Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 268–273
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Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Controlling of dielectrical properties of hydroxyapatite by ethylenediamine tetraacetic acid (EDTA) for bone healing applications Omer Kaygili a,⇑, Tankut Ates a, Serhat Keser b, Ahmed A. Al-Ghamdi c, Fahrettin Yakuphanoglu a,c a
Department of Physics, Faculty of Science, Firat University, 23119 Elazig, Turkey Department of Chemistry, Faculty of Science, Firat University, 23119 Elazig, Turkey c Department of Physics, Faculty of Sciences, King Abdulaziz University, Jeddah, Saudi Arabia b
g r a p h i c a l a b s t r a c t
The amount of EDTA affects the lattice
20
1.0 1 kHz 2 MHz
18 16
E3
1 kHz 2 MHz
E3
0.8
E1
E1
0.6
ε'
ε"
14
E0
0.4
12 0.2
E0
10
E2
0.0
8 20
22
24
26
28
30
22
24
1 kHz 2 MHz
26
−1
4
3
E0 E2
2 0.0000
E0
E2 20
22
24
26
28
30
1 32
D (nm)
i n f o
Article history: Received 8 February 2014 Received in revised form 3 March 2014 Accepted 21 March 2014 Available online 3 April 2014 Keywords: Hydroxyapatite Sol–gel preparation Crystal structure Dielectric property
22
24
26
28
30
32
D (nm)
The hydroxyapatite (HAp) samples in the presence of various amounts of ethylenediamine tetraacetic acid (EDTA) were prepared by sol–gel method. The effects of EDTA on the crystallinity, phase structure, chemical, micro-structural and dielectric properties of HAp samples were investigated. With the addition of EDTA, the average crystallite size of the HAp samples is gradually decreased from 30 to 22 nm and the crystallinity is in the range of 65–71%. The values of the lattice parameters (a and c) and volume of the unit cell are decreased by stages with the addition of EDTA. The dielectric parameters such as relative permittivity, dielectric loss and relaxation time are affected by the adding of EDTA. The alternating current conductivity of the as-synthesized hydroxyapatites increases with the increasing frequency and obeys the universal power law behavior. The HAp samples exhibit a non-Debye relaxation mechanism. The obtained results that the dielectrical parameters of the HAp sample can be controlled by EDTA. Ó 2014 Elsevier B.V. All rights reserved.
Hydroxyapatite (HAp), which is a member of the calcium phosphate family, is one of the most known biomaterials, and its chemical formula is Ca10(PO4)6(OH)2 [1–3]. The crystal structure of HAp is hexagonal and its lattice parameters are a = b = 0.9418 nm and ⇑ Corresponding author. Tel.: +90 424 2370000x3623; fax: +90 424 2330062.
http://dx.doi.org/10.1016/j.saa.2014.03.082 1386-1425/Ó 2014 Elsevier B.V. All rights reserved.
20
a b s t r a c t
Introduction
E-mail address: okaygili@firat.edu.tr (O. Kaygili).
32
E3 0.0010
0.0005
a r t i c l e
30
E1
5
0.0015
28
D (nm)
6
E1
E3
E2 20
32
D (nm)
0.0020
σac (S m )
parameters of a and c. The average crystallite size is gradually decreased from 30 to 22 nm. The crystallinity is in the range of 65–71%. Ca/P ratio is higher than the value of 1.67 for EDTA-containing samples.
εο− ε∞
h i g h l i g h t s
c = 0.6884 nm [4,5]. The compositional similarity of HAp with the hard tissues of vertebrates such as bone and teeth makes it very attractive in dental and medical applications as an implant material [6,7]. HAp has a number of excellent properties, including non-toxicity, non-inflammatory, high bioactivity, biocompatibility, osteoconductivity, bone-bonding, chemical stability, resistance to corrosion, low electrical and thermal conductivity, as well as low cost of production [8,9]. On the other hand, HAp has poor mechanical properties in comparison to human bones. Because of this
269
Materials and methods For the synthesis of HAp samples, 0.5 M Ca(NO3)24H2O and 0.3 M (NH4)2HPO4 were separately dissolved in 100 ml of distilled water in two beakers. These solutions were mixed together and were stirred using a magnetic stirrer. 0.01 M EDTA solution in the different amounts (0, 2, 10 and 40 ml) was added to this solution and these samples were named as E0, E1, E2 and E3, respectively. Then, pH of the solution was adjusted to 10 by adding NH4OH. The final solutions were vigorously mixed at 85 °C for 6 h until the beginning of gelation. The obtained gels were kept at 120 °C during 2 h in a furnace and then, the temperature was increased to 180 °C and the obtained gels were dried for 2 h and were heated at 700 °C for 2 h. The crystal structure and the phase analysis of the samples were carried out using X-ray diffraction (XRD) instrument (Bruker D8 Advance). Fourier transform infrared (FTIR) spectra of the samples were recorded by PerkinElmer Spectrum One spectrophotometer. The structural properties of the samples were investigated using a scanning electron microscope (SEM, LEO EVO 40). The dielectric properties were studied using a HIOKI 3532-50 LCR meter at room temperature.
200 150 100 50 0 200 150 100 50 0 200 150 100 50 0 200 150 100 50 0
E2
25
(112)
30
45
(213) (321) (410) (402) (004)
(222)
(312)
(113)
40
(203)
(310)
35
(311)
(202)
(300)
E0
(301)
(102) (210)
(002)
(211)
E1
20
50
55
o
2θ ( ) Fig. 1. XRD patterns of the as-prepared samples.
size is due to the increasing amount of EDTA, because the amount EDTA increases the dissolution rate of Ca(NO3)24H2O and (NH4)2HPO4 precursors in the distilled water during the formation of gels. The dissolution rate changes the size of nucleolus during the nucleation stage of the particles and in turn, the particle size is decreased with EDTA amount. The obtained average crystallite size values suggest that all the samples have the nanostructure. The nanosize is controlled with addition of EDTA into the HAp. The crystallinity (XC) of HAp samples was calculated according to Landi et al. [27]. The crystallinity values of the samples are found to be 70%, 71%, 65% and 65% for E0, E1, E2 and E3, respectively. The crystallinity of pure-HAp is very close to that of the calculated value for HAp (75%) by Qian et al. [28] and it is changed with the addition of EDTA into HAp. The lattice parameters (a and c) and volume of the unit cell (V) of the HAp samples were determined by the following relations [29]: Table 1 The calculated values of the lattice parameters and the volume of the unit cell. Sample
a (nm)
c (nm)
V (nm3)
E0 E1 E2 E3
0.9373 0.9434 0.9384 0.9373
0.6833 0.6890 0.6864 0.6838
0.5199 0.5310 0.5234 0.5202
60 30
Results and discussion
E3
0 60
Transmittance (%)
XRD patterns of the samples are shown in Fig. 1. All the diffraction peaks agree with the hexagonal HAp (JCPDS No: 09-432). The secondary phases of b-TCP (tricalcium phosphate) and CaO were not observed in the XRD patterns, and this result confirms that EDTA-assisted HAp samples are pure materials. The narrow peaks in the XRD patterns indicate the high crystalline structure. Additionally, the XRD patterns show that all the samples compose of the randomly oriented crystals. Scherrer relation was used to calculate average crystallite size, D, of the samples [26]. (0 0 2) and (2 1 1) planes were chosen for calculating the average crystallite size and the obtained values are 29.45, 26.82, 26.14 and 22.23 nm for E0, E1, E2 and E3, respectively. With the addition of EDTA into the HAp, the average crystallite size decreases from 30 to 22 nm. The decrease in the particle
E3
(200) (111)
drawback, the clinical use of HAp as a load-bearing implant is limited [10]. The preparation of HAp has been employed by several methods, including hydrothermal, solid-state reaction, spray pyrolysis and sol–gel techniques [11–17]. In comparison to the other methods; sol–gel offers some advantages, including easily preparation, high purity, nanostructure and low synthesis temperatures [18–20]. Ethylenediamine tetraacetic acid (EDTA), which is a very important and well-known analytical reagent, has been used as the chelating agent that influences cell–cell contacts regulated by Ca2+ ions. EDTA is also used to control the nucleation and growth mechanisms of HAp crystals [21–23]. Although the effects of EDTA on the as-mentioned above properties of HAp were investigated, there was no article related to the detailed study of the electrical and dielectric properties of EDTA-assisted HAp samples. Of course, one of the most desired properties for a material, which can be used for bone application, is to have the same electrical and dielectric properties like bone since these properties are more important for bone healing applications [24,25]. Thus, in order to control the dielectric properties of the HAP, we synthesized the hydroxyapatite (HAp) in the presence of various molar concentration of ethylenediamine tetraacetic acid to control the crystallize size, crystallization and dielectric parameters. The structural, crystallinity and dielectrical properties of HAp samples were investigated and the obtained results were analyzed in detail.
Intensity (Counts)
O. Kaygili et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 268–273
E2
30 0 60 30
E1
0 60
E0
30 0 4000 3600 3200 2800 2400 2000 1600 1200
Wavenumber (cm−1) Fig. 2. FTIR spectra of all the samples.
800
400
270
O. Kaygili et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 268–273
Fig. 3. SEM images and EDX spectrum of pure-HAp and EDTA-assisted HAp samples.
1 2
d
2
¼
2
2
4ðh þ hk þ k Þ l þ 2 3a2 c
V ¼ 0:866a2 c
ð1Þ ð2Þ
where d is the distance for two adjacent planes, and h, k and l are the Miller indices. The calculated values of a, c and V of the samples are given in Table 1. By the adding EDTA, both lattice parameters and volume of the unit cell are gradually decreased for EDTA assisted HAp samples. The FTIR spectra of all the samples are shown in Fig. 2. The bands at 566, 601, 962, 1034 and 1090 cm1 are associated to
the bending and stretching modes of the phosphate groups. The bands at 632 and 3571 cm1 are attributed to the bending and stretching modes of the hydroxyl group [30,31]. The bands at 1637 and 3445 cm1 are assigned to the adsorbed water. In the spectra obtained by FTIR analyses, the phosphate peaks became sharper and split in the range of 566–1090 cm1 [32,33]. These findings confirm the high crystallinity and support the XRD results. Fig. 3 shows the SEM images and energy dispersive X-ray (EDX) analysis results of all the HAp samples. SEM images show the different morphologies and there is a distribution of small particles and large agglomerates. Ca, P and O were detected by EDX analysis and this result confirms that all the samples did not include any
271
O. Kaygili et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 268–273 3.5
impurity. The Ca/P ratios for the samples were found to be 1.71, 2.18, 2.18 and 2.13 for E0, E1, E2 and E3, respectively. The Ca/P ratio (1.71) of E0 sample is close to the stoichiometric ratio for HAp (1.67). The Ca/P ratio increases with the addition of EDTA. This result can be explained as follows. Some chemicals such as EDTA and citric acid have the altering effects on the chemical structure of dentine [34,35]. It is an expected result that the amount of EDTA affects evidently the chemical composition of HAp since HAp has similar composition of bones and teeth [6,7]. The relative permittivity (e0 ), dielectric loss (e00 ) and alternating current conductivity (rac) values of the samples were calculated by the following relations [36,37]:
Cl
ε"
2.0
e00 ¼ tan d e0
0.5 0.0 2.0M
ð5Þ
where eo is the permittivity of free space, A is the area of the electrode and C and l are the capacitance and thickness of the sample, respectively. tan d is the loss tangent and Z is the impedance of the sample. The plots of the relative permittivity vs. frequency are shown in Fig. 4. The e0 values of the samples at 1 kHz are found to be 12.78, 15.77, 10.32 and 14.34 for E0, E1, E2 and E3, respectively, and are in good agreement with the reported values in the literature for the synthetic hydroxyapatites and different bone species [38–41]. The amount of EDTA significantly affects the relative permittivity. The change in the relative permittivity values is due to the ionic polarization [42]. The EDTA changes the ionic polarization of the HAp sample and in turn, the dipole moment of the HAp sample is changed with the EDTA contents. Thus, the change in dipole moment causes a change in the relative permittivity. The relative permittivity (e0 ) values of the samples indicate a non-linear variation with EDTA content. This non-linear variation of relative permittivity with EDTA content is resulted from the particles sizes of the samples. The change in dielectric parameters of the HAp sample in the presence of EDTA can be attributed to the nanosize of the particles. The nanosize particles change ionic polarization of the HAp and thus, relative permittivity is changed. The plots of the dielectric loss as a function of frequency are shown in Fig. 5. As seen in Fig. 5, the e00 values are changed with adding of EDTA. The dielectric loss plots exhibits a relaxation peak and its position did not shift with EDTA amount. This suggests that the relaxation time did not significantly change with EDTA content, but, the dielectric constants are changed. The relaxation peak indicates the presence of a dielectric relaxation mechanism in the samples. In order to analyze the
2.5M
3.0M
3.5M
4.0M
4.5M
5.0M
f (Hz) Fig. 5. Plots of the dielectric loss as a function of frequency.
ð4Þ
l ZA
1.5 1.0
ð3Þ
eo A
rac ¼
2.5
dielectric relaxation mechanism of the samples, we used the following Cole–Cole relation [43,44]:
e e1 ¼
eo e1 1a 1 þ ðixso Þ
ð6Þ
where e* is the complex dielectric constant, eo and e1 are the ‘‘static’’ and ‘‘infinite frequency or optical’’ dielectric constants, so is the relaxation time and a is an exponent (0 < a < 1). The Cole–Cole plots of the samples are shown in Fig. 6. The values of the e1, eo, eo e1 (De, known as the dielectric strength), a and so parameters were calculated and are given in Table 2. The a value is changed with EDTA amount. As seen in Fig. 6, when a increases, the semi-circle is depressed [45]. The so values for EDTA assisted samples are a slightly lower than that of the pure-HAp. The obtained a values suggest that the samples exhibited a non-Debye relaxation mechanism. In this mechanism, electric dipole is interacted with each other and they have the same constant time. The diameter of Cole–Cole curves of the samples is changed with EDTA content. This means that the electric dipoles are interacted with each other and this causes a change in the dielectric dipole moment and in turn, the relative
3.0
E0 E1 E2 E3
2.5
ε"
e0 ¼
E0 E1 E2 E3
3.0
2.0
1.5
20
E0 E1 E2 E3
16
1.0 10
11
12
13
14
15
16
17
18
19
20
ε'
ε'
Fig. 6. Cole–Cole plots of the samples. 12
Table 2 The calculated values of the e1, eo, eo e1, a and so. 8 2.0M
2.5M
3.0M
3.5M
4.0M
4.5M
5.0M
f (Hz) Fig. 4. Relative permittivity vs. frequency plots of the as-synthesized samples.
Sample
e1
eo
eo e1
a
so (ns)
E0 E1 E2 E3
11.45 15.13 9.91 13.93
14.79 19.67 12.61 17.95
3.34 4.54 2.70 4.02
0.033 0.057 0.020 0.036
34.62 34.58 34.54 34.54
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O. Kaygili et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 268–273 20
1.0
1 kHz 2 MHz
18
E3
E1
0.6
14
ε"
ε'
16
E3
0.8
E1
1 kHz 2 MHz
E0
0.4 12 0.2
E0
10
E2 20
22
24
E2
0.0
8 26
28
30
20
32
22
24
D (nm) -3
30
32
6
E1
E3
28
D (nm)
2.0x10
-3
26
1 kHz 2 MHz
E1
5
1.5x10
-3
1.0x10
ε ο− ε ∞
σac (S/m)
E3
-4
5.0x10
4
3
E0 E2
2 0.0
E0
E2
1 20
22
24
26
28
30
32
20
D (nm)
22
24
26
28
30
32
D (nm)
Fig. 7. Calculated values of the relative permittivity, dielectric loss, alternating current conductivity and dielectric strength at 1 kHz and 2 MHz as a function of the crystallite size.
6x10
E0 E1 E2 E3
5x10 -3
σac (S/m)
where rdc is the direct current conductivity, B is a constant, x is the angular frequency and s is an exponent. The s values calculated from the slope of log rac vs. log x plot were found to be 1.003, 1.004, 1.003 and 1.003 for E0, E1, E2 and E3, respectively. All the s values are higher slightly than 1. This suggests that alternating current conductivity mechanism of the samples is taken place with hopping process conduction mechanism [47,48]. Also, the samples exhibited a non-Debye relaxation mechanism and this confirms that the movement of charge carriers is occurred via hopping process among localized states [49].
-3
4x10 -3
3x10 -3
2x10 -3
1x10
Conclusions
-3
2.0M
2.5M
3.0M
3.5M
4.0M
4.5M
5.0M
f (Hz) Fig. 8. Plots of the alternating current conductivity vs. frequency.
permittivity and dielectric loss values of the samples are changed. As can be seen from Fig. 7, the values of the relative permittivity, dielectric loss, alternating current conductivity and dielectric strength are closely related with the crystallite size. The relaxation strengths (De) values of the samples are changed non-monotonously with EDTA content. The change in De values is due to the change in effective dipole moment. As can be seen from Fig. 8, the rac values increase with increasing frequency. The determination of the conductivity mechanism of the samples was carried out using the well known Jonscher relation [46]
rac ¼ rdc þ Bxs
ð7Þ
EDTA assisted HAp samples without any impurities were successfully prepared by sol–gel method. The lattice parameters (a and c) and volume (V) of the unit cell values are gradually decreased by the addition of EDTA, as well as the average crystallite size. The microstructure of HAp sample was changed with the presence of EDTA in apatitic structure. For EDTA-containing samples, Ca/P ratio is higher than that of the standard value of HAp (1.67). By the adding EDTA, the values of the relative permittivity, dielectric loss and alternating current conductivity are significantly changed. The rac values increase with increasing frequency and obey the universal power law behavior. Additionally, the relaxation time and dielectric strength are affected by the amount of EDTA, as well as the parameters of e1 and eo. The obtained results indicate that the addition of EDTA affects all the above-mentioned parameters. The crystallite size, both lattice parameters, volume of the unit cell and dielectric properties can be easily controlled by the helping of analytical EDTA reagent.
O. Kaygili et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 268–273
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Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Controlling of dielectrical properties of hydroxyapatite by ethylenediamine tetraacetic acid (EDTA) for bone healing applications Omer Kaygili a,⇑, Tankut Ates a, Serhat Keser b, Ahmed A. Al-Ghamdi c, Fahrettin Yakuphanoglu a,c a
Department of Physics, Faculty of Science, Firat University, 23119 Elazig, Turkey Department of Chemistry, Faculty of Science, Firat University, 23119 Elazig, Turkey c Department of Physics, Faculty of Sciences, King Abdulaziz University, Jeddah, Saudi Arabia b
g r a p h i c a l a b s t r a c t
The amount of EDTA affects the lattice
20
1.0 1 kHz 2 MHz
18 16
E3
1 kHz 2 MHz
E3
0.8
E1
E1
0.6
ε'
ε"
14
E0
0.4
12 0.2
E0
10
E2
0.0
8 20
22
24
26
28
30
22
24
1 kHz 2 MHz
26
−1
4
3
E0 E2
2 0.0000
E0
E2 20
22
24
26
28
30
1 32
D (nm)
i n f o
Article history: Received 8 February 2014 Received in revised form 3 March 2014 Accepted 21 March 2014 Available online 3 April 2014 Keywords: Hydroxyapatite Sol–gel preparation Crystal structure Dielectric property
22
24
26
28
30
32
D (nm)
The hydroxyapatite (HAp) samples in the presence of various amounts of ethylenediamine tetraacetic acid (EDTA) were prepared by sol–gel method. The effects of EDTA on the crystallinity, phase structure, chemical, micro-structural and dielectric properties of HAp samples were investigated. With the addition of EDTA, the average crystallite size of the HAp samples is gradually decreased from 30 to 22 nm and the crystallinity is in the range of 65–71%. The values of the lattice parameters (a and c) and volume of the unit cell are decreased by stages with the addition of EDTA. The dielectric parameters such as relative permittivity, dielectric loss and relaxation time are affected by the adding of EDTA. The alternating current conductivity of the as-synthesized hydroxyapatites increases with the increasing frequency and obeys the universal power law behavior. The HAp samples exhibit a non-Debye relaxation mechanism. The obtained results that the dielectrical parameters of the HAp sample can be controlled by EDTA. Ó 2014 Elsevier B.V. All rights reserved.
Hydroxyapatite (HAp), which is a member of the calcium phosphate family, is one of the most known biomaterials, and its chemical formula is Ca10(PO4)6(OH)2 [1–3]. The crystal structure of HAp is hexagonal and its lattice parameters are a = b = 0.9418 nm and ⇑ Corresponding author. Tel.: +90 424 2370000x3623; fax: +90 424 2330062.
http://dx.doi.org/10.1016/j.saa.2014.03.082 1386-1425/Ó 2014 Elsevier B.V. All rights reserved.
20
a b s t r a c t
Introduction
E-mail address: okaygili@firat.edu.tr (O. Kaygili).
32
E3 0.0010
0.0005
a r t i c l e
30
E1
5
0.0015
28
D (nm)
6
E1
E3
E2 20
32
D (nm)
0.0020
σac (S m )
parameters of a and c. The average crystallite size is gradually decreased from 30 to 22 nm. The crystallinity is in the range of 65–71%. Ca/P ratio is higher than the value of 1.67 for EDTA-containing samples.
εο− ε∞
h i g h l i g h t s
c = 0.6884 nm [4,5]. The compositional similarity of HAp with the hard tissues of vertebrates such as bone and teeth makes it very attractive in dental and medical applications as an implant material [6,7]. HAp has a number of excellent properties, including non-toxicity, non-inflammatory, high bioactivity, biocompatibility, osteoconductivity, bone-bonding, chemical stability, resistance to corrosion, low electrical and thermal conductivity, as well as low cost of production [8,9]. On the other hand, HAp has poor mechanical properties in comparison to human bones. Because of this
269
Materials and methods For the synthesis of HAp samples, 0.5 M Ca(NO3)24H2O and 0.3 M (NH4)2HPO4 were separately dissolved in 100 ml of distilled water in two beakers. These solutions were mixed together and were stirred using a magnetic stirrer. 0.01 M EDTA solution in the different amounts (0, 2, 10 and 40 ml) was added to this solution and these samples were named as E0, E1, E2 and E3, respectively. Then, pH of the solution was adjusted to 10 by adding NH4OH. The final solutions were vigorously mixed at 85 °C for 6 h until the beginning of gelation. The obtained gels were kept at 120 °C during 2 h in a furnace and then, the temperature was increased to 180 °C and the obtained gels were dried for 2 h and were heated at 700 °C for 2 h. The crystal structure and the phase analysis of the samples were carried out using X-ray diffraction (XRD) instrument (Bruker D8 Advance). Fourier transform infrared (FTIR) spectra of the samples were recorded by PerkinElmer Spectrum One spectrophotometer. The structural properties of the samples were investigated using a scanning electron microscope (SEM, LEO EVO 40). The dielectric properties were studied using a HIOKI 3532-50 LCR meter at room temperature.
200 150 100 50 0 200 150 100 50 0 200 150 100 50 0 200 150 100 50 0
E2
25
(112)
30
45
(213) (321) (410) (402) (004)
(222)
(312)
(113)
40
(203)
(310)
35
(311)
(202)
(300)
E0
(301)
(102) (210)
(002)
(211)
E1
20
50
55
o
2θ ( ) Fig. 1. XRD patterns of the as-prepared samples.
size is due to the increasing amount of EDTA, because the amount EDTA increases the dissolution rate of Ca(NO3)24H2O and (NH4)2HPO4 precursors in the distilled water during the formation of gels. The dissolution rate changes the size of nucleolus during the nucleation stage of the particles and in turn, the particle size is decreased with EDTA amount. The obtained average crystallite size values suggest that all the samples have the nanostructure. The nanosize is controlled with addition of EDTA into the HAp. The crystallinity (XC) of HAp samples was calculated according to Landi et al. [27]. The crystallinity values of the samples are found to be 70%, 71%, 65% and 65% for E0, E1, E2 and E3, respectively. The crystallinity of pure-HAp is very close to that of the calculated value for HAp (75%) by Qian et al. [28] and it is changed with the addition of EDTA into HAp. The lattice parameters (a and c) and volume of the unit cell (V) of the HAp samples were determined by the following relations [29]: Table 1 The calculated values of the lattice parameters and the volume of the unit cell. Sample
a (nm)
c (nm)
V (nm3)
E0 E1 E2 E3
0.9373 0.9434 0.9384 0.9373
0.6833 0.6890 0.6864 0.6838
0.5199 0.5310 0.5234 0.5202
60 30
Results and discussion
E3
0 60
Transmittance (%)
XRD patterns of the samples are shown in Fig. 1. All the diffraction peaks agree with the hexagonal HAp (JCPDS No: 09-432). The secondary phases of b-TCP (tricalcium phosphate) and CaO were not observed in the XRD patterns, and this result confirms that EDTA-assisted HAp samples are pure materials. The narrow peaks in the XRD patterns indicate the high crystalline structure. Additionally, the XRD patterns show that all the samples compose of the randomly oriented crystals. Scherrer relation was used to calculate average crystallite size, D, of the samples [26]. (0 0 2) and (2 1 1) planes were chosen for calculating the average crystallite size and the obtained values are 29.45, 26.82, 26.14 and 22.23 nm for E0, E1, E2 and E3, respectively. With the addition of EDTA into the HAp, the average crystallite size decreases from 30 to 22 nm. The decrease in the particle
E3
(200) (111)
drawback, the clinical use of HAp as a load-bearing implant is limited [10]. The preparation of HAp has been employed by several methods, including hydrothermal, solid-state reaction, spray pyrolysis and sol–gel techniques [11–17]. In comparison to the other methods; sol–gel offers some advantages, including easily preparation, high purity, nanostructure and low synthesis temperatures [18–20]. Ethylenediamine tetraacetic acid (EDTA), which is a very important and well-known analytical reagent, has been used as the chelating agent that influences cell–cell contacts regulated by Ca2+ ions. EDTA is also used to control the nucleation and growth mechanisms of HAp crystals [21–23]. Although the effects of EDTA on the as-mentioned above properties of HAp were investigated, there was no article related to the detailed study of the electrical and dielectric properties of EDTA-assisted HAp samples. Of course, one of the most desired properties for a material, which can be used for bone application, is to have the same electrical and dielectric properties like bone since these properties are more important for bone healing applications [24,25]. Thus, in order to control the dielectric properties of the HAP, we synthesized the hydroxyapatite (HAp) in the presence of various molar concentration of ethylenediamine tetraacetic acid to control the crystallize size, crystallization and dielectric parameters. The structural, crystallinity and dielectrical properties of HAp samples were investigated and the obtained results were analyzed in detail.
Intensity (Counts)
O. Kaygili et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 268–273
E2
30 0 60 30
E1
0 60
E0
30 0 4000 3600 3200 2800 2400 2000 1600 1200
Wavenumber (cm−1) Fig. 2. FTIR spectra of all the samples.
800
400
270
O. Kaygili et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 268–273
Fig. 3. SEM images and EDX spectrum of pure-HAp and EDTA-assisted HAp samples.
1 2
d
2
¼
2
2
4ðh þ hk þ k Þ l þ 2 3a2 c
V ¼ 0:866a2 c
ð1Þ ð2Þ
where d is the distance for two adjacent planes, and h, k and l are the Miller indices. The calculated values of a, c and V of the samples are given in Table 1. By the adding EDTA, both lattice parameters and volume of the unit cell are gradually decreased for EDTA assisted HAp samples. The FTIR spectra of all the samples are shown in Fig. 2. The bands at 566, 601, 962, 1034 and 1090 cm1 are associated to
the bending and stretching modes of the phosphate groups. The bands at 632 and 3571 cm1 are attributed to the bending and stretching modes of the hydroxyl group [30,31]. The bands at 1637 and 3445 cm1 are assigned to the adsorbed water. In the spectra obtained by FTIR analyses, the phosphate peaks became sharper and split in the range of 566–1090 cm1 [32,33]. These findings confirm the high crystallinity and support the XRD results. Fig. 3 shows the SEM images and energy dispersive X-ray (EDX) analysis results of all the HAp samples. SEM images show the different morphologies and there is a distribution of small particles and large agglomerates. Ca, P and O were detected by EDX analysis and this result confirms that all the samples did not include any
271
O. Kaygili et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 268–273 3.5
impurity. The Ca/P ratios for the samples were found to be 1.71, 2.18, 2.18 and 2.13 for E0, E1, E2 and E3, respectively. The Ca/P ratio (1.71) of E0 sample is close to the stoichiometric ratio for HAp (1.67). The Ca/P ratio increases with the addition of EDTA. This result can be explained as follows. Some chemicals such as EDTA and citric acid have the altering effects on the chemical structure of dentine [34,35]. It is an expected result that the amount of EDTA affects evidently the chemical composition of HAp since HAp has similar composition of bones and teeth [6,7]. The relative permittivity (e0 ), dielectric loss (e00 ) and alternating current conductivity (rac) values of the samples were calculated by the following relations [36,37]:
Cl
ε"
2.0
e00 ¼ tan d e0
0.5 0.0 2.0M
ð5Þ
where eo is the permittivity of free space, A is the area of the electrode and C and l are the capacitance and thickness of the sample, respectively. tan d is the loss tangent and Z is the impedance of the sample. The plots of the relative permittivity vs. frequency are shown in Fig. 4. The e0 values of the samples at 1 kHz are found to be 12.78, 15.77, 10.32 and 14.34 for E0, E1, E2 and E3, respectively, and are in good agreement with the reported values in the literature for the synthetic hydroxyapatites and different bone species [38–41]. The amount of EDTA significantly affects the relative permittivity. The change in the relative permittivity values is due to the ionic polarization [42]. The EDTA changes the ionic polarization of the HAp sample and in turn, the dipole moment of the HAp sample is changed with the EDTA contents. Thus, the change in dipole moment causes a change in the relative permittivity. The relative permittivity (e0 ) values of the samples indicate a non-linear variation with EDTA content. This non-linear variation of relative permittivity with EDTA content is resulted from the particles sizes of the samples. The change in dielectric parameters of the HAp sample in the presence of EDTA can be attributed to the nanosize of the particles. The nanosize particles change ionic polarization of the HAp and thus, relative permittivity is changed. The plots of the dielectric loss as a function of frequency are shown in Fig. 5. As seen in Fig. 5, the e00 values are changed with adding of EDTA. The dielectric loss plots exhibits a relaxation peak and its position did not shift with EDTA amount. This suggests that the relaxation time did not significantly change with EDTA content, but, the dielectric constants are changed. The relaxation peak indicates the presence of a dielectric relaxation mechanism in the samples. In order to analyze the
2.5M
3.0M
3.5M
4.0M
4.5M
5.0M
f (Hz) Fig. 5. Plots of the dielectric loss as a function of frequency.
ð4Þ
l ZA
1.5 1.0
ð3Þ
eo A
rac ¼
2.5
dielectric relaxation mechanism of the samples, we used the following Cole–Cole relation [43,44]:
e e1 ¼
eo e1 1a 1 þ ðixso Þ
ð6Þ
where e* is the complex dielectric constant, eo and e1 are the ‘‘static’’ and ‘‘infinite frequency or optical’’ dielectric constants, so is the relaxation time and a is an exponent (0 < a < 1). The Cole–Cole plots of the samples are shown in Fig. 6. The values of the e1, eo, eo e1 (De, known as the dielectric strength), a and so parameters were calculated and are given in Table 2. The a value is changed with EDTA amount. As seen in Fig. 6, when a increases, the semi-circle is depressed [45]. The so values for EDTA assisted samples are a slightly lower than that of the pure-HAp. The obtained a values suggest that the samples exhibited a non-Debye relaxation mechanism. In this mechanism, electric dipole is interacted with each other and they have the same constant time. The diameter of Cole–Cole curves of the samples is changed with EDTA content. This means that the electric dipoles are interacted with each other and this causes a change in the dielectric dipole moment and in turn, the relative
3.0
E0 E1 E2 E3
2.5
ε"
e0 ¼
E0 E1 E2 E3
3.0
2.0
1.5
20
E0 E1 E2 E3
16
1.0 10
11
12
13
14
15
16
17
18
19
20
ε'
ε'
Fig. 6. Cole–Cole plots of the samples. 12
Table 2 The calculated values of the e1, eo, eo e1, a and so. 8 2.0M
2.5M
3.0M
3.5M
4.0M
4.5M
5.0M
f (Hz) Fig. 4. Relative permittivity vs. frequency plots of the as-synthesized samples.
Sample
e1
eo
eo e1
a
so (ns)
E0 E1 E2 E3
11.45 15.13 9.91 13.93
14.79 19.67 12.61 17.95
3.34 4.54 2.70 4.02
0.033 0.057 0.020 0.036
34.62 34.58 34.54 34.54
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O. Kaygili et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 268–273 20
1.0
1 kHz 2 MHz
18
E3
E1
0.6
14
ε"
ε'
16
E3
0.8
E1
1 kHz 2 MHz
E0
0.4 12 0.2
E0
10
E2 20
22
24
E2
0.0
8 26
28
30
20
32
22
24
D (nm) -3
30
32
6
E1
E3
28
D (nm)
2.0x10
-3
26
1 kHz 2 MHz
E1
5
1.5x10
-3
1.0x10
ε ο− ε ∞
σac (S/m)
E3
-4
5.0x10
4
3
E0 E2
2 0.0
E0
E2
1 20
22
24
26
28
30
32
20
D (nm)
22
24
26
28
30
32
D (nm)
Fig. 7. Calculated values of the relative permittivity, dielectric loss, alternating current conductivity and dielectric strength at 1 kHz and 2 MHz as a function of the crystallite size.
6x10
E0 E1 E2 E3
5x10 -3
σac (S/m)
where rdc is the direct current conductivity, B is a constant, x is the angular frequency and s is an exponent. The s values calculated from the slope of log rac vs. log x plot were found to be 1.003, 1.004, 1.003 and 1.003 for E0, E1, E2 and E3, respectively. All the s values are higher slightly than 1. This suggests that alternating current conductivity mechanism of the samples is taken place with hopping process conduction mechanism [47,48]. Also, the samples exhibited a non-Debye relaxation mechanism and this confirms that the movement of charge carriers is occurred via hopping process among localized states [49].
-3
4x10 -3
3x10 -3
2x10 -3
1x10
Conclusions
-3
2.0M
2.5M
3.0M
3.5M
4.0M
4.5M
5.0M
f (Hz) Fig. 8. Plots of the alternating current conductivity vs. frequency.
permittivity and dielectric loss values of the samples are changed. As can be seen from Fig. 7, the values of the relative permittivity, dielectric loss, alternating current conductivity and dielectric strength are closely related with the crystallite size. The relaxation strengths (De) values of the samples are changed non-monotonously with EDTA content. The change in De values is due to the change in effective dipole moment. As can be seen from Fig. 8, the rac values increase with increasing frequency. The determination of the conductivity mechanism of the samples was carried out using the well known Jonscher relation [46]
rac ¼ rdc þ Bxs
ð7Þ
EDTA assisted HAp samples without any impurities were successfully prepared by sol–gel method. The lattice parameters (a and c) and volume (V) of the unit cell values are gradually decreased by the addition of EDTA, as well as the average crystallite size. The microstructure of HAp sample was changed with the presence of EDTA in apatitic structure. For EDTA-containing samples, Ca/P ratio is higher than that of the standard value of HAp (1.67). By the adding EDTA, the values of the relative permittivity, dielectric loss and alternating current conductivity are significantly changed. The rac values increase with increasing frequency and obey the universal power law behavior. Additionally, the relaxation time and dielectric strength are affected by the amount of EDTA, as well as the parameters of e1 and eo. The obtained results indicate that the addition of EDTA affects all the above-mentioned parameters. The crystallite size, both lattice parameters, volume of the unit cell and dielectric properties can be easily controlled by the helping of analytical EDTA reagent.
O. Kaygili et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 129 (2014) 268–273
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