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HA nanocomposite materials by hydrothermal synthesis
Journal of Alloys and Compounds 693 (2017) 221e225
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Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Preparation and characterization of BaTiO3/HA nanocomposite materials by hydrothermal synthesis Hua Jiao, Kang Zhao*, Lining Ma, Yufei Tang, Xiao Liu, Tierong Bian School of Materials Science and Engineering, Xi'an University of Technology, Xi'an, 710048, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 24 July 2016 Received in revised form 1 September 2016 Accepted 17 September 2016 Available online 19 September 2016
It was proposed that the piezoelectric effect played an important physiological role in bone growth, remodeling and fracture healing. Barium titanate/hydroxyapatite (BT/HA) nanorods piezoelectric composite was fabricated by hydrothermal process using 30 nm HA dissolved in different solvents (H2O, DMF, ethanol and ethylene glycol), and then reacted in the BaCl2, C6H8O7, butyl titanate mixture solution, respectively. The samples were characterized by XRD, IR, SEM and TEM to obtain sizes and crystal structure. The results showed that the BT/HA rod-like particles can be obtained at ethanol solvent, and the average diameter is about 30 nm and length is 150 nm. Meanwhile, BT/HA nanorod composites obtained at different solvents exhibited both good dielectric constant ε (18.45, 21.79, 27.40, 19.87), and piezoelectric coefficient d33 (2.74, 3.23, 6.88, 4.20), which were all higher than the piezoelectric coefficient of natural bone. The ε and d33 were improved by increasing the BT in ethanol solvent. © 2016 Elsevier B.V. All rights reserved.
Keywords: Nanorod composites Piezoelectric ceramics Hydroxyapatite/barium titanate Hydrothermal
1. Introduction Hydroxyapatite (HA) is chemically similar to the inorganic component of bone matrix with general formula Ca10(OH)2(PO4)6. HA particles on nanometric scale have been proved to be an osteo conductive material that also chemically binds to enamel and dentine [1]. HA is an attractive material for applications in the bone regeneration field due to its biological characteristics, such as being the major inorganic component of the bone matrix, its specific affinity toward many adhesive proteins, and its direct involvement in the bone cell differentiation and mineralization processes [2]. The close chemical similarity of HA to natural bone has led to extensive research efforts to use synthetic HA as a bone substitute and/or replacement in biomedical applications [3,4]. However, it shows poor biomechanical properties such as high brittleness, low fatigue strength and low flexibility [5]. Therefore, it is not suitable for direct-loading applications as well as application of dynamic force during the in vitro bone tissue engineering process. Due to the environment and biocompatibility concerns, many efforts were made to improve the bone healing response by using lead free piezoelectric ceramics, such as (Li0.06Na0.5K0.44)NbO3 (LNKN) [6], potassium sodium niobate (KNN) [7] and barium
* Corresponding author. E-mail address: [email protected] (K. Zhao). http://dx.doi.org/10.1016/j.jallcom.2016.09.175 0925-8388/© 2016 Elsevier B.V. All rights reserved.
titanate [8]. Barium titanate (BaTiO3, BT) is the most studied leadfree material used in the bone replacement and repair for more than 30 years. It exhibits excellent biocompatibility, and ability to form a strong interfacial strength with bone [8]. So far, all the piezoelectric ceramics used in vivo and vitro were in the dense bulk form. Recent advances in nanoscience and nanotechnology have reignited interest in the formation of nanosized HA and nanosized BaTiO3 using hydrothermal method [9e12], coprecipitation [13], sol-gel [14,15], sol - gel - hydrothermal method [16,17], template method [11,18] and molten salt method [19,20] to study of its properties on the nanoscale. Zhang et al. [8]. Has reported HA/ BaTiO3 piezoelectric composites which were fabricated by freeze casting hydroxyapatite/barium titanate (BT/HA) suspensions with the HA of 1 mm and BaTiO3 of 0.29 mm. The results of HA30/BT70 and HA10/BT90 composites exhibited piezoelectric coefficient d33 of 1.2 and 2.8 pC/N, respectively. To our best of knowledge, there is no report so far on the piezoelectric properties of nanosized BT/HA piezoelectric composites. In this study, BT/HA nanocomposites were obtained by a hydrothermal method. In order to provide the thorough information and find the most useful combination of the different properties used for the morphologies, piezoelectric and mechanical properties were investigated according to the processing parameters, i.e. BT/HA in different solvents.
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2. Experimental
free space (8.85 1012 F m1). A the area of the dielectric, t the thickness and ℇr is the dielectric constant of samples.
2.1. Materials Butyl titanate (C16H36O4Ti (Ti(OeBu)4)), (Tianjin Chemical Reagent Factory, China), and barium chloride dihydrate (BaCl2$2H2O) (Xi'an Chemical Reagent Factory, China)were used as the raw materials. Sodium hydroxide (NaOH) (Xi'an Reagent Factory, China) and citric acid (C6H8O7$H2O) (Tianjin Chemical Reagent Factory, China) was used as a mineralizer. HA powder with the median grain size d ¼ 30 nm and a purity of 99% (according to the manufacturer's data, Nanjing Emperor Nano Material Co., Ltd., China). Distilled water was used as an additional agent during the hydrothermal process and for the aqueous solutions and washing. The chemicals in the experiment were all analytical grade reagents and were used without further purification. 2.2. Synthesis procedure In a typical experiment, 2.5 g of BaCl2$2H2O was dissolved in 20 mL distilled water with continuous stirring for 15 min. Then, 4.5 g NaOH and 0.3 g C6H8O7·H2O were added into the solution with continuous stirring for 5 min. After that, 5 mL butyl titanate and 5 mL H2O were added into the mixture system. Based on the calculations and actual formulations, 5.0 g of HA powders were dissolved in 30 mL of deionized water, absolute ethyl alcohol (ET), ethylene glycol (EG) and dimethyl formamide (DMF), separately. The suspensions were added into above BT system with ultrasonic dispersion for 30 min. Then, the as-prepared mixture was put into a teflonlined stainless steel-autoclave (100 mL) with a filling volume of 70%. The hydrothermal treatment was conducted at 160 C for 12 h allowing the autoclave to cool to ambient temperature naturally. The deposition was finally filtered, washed with distilled water and absolute ethanol for three times to remove other impurities and dried in a vacuum oven at 60 C for 5 h. Finally, the BT/ HA nanocomposites were obtained.
3. Results and discussion 3.1. XRD and IR analyses Fig. 1 shows the XRD and IR patterns of BT/HA nanocomposites obtained at 160 C for 12 h in different solvents of (a) distilled water solvent (H2O), (b) DMF solvent, (c) ethanol (ET) solvent and (d) ethylene glycol (EG) solvent, respectively. It can be seen that the peaks of cubic structure BaTiO3 (JCPDS card: 31-0174) prepared in different solvent appeared, implying that the crystallized BaTiO3 nanoparticles were formed, and orthogonal structure of BaCO3 (JCPDS card: 05-0378) present in BT/HA distilled water solvent (H2O), DMF solvent and ethylene glycol(EG) solvent with a small amount. The other diffraction peaks were according with the hexagonal structure of HA (JCPDS card: 74-0565). The well-crystalline BT/HA nanocomposites can be prepared in ET solvent. the FTIR
2.3. Characterization X-ray powder diffraction (XRD) patterns of the products were obtained on a Japan Rigaku D/Max-IIIC diffractometer at a voltage of 60 kV and a current of 80 mA with Cu Ka radiation (l ¼ 1.5406 Å), employing a scanning rate of 8 min1 in the 2q ranging from 20 to 70 . Scanning electron microscopy (SEM) micrographs were explored on a JEOL JSM-6700F microscope. Transmission electron microscopy (TEM) micrographs were taken on a JEOL JEM-3010 transmission electron microscope at an accelerating voltage of 200 kV. IR spectra were recorded on a SHIMADZU Prestige-21 FT-IR spectrometer. The measurements were performed on films containing KBr and the sample. 2.4. Electrical measurements The piezoelectric coefficient (d33, which quantifies the volume change when a piezoelectic material is subject to an electric field or the polarization on application of a stress) was measured using a quasi-static d33 m (ZJ-3, Shanghai shiyan technology co., LTD, Shanghai, China). Electrical measurements were carried out using a Solartron frequency response analyzer (TH2818, Changzhou tonghui electronics co., LTD, Changzhou, China) combined with a Solartron dielectric interface (TH2818). A frequency of 1 KHz was employed with an applied voltage of 100 mV. With the experimental set-up capacitances were measured and dielectric constants were calculated from the capacitance data via the equation C ¼ (ℇ0ℇrA)/t with C the capacitance, ℇ0 the dielectric constant of the
Fig. 1. XRD and IR patterns of products obtained indifferent solvents at 140 C for 12 h (a) distilled water solvent (H2O), (b) DMF solvent, (c) ethanol(ET) solvent and (d) ethylene glycol(EG) solvent.
H. Jiao et al. / Journal of Alloys and Compounds 693 (2017) 221e225
spectra of BT/HA nanocomposites synthesized in different solvents, respectively, which shows a number of characteristic bands representing the phosphate group at ~1090, and 1043 cm1 (triply asymmetric stretching mode of the PeO bond) [11]. Additional bands representing a triply degenerated bending mode of the OePeO bond (~601 and 567 cm1) are also observed in the low wave number region. Bands in the 1630e1191 cm1 region indicate the existence of carbonate groups, suggesting their incorporation into the crystal structure of BT/HA, which was possibly due to the absorption of carbon dioxide from the air during the holding time. The intense peak at ~3446 cm1 is assigned to the stretching of the structural hydroxyl anions. BaCO3 is the main impurity of the BaTiO3 powders prepared by the hydrothermal method, and there were apparent absorption peaks 1458 cm1 (the antisymmetric stretching of carbonic acid groups) attributed to BaCO3, which indicates that BaCO3 is existed [15,20]. The one centered at 540 cm1 is due to TieO vibration, and the other at ~430 cm1 is characteristic of BaTiO3. 3.2. SEM analyses Fig. 2aed shows the SEM photographs of BT/HA nanocomposites prepared by hydrothermally in different solvents, respectively. The samples obtained at distilled water solvent (Fig. 2a, b) are irregular reunite spherical particles and the range of sizeis about 50e100 nm. The samples obtained at DMF solvent (Fig. 2c, d) are reunite rod like particles with diameter of 30e40 nm and length of 80e100 nm. The samples obtained at ET solvent (Fig. 2) are uniform rod-like particles, and the average diameter is about 30 nm and length is 150 nm. The samples obtained at EG
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solvent (Fig. 2) are irregular reunite particles. The results show that the morphology of samples can be changed in different solvents. 3.3. TEM analyses of BT/HA nanocomposites Fig. 3 shows the morphology of the sample synthesized in ET solvents at 160 C for 12 h, observed by TEM. It can be seen that the nanocomposites (Fig. 3a, b) are HA nanoparticles with average diameter of 30 nm and BT nanorods with length of 150 nm and diameter of 30 nm. Further structure characterization was carried out by HRTEM. Fig. 3c shows the HRTEM images taken from a single nanoparticle labeled (the rectangular box area in Fig. 3c). The 0.344 nm interval of the lattice fringed observed in the image agrees well with the spacing of the (002) planes of hexagonal structure HA. Fig. 3d shows the HRTEM images taken from a single nanorod labeled (the rectangular box area in Fig. 3c). The 0.284 nm interval of the lattice fringed observed in the image agrees well with the spacing of the (110) planes of cubic structure BaTiO3. From the SAED image in Fig. 3e (the rectangular box area in Fig. 3b), the result shows that nanocomposites are polycrystalline. The major constituents and their distribution in the crystal layer were investigated by EDS, and the spectrum is shown in Fig. 3f. Ca, P, Ba and Ti atoms were clearly detected, indicating that Ca, P, Ba, Ti distributed in the nanocomposites. Additionally, the ratio of Ba and Ca atoms is about 1:10, and the results show the mole ratio of BT/HA is 1:1. 3.4. Electric properties of BT/HA nanocomposites The electric property of BT/HA nanocomposites obtained at 160 C for 12 h in different different solvents of distilled water
Fig. 2. SEM images of products prepared in different solvents. (a) Distilled water solvent (H2O), (b) DMF solvent, (c) ethanol (ET) solvent, (d) ethylene glycol (EG) solvent.
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Fig. 3. TEM, HRTEM, SAED and EDS micrographs of samples synthesized in ET solvents at 140 C for 12 h (a, b) TEM, (c) HRTEM of the BT nanorod, (d) HRTEM of the HA nanoparticle, (e) SAED, (f) EDS.
solvent (H2O), DMF solvent, ethanol (ET) solvent and ethylene glycol (EG) solvent was measured, respectively. Fig. 4a shows the piezoelectric coefficient d33 of the BT/HA nanocomposites. The piezoelectric coefficient of the samples was 2.74, 3.23, 6.88 and 4.20 at the frequency of 1 KHz. The measured dielectric constant of BT/HA nanocomposites is higher than that of conventional mechanical composite of BT/HA powders from 0.3 to 2.8 pC/N [8], indicating that the nanocomposites could increase the piezoelectric coefficient obviously. Fig. 4b shows the measured dielectric constant of the BT/HA nanocomposites. The dielectric constant ε of the samples was 18.45,
21.79, 27.40 and 19.87 with the frequency of 1 KHz. Electrical performance of the BT/HA nanocomposites were decided by the electrical active, size, morphology of BaTiO3 and composite state. Because under the same conditions the ET thermal synthesis of composite product, its crystallinity was higher than in other solvent thermal synthesis. The electrical performance of the product under the ET thermal response will be more superior. The nanoscale BaTiO3 ceramic has more excellent electrical performance because a small amount of BaTiO3 adding can reach the performance requirements.
H. Jiao et al. / Journal of Alloys and Compounds 693 (2017) 221e225
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Fig. 4. Piezoelectric coefficient (a) and dielectric constant (b) of BaTiO3/HA composites obtained at 140 C for 12 h in different solvents of distilled water solvent (H2O), DMF solvent, ethanol (ET) solvent and ethylene glycol (EG) solvent, respectively.
4. Conclusions In this study, BT/HA nanocomposites were successfully fabricated by a hydrothermal method. The different solvents were discussed during preparation process without anyother variations in BT/HA contents. In addition, the BT/HA nanocomposites have a higher piezoelectric coefficient than that of the natural bone. Ethanol solvent can inhibit the hydrolysis of butyl titanate, which is conducive to the production of BT. the results show that the d33 andεvalue were improved when piezoelectric phase in the BT/HA nanocomposites in ethanol solvent was increased. Further research will continue exploring the in vitro reaction with host tissue to determine the most useful combination of the different properties, i.e. mechanical property and piezoelectric property using this BT/ HA nanocomposites. Acknowledgment This work was supported by the National Natural Science Foundation of China (No. 51372199). References [1] P. Kanchana, C. Sekar, Development of electrochemical folic acid sensor based on hydroxyapatite nanoparticles, Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 137 (2015) 58e65. [2] H.L. Fu, M.N. Rahaman, R.F. Brown, D.E. Day, Evaluation of bone regeneration in implants composed of hollow HA microspheres loaded with transforming growth factor b1 in a rat calvarial defect model, Acta Biomater. 9 (2013) 5718e5727. [3] A. Rezaei, M.R. Mohammadi, In vitro study of hydroxyapatite/polycaprolactone (HA/PCL) nanocomposite synthesized by an in situ solegel process, Mater. Sci. Eng. C 33 (2013) 390e396. [4] Z. Fang, Q.L. Feng, R.W. Tan, In-situ grown hydroxyapatite whiskers reinforced porous HA bioceramic, Ceram. Int. 39 (2013) 8847e8852. [5] A. Arifin, A.B.S. Long, N. Muhamad, J. Syarif, M.I. Ramli, Material processing of hydroxyapatite and titanium alloy (HA/Ti) composite as implant materials
using powder metallurgy: a review, Mater. Des. 55 (2014) 165e175. [6] Q. Wang, Q. Chen, J. Zhu, C. Huang, B.W. Darvell, et al., Effects of pore shape and porosity on the properties of porous LNKN ceramics as bone substitute, Mater. Chem. Phys. 109 (2008) 488e491. [7] S.T. Sheng, W. Yu, W.H. Sing, Y.T. Sa, C. Su, Ion release from three lead-free piezoelectric ceramics and their physical and cytotoxicity characteristics, Mater. Lett. 65 (2011) 3522e3524. [8] Y. Zhang, L.J. Chen, J. Zeng, K.C. Zhou, D. Zhang, Aligned porous barium titanate/hydroxyapatite composites with high piezoelectric coefficients for bone tissue engineering, Mater. Sci. Eng. C 39 (2014) 143e149. [9] W.L.W. Lee, W.H. Chung, W.S. Huang, W.C. Lin, W.Y. Lin, Y.R. Jiang, C.C. Chen, Photocatalytic activity and mechanism of nano-cubic barium titanate prepared by a hydrothermal method, J. Taiwan Inst. Chem. Eng. 44 (2013) 660e669. [10] S. Adireddy, C.K. Lin, B.B. Cao, W.L. Zhou, G. Caruntu, Solution-based growth of monodisperse cube-like BaTiO3 colloidal nanocrystals, Chem. Mater. 22 (2010) 1946e1948. [11] T. Yang, Z.D. Gordon, C.K. Chan, Synthesis of hyperbranched perovskite nanostructures, Cryst. Gtowth Des. 13 (2013) 3901e3907. [12] Z. Zhou, H.X. Tang, H.A. Sodano, Vertically aligned arrays of BaTiO3 nanowires, ACS Appl. Mater. Interfaces 5 (2013) 11894e11899. [13] M. Natsume, J.H. Kim, S. Yonezawa, M. Takashima, Preparation and characterization of nano-sized BaTiO3 particles using aqueous peroxotitanium acid solution: effects of pH adjustment, Mater. Chem. Phys. 148 (2014) 169e174. [14] S. Ramakanth, K.C.J. Raju, Charge transfer induced magnetism in solegel derived nanocrystalline BaTiO3, Solid State Commun. 187 (2014) 59e63. [15] B. Xiao, W. Zheng, Y.L. Dong, N. Ma, P.Y. Du, Multiferroic ceramic composite with in situ glassy barrier interface and novel electromagnetic properties, J. Phys. Chem. C 118 (2014) 5802e5809. [16] W.W. Wang, L.X. Cao, W. Liu, G. Su, W.X. Zhang, Low-temperature synthesis of BaTiO3 powders by the solegel-hydrothermal method, Ceram. Int. 39 (2013) 7127e7134. [17] X. Yang, Z.H. Ren, G. Xu, C.Y. Chao, S. Jiang, S.Q. Deng, G. Shen, X. Wei, G.R. Han, Monodisperse hollow perovskite BaTiO3 nanostructures prepared by a solegelehydrothermal method, Ceram. Int. 40 (2014) 9663e9670. [18] Y. Zhang, Y. Liu, X.B. Ji, Fabrication of flower-like hydroxyapatite agglomerates with the assistant of bamboo membrane, Mater. Lett. 65 (2011) 1982e1985. [19] K.C. Huang, T.C. Huang, W.F. Hsieh, Morphology-controlled synthesis of barium titanate nanostructures, Inorg. Chem. 48 (2009) 9180e9184. [20] B.R. Li, W. Shang, Z.L. Hu, N.Q. Zhang, Template-free fabrication of pure singlecrystalline BaTiO3 nano-wires by molten salt synthesis technique, Ceram. Int. 40 (2014) 73e80.
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Preparation and characterization of BaTiO3/HA nanocomposite materials by hydrothermal synthesis Hua Jiao, Kang Zhao*, Lining Ma, Yufei Tang, Xiao Liu, Tierong Bian School of Materials Science and Engineering, Xi'an University of Technology, Xi'an, 710048, China
a r t i c l e i n f o
a b s t r a c t
Article history: Received 24 July 2016 Received in revised form 1 September 2016 Accepted 17 September 2016 Available online 19 September 2016
It was proposed that the piezoelectric effect played an important physiological role in bone growth, remodeling and fracture healing. Barium titanate/hydroxyapatite (BT/HA) nanorods piezoelectric composite was fabricated by hydrothermal process using 30 nm HA dissolved in different solvents (H2O, DMF, ethanol and ethylene glycol), and then reacted in the BaCl2, C6H8O7, butyl titanate mixture solution, respectively. The samples were characterized by XRD, IR, SEM and TEM to obtain sizes and crystal structure. The results showed that the BT/HA rod-like particles can be obtained at ethanol solvent, and the average diameter is about 30 nm and length is 150 nm. Meanwhile, BT/HA nanorod composites obtained at different solvents exhibited both good dielectric constant ε (18.45, 21.79, 27.40, 19.87), and piezoelectric coefficient d33 (2.74, 3.23, 6.88, 4.20), which were all higher than the piezoelectric coefficient of natural bone. The ε and d33 were improved by increasing the BT in ethanol solvent. © 2016 Elsevier B.V. All rights reserved.
Keywords: Nanorod composites Piezoelectric ceramics Hydroxyapatite/barium titanate Hydrothermal
1. Introduction Hydroxyapatite (HA) is chemically similar to the inorganic component of bone matrix with general formula Ca10(OH)2(PO4)6. HA particles on nanometric scale have been proved to be an osteo conductive material that also chemically binds to enamel and dentine [1]. HA is an attractive material for applications in the bone regeneration field due to its biological characteristics, such as being the major inorganic component of the bone matrix, its specific affinity toward many adhesive proteins, and its direct involvement in the bone cell differentiation and mineralization processes [2]. The close chemical similarity of HA to natural bone has led to extensive research efforts to use synthetic HA as a bone substitute and/or replacement in biomedical applications [3,4]. However, it shows poor biomechanical properties such as high brittleness, low fatigue strength and low flexibility [5]. Therefore, it is not suitable for direct-loading applications as well as application of dynamic force during the in vitro bone tissue engineering process. Due to the environment and biocompatibility concerns, many efforts were made to improve the bone healing response by using lead free piezoelectric ceramics, such as (Li0.06Na0.5K0.44)NbO3 (LNKN) [6], potassium sodium niobate (KNN) [7] and barium
* Corresponding author. E-mail address: [email protected] (K. Zhao). http://dx.doi.org/10.1016/j.jallcom.2016.09.175 0925-8388/© 2016 Elsevier B.V. All rights reserved.
titanate [8]. Barium titanate (BaTiO3, BT) is the most studied leadfree material used in the bone replacement and repair for more than 30 years. It exhibits excellent biocompatibility, and ability to form a strong interfacial strength with bone [8]. So far, all the piezoelectric ceramics used in vivo and vitro were in the dense bulk form. Recent advances in nanoscience and nanotechnology have reignited interest in the formation of nanosized HA and nanosized BaTiO3 using hydrothermal method [9e12], coprecipitation [13], sol-gel [14,15], sol - gel - hydrothermal method [16,17], template method [11,18] and molten salt method [19,20] to study of its properties on the nanoscale. Zhang et al. [8]. Has reported HA/ BaTiO3 piezoelectric composites which were fabricated by freeze casting hydroxyapatite/barium titanate (BT/HA) suspensions with the HA of 1 mm and BaTiO3 of 0.29 mm. The results of HA30/BT70 and HA10/BT90 composites exhibited piezoelectric coefficient d33 of 1.2 and 2.8 pC/N, respectively. To our best of knowledge, there is no report so far on the piezoelectric properties of nanosized BT/HA piezoelectric composites. In this study, BT/HA nanocomposites were obtained by a hydrothermal method. In order to provide the thorough information and find the most useful combination of the different properties used for the morphologies, piezoelectric and mechanical properties were investigated according to the processing parameters, i.e. BT/HA in different solvents.
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2. Experimental
free space (8.85 1012 F m1). A the area of the dielectric, t the thickness and ℇr is the dielectric constant of samples.
2.1. Materials Butyl titanate (C16H36O4Ti (Ti(OeBu)4)), (Tianjin Chemical Reagent Factory, China), and barium chloride dihydrate (BaCl2$2H2O) (Xi'an Chemical Reagent Factory, China)were used as the raw materials. Sodium hydroxide (NaOH) (Xi'an Reagent Factory, China) and citric acid (C6H8O7$H2O) (Tianjin Chemical Reagent Factory, China) was used as a mineralizer. HA powder with the median grain size d ¼ 30 nm and a purity of 99% (according to the manufacturer's data, Nanjing Emperor Nano Material Co., Ltd., China). Distilled water was used as an additional agent during the hydrothermal process and for the aqueous solutions and washing. The chemicals in the experiment were all analytical grade reagents and were used without further purification. 2.2. Synthesis procedure In a typical experiment, 2.5 g of BaCl2$2H2O was dissolved in 20 mL distilled water with continuous stirring for 15 min. Then, 4.5 g NaOH and 0.3 g C6H8O7·H2O were added into the solution with continuous stirring for 5 min. After that, 5 mL butyl titanate and 5 mL H2O were added into the mixture system. Based on the calculations and actual formulations, 5.0 g of HA powders were dissolved in 30 mL of deionized water, absolute ethyl alcohol (ET), ethylene glycol (EG) and dimethyl formamide (DMF), separately. The suspensions were added into above BT system with ultrasonic dispersion for 30 min. Then, the as-prepared mixture was put into a teflonlined stainless steel-autoclave (100 mL) with a filling volume of 70%. The hydrothermal treatment was conducted at 160 C for 12 h allowing the autoclave to cool to ambient temperature naturally. The deposition was finally filtered, washed with distilled water and absolute ethanol for three times to remove other impurities and dried in a vacuum oven at 60 C for 5 h. Finally, the BT/ HA nanocomposites were obtained.
3. Results and discussion 3.1. XRD and IR analyses Fig. 1 shows the XRD and IR patterns of BT/HA nanocomposites obtained at 160 C for 12 h in different solvents of (a) distilled water solvent (H2O), (b) DMF solvent, (c) ethanol (ET) solvent and (d) ethylene glycol (EG) solvent, respectively. It can be seen that the peaks of cubic structure BaTiO3 (JCPDS card: 31-0174) prepared in different solvent appeared, implying that the crystallized BaTiO3 nanoparticles were formed, and orthogonal structure of BaCO3 (JCPDS card: 05-0378) present in BT/HA distilled water solvent (H2O), DMF solvent and ethylene glycol(EG) solvent with a small amount. The other diffraction peaks were according with the hexagonal structure of HA (JCPDS card: 74-0565). The well-crystalline BT/HA nanocomposites can be prepared in ET solvent. the FTIR
2.3. Characterization X-ray powder diffraction (XRD) patterns of the products were obtained on a Japan Rigaku D/Max-IIIC diffractometer at a voltage of 60 kV and a current of 80 mA with Cu Ka radiation (l ¼ 1.5406 Å), employing a scanning rate of 8 min1 in the 2q ranging from 20 to 70 . Scanning electron microscopy (SEM) micrographs were explored on a JEOL JSM-6700F microscope. Transmission electron microscopy (TEM) micrographs were taken on a JEOL JEM-3010 transmission electron microscope at an accelerating voltage of 200 kV. IR spectra were recorded on a SHIMADZU Prestige-21 FT-IR spectrometer. The measurements were performed on films containing KBr and the sample. 2.4. Electrical measurements The piezoelectric coefficient (d33, which quantifies the volume change when a piezoelectic material is subject to an electric field or the polarization on application of a stress) was measured using a quasi-static d33 m (ZJ-3, Shanghai shiyan technology co., LTD, Shanghai, China). Electrical measurements were carried out using a Solartron frequency response analyzer (TH2818, Changzhou tonghui electronics co., LTD, Changzhou, China) combined with a Solartron dielectric interface (TH2818). A frequency of 1 KHz was employed with an applied voltage of 100 mV. With the experimental set-up capacitances were measured and dielectric constants were calculated from the capacitance data via the equation C ¼ (ℇ0ℇrA)/t with C the capacitance, ℇ0 the dielectric constant of the
Fig. 1. XRD and IR patterns of products obtained indifferent solvents at 140 C for 12 h (a) distilled water solvent (H2O), (b) DMF solvent, (c) ethanol(ET) solvent and (d) ethylene glycol(EG) solvent.
H. Jiao et al. / Journal of Alloys and Compounds 693 (2017) 221e225
spectra of BT/HA nanocomposites synthesized in different solvents, respectively, which shows a number of characteristic bands representing the phosphate group at ~1090, and 1043 cm1 (triply asymmetric stretching mode of the PeO bond) [11]. Additional bands representing a triply degenerated bending mode of the OePeO bond (~601 and 567 cm1) are also observed in the low wave number region. Bands in the 1630e1191 cm1 region indicate the existence of carbonate groups, suggesting their incorporation into the crystal structure of BT/HA, which was possibly due to the absorption of carbon dioxide from the air during the holding time. The intense peak at ~3446 cm1 is assigned to the stretching of the structural hydroxyl anions. BaCO3 is the main impurity of the BaTiO3 powders prepared by the hydrothermal method, and there were apparent absorption peaks 1458 cm1 (the antisymmetric stretching of carbonic acid groups) attributed to BaCO3, which indicates that BaCO3 is existed [15,20]. The one centered at 540 cm1 is due to TieO vibration, and the other at ~430 cm1 is characteristic of BaTiO3. 3.2. SEM analyses Fig. 2aed shows the SEM photographs of BT/HA nanocomposites prepared by hydrothermally in different solvents, respectively. The samples obtained at distilled water solvent (Fig. 2a, b) are irregular reunite spherical particles and the range of sizeis about 50e100 nm. The samples obtained at DMF solvent (Fig. 2c, d) are reunite rod like particles with diameter of 30e40 nm and length of 80e100 nm. The samples obtained at ET solvent (Fig. 2) are uniform rod-like particles, and the average diameter is about 30 nm and length is 150 nm. The samples obtained at EG
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solvent (Fig. 2) are irregular reunite particles. The results show that the morphology of samples can be changed in different solvents. 3.3. TEM analyses of BT/HA nanocomposites Fig. 3 shows the morphology of the sample synthesized in ET solvents at 160 C for 12 h, observed by TEM. It can be seen that the nanocomposites (Fig. 3a, b) are HA nanoparticles with average diameter of 30 nm and BT nanorods with length of 150 nm and diameter of 30 nm. Further structure characterization was carried out by HRTEM. Fig. 3c shows the HRTEM images taken from a single nanoparticle labeled (the rectangular box area in Fig. 3c). The 0.344 nm interval of the lattice fringed observed in the image agrees well with the spacing of the (002) planes of hexagonal structure HA. Fig. 3d shows the HRTEM images taken from a single nanorod labeled (the rectangular box area in Fig. 3c). The 0.284 nm interval of the lattice fringed observed in the image agrees well with the spacing of the (110) planes of cubic structure BaTiO3. From the SAED image in Fig. 3e (the rectangular box area in Fig. 3b), the result shows that nanocomposites are polycrystalline. The major constituents and their distribution in the crystal layer were investigated by EDS, and the spectrum is shown in Fig. 3f. Ca, P, Ba and Ti atoms were clearly detected, indicating that Ca, P, Ba, Ti distributed in the nanocomposites. Additionally, the ratio of Ba and Ca atoms is about 1:10, and the results show the mole ratio of BT/HA is 1:1. 3.4. Electric properties of BT/HA nanocomposites The electric property of BT/HA nanocomposites obtained at 160 C for 12 h in different different solvents of distilled water
Fig. 2. SEM images of products prepared in different solvents. (a) Distilled water solvent (H2O), (b) DMF solvent, (c) ethanol (ET) solvent, (d) ethylene glycol (EG) solvent.
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Fig. 3. TEM, HRTEM, SAED and EDS micrographs of samples synthesized in ET solvents at 140 C for 12 h (a, b) TEM, (c) HRTEM of the BT nanorod, (d) HRTEM of the HA nanoparticle, (e) SAED, (f) EDS.
solvent (H2O), DMF solvent, ethanol (ET) solvent and ethylene glycol (EG) solvent was measured, respectively. Fig. 4a shows the piezoelectric coefficient d33 of the BT/HA nanocomposites. The piezoelectric coefficient of the samples was 2.74, 3.23, 6.88 and 4.20 at the frequency of 1 KHz. The measured dielectric constant of BT/HA nanocomposites is higher than that of conventional mechanical composite of BT/HA powders from 0.3 to 2.8 pC/N [8], indicating that the nanocomposites could increase the piezoelectric coefficient obviously. Fig. 4b shows the measured dielectric constant of the BT/HA nanocomposites. The dielectric constant ε of the samples was 18.45,
21.79, 27.40 and 19.87 with the frequency of 1 KHz. Electrical performance of the BT/HA nanocomposites were decided by the electrical active, size, morphology of BaTiO3 and composite state. Because under the same conditions the ET thermal synthesis of composite product, its crystallinity was higher than in other solvent thermal synthesis. The electrical performance of the product under the ET thermal response will be more superior. The nanoscale BaTiO3 ceramic has more excellent electrical performance because a small amount of BaTiO3 adding can reach the performance requirements.
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Fig. 4. Piezoelectric coefficient (a) and dielectric constant (b) of BaTiO3/HA composites obtained at 140 C for 12 h in different solvents of distilled water solvent (H2O), DMF solvent, ethanol (ET) solvent and ethylene glycol (EG) solvent, respectively.
4. Conclusions In this study, BT/HA nanocomposites were successfully fabricated by a hydrothermal method. The different solvents were discussed during preparation process without anyother variations in BT/HA contents. In addition, the BT/HA nanocomposites have a higher piezoelectric coefficient than that of the natural bone. Ethanol solvent can inhibit the hydrolysis of butyl titanate, which is conducive to the production of BT. the results show that the d33 andεvalue were improved when piezoelectric phase in the BT/HA nanocomposites in ethanol solvent was increased. Further research will continue exploring the in vitro reaction with host tissue to determine the most useful combination of the different properties, i.e. mechanical property and piezoelectric property using this BT/ HA nanocomposites. Acknowledgment This work was supported by the National Natural Science Foundation of China (No. 51372199). References [1] P. Kanchana, C. Sekar, Development of electrochemical folic acid sensor based on hydroxyapatite nanoparticles, Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 137 (2015) 58e65. [2] H.L. Fu, M.N. Rahaman, R.F. Brown, D.E. Day, Evaluation of bone regeneration in implants composed of hollow HA microspheres loaded with transforming growth factor b1 in a rat calvarial defect model, Acta Biomater. 9 (2013) 5718e5727. [3] A. Rezaei, M.R. Mohammadi, In vitro study of hydroxyapatite/polycaprolactone (HA/PCL) nanocomposite synthesized by an in situ solegel process, Mater. Sci. Eng. C 33 (2013) 390e396. [4] Z. Fang, Q.L. Feng, R.W. Tan, In-situ grown hydroxyapatite whiskers reinforced porous HA bioceramic, Ceram. Int. 39 (2013) 8847e8852. [5] A. Arifin, A.B.S. Long, N. Muhamad, J. Syarif, M.I. Ramli, Material processing of hydroxyapatite and titanium alloy (HA/Ti) composite as implant materials
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