) 7 ( RE = La, Pr, Nd, Eu, Gd, Dy, Tm, Yb) were synthesized by solid-state reaction at T = 1200 °C. The obtained RE -doped β-TCP phases were studied by a combination of Scanning Electron Microscopy (SEM) equipped with energy dispersive X-Ray spectroscopy (EDS), X-ray diffraction (XRD), Fourier Transform Infra Red (FTIR) and Raman spectroscopies. SEM morphological analyses revealed the presence of sub spherical micro crystalline aggregates, while EDS semi-quantitative analyses confirmed the nominal RE /Ca composition for all the phases. The unit cell and the space group were determined by X-ray powder diffraction data showing that all phases in the series crystallize in the rhombohedral R 3 c whitlockite-type structure; the unit cell constants are a linear function of the dimension of the substituting rare-earth element, and range from a = b = 10.4695(3) A, c = 37.500(3) A and V = 3559.7(2) A 3 (La) up to a = b = 10.4073(2) A, c = 37.2725(2) A, V = 3496.2(2) A 3 (Yb). The analysis of each compound was completed with the structure model refinement by the Rietveld method and the distribution of RE within the available structural sites is discussed according to the results of the Rietveld refinement. The FTIR and Raman spectra show slight band shifts of the phosphate modes correlated to the evolving size of the RE element.