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molten salt method
Author's Accepted Manuscript
Structural, magnetic and electromagnetic properties of plate-like Zn2W barium hexagonal ferrites prepared by coprecipitation/molten salt method Guoyu Wang, Yongbao Feng, Tai Qiu, Jingfeng Xu, Sainan Chen
www.elsevier.com/locate/ceramint
PII: DOI: Reference:
S0272-8842(15)01314-0 http://dx.doi.org/10.1016/j.ceramint.2015.07.028 CERI10912
To appear in:
Ceramics International
Received date: Revised date: Accepted date:
3 June 2015 3 July 2015 5 July 2015
Cite this article as: Guoyu Wang, Yongbao Feng, Tai Qiu, Jingfeng Xu, Sainan Chen, Structural, magnetic and electromagnetic properties of plate-like Zn2W barium hexagonal ferrites prepared by coprecipitation/molten salt method, Ceramics International, http: //dx.doi.org/10.1016/j.ceramint.2015.07.028 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Structural, magnetic and electromagnetic properties of plate-like Zn2W barium hexagonal ferrites prepared by coprecipitation/molten salt method Guoyu Wanga, Yongbao Fenga,b,∗, Tai Qiua, Jingfeng Xua, Sainan Chena a
College of Materials Science and Engineering, Nanjing Tech University, No. 5 Xinmofan Road, Nanjing 210009, China
b
Nanjing Sanle Electronic Information Industry Group Co. Ltd., No. 5 Guangming Road, Nanjing Pukou Economic Development Zone, 211800, China
Abstract Plate-like Zn2W barium hexagonal ferrites were prepared using a combined coprecipitation and molten salt method. The thermal decomposition behavior of precipitates was systematically studied by TG-DSC and XRD. Pure plate-like Zn2W barium hexagonal ferrites with optimal properties were obtained at a synthesis temperature of 1150 °C for 1 h. Phase composition, morphology and magnetic properties of the Zn2W ferrite powders synthesized at different temperatures (1100 °C–1250 °C) and different holding times (0.5–3 h) were investigated by XRD, SEM and VSM. The electromagnetic parameters were studied by VNA. Saturation magnetization of Zn2W ferrite synthesized at 1150 °C for 1 h reached the maximum of 76.24 emu/g, whereas coercivity decreased with the increase in synthesis temperature and holding time. Keywords: Barium hexagonal ferrite; Coprecipitation; Molten salt method; Thermal
∗
Corresponding author: Address: College of Materials Science and Engineering, Nanjing Tech University, No. 5 Xinmofan Road, Nanjing 210009, China (Y. B. Feng). Tel: +86 25 83587262. Fax: +86 25 83587268. E-mail addresses: [email protected] (Y. B. Feng). 1
decomposition behavior; Plate-like shape; Saturation magnetization 1. Introduction With the rapid development of modern communication and use of electronic devices, electromagnetic and microwave radiation are becoming a real threat to human health. Hence, anti-radiation and microwave absorbing materials are attracting increasing attention from scientists and researchers [1–3]. W-type hexagonal ferrites are excellent microwave absorbing materials because of their plate-like shapes and strong magnetic losses [4,5]. The synthesis of W-type hexagonal ferrites is receiving extensive interest. To date, a number of synthetic methods have been used to prepare W-type hexagonal ferrites. These methods include standard ceramic method, coprecipitation, sol-gel autocombustion and glass crystallization. Ashima et al. [6] prepared Ba(Zn0.5Cd0.5)2Fe16O27 hexagonal ferrites at 1300 °C for 4 h by standard ceramic method. Saturation magnetization and coercivity values are 50.48 emu/g and 1.2 kOe, respectively.
Wang
et
al.
[7]
used
coprecipitation
to
synthesize
Ba(MnZn)0.3Co1.4Re0.01Fe15.99O27 (Re = Dy, Nd and Pr) hexagonal ferrites at 1260 °C for 2.5 h. They focused on the influence of rare earth elements on microwave absorbing properties. Mukhtar et al. [4] synthesized Ba0.5Sr0.5Co1.5Me0.5Fe16O27 (Me = Mn, Mg, Zn and Ni) hexagonal ferrites at 1300 °C for 5 h using sol-gel autocombustion. In their research, thermal decomposition behavior of precipitates was carried out via differential thermal/thermogravimetric analysis. Surig et al. [8] successfully prepared polycrystalline powder samples of W-type BaZn2-xCoxFe16O27 2
hexagonal ferrites by glass crystallization at 1100 °C. A glass consisting of 30.7 BaO, 24.3 B2O3, 35.82 Fe2O3 and 9.28 CoO+ZnO (mol%) was melted at 1400 °C. Generally, raw materials can be mixed at the ionic level using coprecipitation. Using the molten salt method, NaCl and/or KCl are added to raw materials and then heated to a state of flux, allowing solid melts to react much faster because of the small diffusion distances and higher mobility of oxides in the melt [9]. In recent years, the molten salt method has been used to synthesize spinel ferrites [10–12] and M-type hexagonal ferrites [13–15]. However, to date, only a few reports on the synthesis of W-type hexagonal ferrites by the molten salt method exist [16,17]. The present paper presents a novel method that combines coprecipitation with the molten salt method to synthesize plate-like Zn2W barium hexagonal ferrites. This work aimed to study the thermal decomposition behavior of the precipitates and investigate the influence of synthesis temperature and holding time on the phase, microstructural and magnetic properties. 2. Experimental To synthesize Zn2W barium hexagonal ferrites, analytical grade BaCl2·2H2O (99.5%), ZnCl2 (98%), FeCl3·6H2O (98%), NaOH (96%), Na2CO3 (99.8%), CH3CH2OH (99.7%), KCl (99.5%) and NaCl (99.5%) were used. During chemical coprecipitation, stoichiometric amounts of BaCl2·2H2O, ZnCl2 and FeCl3·6H2O were dissolved in distilled deionized water to form a homogeneous solution under constant mechanical stirring. A mixture of NaOH and Na2CO3 in a molar ratio of 5:1 was then slowly added to increase the pH to 10. After 1 h of 3
vigorous stirring, the coprecipitated solutions were filtered, repeatedly washed with distilled deionized water until the solution became neutral and dried at 100 °C for 8 h. The dried precipitates, NaCl and KCl were weight in a mass ratio of 10:3:3, and milled to powder mixtures. The powder mixtures were calcined at different temperatures and holding times in a temperature programmed tube furnace at a heating rate of 5 °C/min under air atmosphere. Subsequently, the calcined products were washed five times with deionized water to remove NaCl and KCl. Zn2W ferrite powders were obtained after dried. For electromagnetic parameters measurement, Zn2W ferrite powder was first pressed into a disk-shaped specimen, and sintered at 1400 °C for 2 h. The Zn2W ferrite disk was then machined to ring shape with an outer diameter of 7 mm, inner diameter of 3.04 mm, and thickness of 2.5 mm. The thermal decomposition behavior of precipitates was investigated by thermogravimetry and differential scanning calorimetry (TG-DSC,
Netzsch
STA449F1) under air atmosphere. Phase identification was conducted via step-scanning X-ray diffraction (XRD, Rigaku SmartLab) using Cu Kα radiation. The hysteresis loops were detected using a vibrating sample magnetometer (VSM, Lakeshore 7303). The morphology of the samples was observed by scanning electron microscopy (SEM, Hitachi TM3000). The electromagnetic parameters and scattering parameter (S11) were measured using a vector network analyzer (VNA, Agilent E5071C).
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3. Results and discussion 3.1 Characterization of precipitates To confirm the phase composition of the precipitates, BaCO3, Zn(OH)2 and Fe(OH)3 were prepared. The XRD patterns of the precipitates, BaCO3, Zn(OH)2 and Fe(OH)3 are shown in Fig. 1. From the patterns of precipitates, only peaks of BaCO3 and Zn(OH)2 were detected (identified by standard PDF card no. 05-0378 and no. 48-1066), thereby confirming the formation of crystalline BaCO3 and Zn(OH)2. However, no evident peak appeared in the XRD pattern of Fe(OH)3 as the precipitates of Fe3+ are amorphous. The TG-DSC curves of the precipitates, BaCO3, Zn(OH)2 and Fe(OH)3 are shown in Figs. 2(a)–(d), respectively. To systematically analyze the thermal decomposition behavior of the precipitates, a small amount of precipitates was sintered at 500 °C, 700°C, 800 °C, 1000 °C and 1100 °C. The XRD patterns of the products are shown in Fig. 3. As shown in Fig. 2(a), the first weight loss of 4% with a corresponding peak in the DSC curve (92 °C) was due to the evaporation of adsorbed water. The following weight loss of 10.4% from 92 °C to 500 °C without evident endothermic or exothermic peaks was attributed to the slow decomposition of Zn(OH)2 and Fe(OH)3, which could be confirmed by Figs. 2(c), 2(d) and 3. With the increase in temperature, two endothermic peaks appeared (Fig. 2(b)), which could be ascribed to the phase transition of BaCO3 [18]. The endothermic peak at 1135 °C accompanied with weight loss showed the decomposition of BaCO3. However, the 5
final weight loss of 3.6% with a broader exothermic platform in Fig. 2(a) compared with that in Fig. 2(d) was attributed to the slow formation of BaFe12O19, which could be found in the XRD patterns in Fig. 3. Thus, barium carbonate could set off a chemical reaction with ferric oxide below the decomposition temperature of BaCO3. 3.2 Effects of synthesis temperature on the phase composition, morphology and magnetic properties of Zn2W ferrites 3.2.1 Phase analysis The XRD patterns of Zn2W ferrite powders synthesized at 1100 °C, 1150 °C, 1200 °C and 1250 °C for 2 h are shown in Fig. 4. From the pattern of the powder synthesized at 1100 °C, five extra peaks associated with the M-type hexagonal ferrite crystal structure were detected. The appearance of the impurity phase was due to the low synthesis temperature, so the synthesis temperature was increased to 1150 °C, 1200 °C and 1250 °C. XRD results showed that the powders were single phase with well-defined Zn2W barium hexagonal ferrites (identified by standard PDF card no. 52-1868), without evident intermediate phase. 3.2.2 Morphology The SEM images of Zn2W ferrite powders synthesized at different temperatures are shown in Fig. 5. As illustrated in Fig. 5(a), many small irregular particles were observed because of the impurities in the powder synthesized at 1100 °C. Other powders synthesized at 1150 °C, 1200 °C and 1250 °C all presented hexagonal plate-like shapes. Furthermore, when the temperature was increased to 1250 °C, the size of some particles significantly increased. 6
3.2.3 Magnetic properties The hysteresis loops of Zn2W ferrite powders synthesized at different temperatures are shown in Fig. 6, whereas Fig. 7 shows the variation in saturation magnetization (Ms), remanent magnetization (Mr) and coercivity (Hc) of Zn2W ferrite powders synthesized at different temperatures. The results indicated that the value of Ms increased and then decreased with the increase in synthesis temperature, with a maximum of 75.14 emu/g at 1200 °C. The values of Mr and Hc decreased with increasing synthesis temperature. The maximum value of Hc (549 Oe) was observed for the sample synthesized at 1100 °C and this high value was attributed to the presence of BaFe12O19. The Hc value of M-type hexagonal ferrites can reach up to thousands of Oersted [19,20]. A decrease in the coercivity with increasing synthesis temperature could be attributed to the elimination of impurities, improvement of phase quality and increase in particle size. This phenomenon could also be ascribed to the transition from magnetic single domain to magnetic multi-domain structure during the increase in particle size with the increase in synthesis temperature [21,22]. 3.3 Effects of holding time on phase composition, morphology and magnetic properties of Zn2W ferrites 3.3.1 Phase analysis The XRD patterns of Zn2W ferrite powders synthesized at 1150 °C for 0.5, 1, 2 and 3 h are shown in Fig. 8. The patterns confirmed that all samples exhibited a well-defined hexagonal W-type phase, except the sample synthesized at 1150 °C for 0.5 h. Three impurity peaks were observed in the pattern of the sample synthesized at 7
1150 °C for 0.5 h because of the existence of M-type hexagonal ferrites. Hence, using the combined coprecipitation/molten salt method to prepare BaZn2Fe16O27 hexagonal ferrites could reduce the synthesis temperature and holding time compared with other methods [23,24]. 3.3.2 Morphology The SEM images of Zn2W ferrite powders synthesized at different holding times are shown in Fig. 9. Some small irregular particles caused by the existence of M-type hexagonal ferrites are shown in Fig. 9(a). Hexagonal plate-like shapes were presented in Figs. 9(b)–(d). The size of particles at a holding time of 3 h slightly increased. 3.3.3 Magnetic properties The hysteresis loops of Zn2W ferrite powders synthesized at 1150 °C at different holding times are shown in Fig. 10. The variations in Ms, Mr and Hc with increasing holding time are presented in Fig. 11. Ms initially increased to 76.24 emu/g and then decreased with increasing holding time. Ms of samples synthesized at 1150 °C for 1 h was higher than that from an earlier report [23] for W-type hexagonal ferrites with formula BaZn2Fe16O27. 3.4 Electromagnetic parameters and reflection loss The Zn2W ferrite powder synthesized at 1150 °C for 1 h was pressed into a small disk with a diameter of 13 mm and a thickness of 5 mm and sintered at 1400 °C for 2 h, and then the ferrite disk was machined to ring shape for measurement. The real part (ε′) and imaginary part (ε″) of complex permittivity in the frequency range of 100 MHz–4.5 GHz are shown in Fig. 12. ε′ and ε″ decreased from 13.17 to 10.63 and 8
from 3.40 to 0.56, respectively. The real part (µ′)and imaginary part (µ″) of complex permeability are shown in Fig. 13. Based on the figure, µ′ decreased with the increase in frequency and reached a constant of 1.16 in the frequency range of 1–4.5 GHz. Moreover, µ″ decreased when the frequency was less than 200 MHz and then increased when the frequency was more than 200 MHz and less than 360 MHz. Subsequently, µ″ decreased as the frequency exceeded 360 MHz. The dielectric loss (tan δε = ε″/ε′) and magnetic loss (tan δµ = µ″/µ′) of ring-shaped Zn2W ferrite are shown in Fig. 14. The dielectric loss gradually decreased from 0.26 to 0.05 with increasing frequency. Meanwhile, magnetic loss displayed the same variation as µ″, with tan δµ reaching a maximum of 0.66 at 660 MHz. The natural resonance may lead to the spectra of magnetic loss [25]. In a two port network, scattering parameter S11 is equivalent to the input complex reflection coefficient or impedance of the piece of equipment under test [26]. The scattering parameter S11 of ring-shaped Zn2W ferrite was measured by VNA and shown in Fig. 15. From the figure, S11 increased from -32 dB to -5 dB with increasing frequency. And S11 was less than -10 dB when the frequency was between 100 MHz and 1.56 GHz. The impedance matching property of Zn2W ferrite was good in low frequency band. 4 Conclusions The thermal decomposition behavior of the precipitates was systematically studied. Zn2W barium hexagonal ferrites with hexagonal plate-like shape were successfully prepared using a combined coprecipitation/molten salt method. The 9
synthesis temperature and holding time were reduced through this method. Optimal properties of hexagonal ferrites were observed from Zn2W ferrite powder synthesized at 1150 °C for 1 h, with Ms reaching up to 76.24 emu/g. Electromagnetic parameters analysis showed Zn2W barium hexagonal ferrite could be a promising candidate for microwave absorbing materials. Acknowledgements This study was supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions, the Program for Changjiang Scholars and Innovative Research Team in University (PCSIRT, IRT1146) and National Natural Science Foundation of China (No.51307079).
References [1] H. Seyed Hossein, S. Mahsa, Investigation of microwave absorbing properties for magnetic nanofiber of polystyrene polyvinylpyrrolidone, Curr. Appl. Phy. 14 (2014) 928-931. [2] Y. B. Feng, T. Qiu, Enhancement of electromagnetic and microwave absorbing properties of gas atomized Fe-50 wt%Ni alloy by shape, J. Magn. Magn. Mater. 324 (2012) 2528-2533. [3] C. S. Dong, X. Wang, P. H. Zhou, T. Liu, J. L. Xie, L. J. Deng, Microwave magnetic and absorption properties of M-type ferrite BaCoxTixFe12-2xO19 in the Ka band, J. Magn. Magn. Mater. 354 (2014) 340-344. [4] M. Ahmad, I. Ali, R. Grossinger, M. Kriegisch, F. Kubel, M. U. Rana, Effects of divalent ions substitution on the microstructure, magnetic and electromagnetic parameters of Co2W hexagonal ferrites synthesized by sol-gel method, J. Alloys Compd. 579 (2013) 57-64. [5] P. Robert C, Hexagonal ferrites: A review of the synthesis, properties and applications of hexaferrite ceramics, Prog. Mater. Sci. 57 (2012) 1191-1334. [6] H. Ashima, S. Sujata, A. Ashish, D. Reetu, Structural, dielectric and magnetic properties of Cd/Pb doped W-type hexaferrites, J. Magn. Magn. Mater. 349 (2014) 121-127. [7] J. Wang, H. Zhang, S. X. Bai, K. Chen, C. R. Zhang, Microwave absorbing properties of rare-earth elements substituted W-type barium ferrite, J. Magn. Magn. Mater. 312 (2007) 310-313. 10
[8] C. Surig, K. A. Hempel, R. Muller,P. Gornert, Investigations on Zn2-xCoxW-type hexaferrite powders at low temperatures by ferromagnetic resonance, J. Magn. Magn. Mater. 150 (1995) 270-276. [9] X. H. Zhu, J. Zhou, M. C. Jiang, J. Xie, S. Liang, S. Y. Li, Z. D. Liu, Y. Y. Zhu, J. M. Zhu, Z. G. Liu, Molten salt synthesis of bismuth ferrite nano- and microcrystals and their structural characterization, J. Am. Ceram. Soc. 97 (2014) 2223-2231. [10] Y. Q. Tao, Z. Y. Li, Zhou K. C. Zhou, Effects of debinding atmosphere on the microstructure and sintering densification of nickel ferrite, Ceram. Int. 39 (2013) 865-869. [11] S. Darshane, I. S. Mulla, Influence of palladium on gas-sensing performance of magnesium ferrite nanoparticles, Mater. Chem. Phys. 119 (2010) 319-323. [12] M. S. Khandekar, N. L. Tarwal, J. Y. Patil, F. I. Shaikha, I. S. Mullad, S. S. Suryavanshi, Liquefied petroleum gas sensing performance of cerium doped copper ferrite, Ceram. Int. 39 (2013) 5901-5907. [13] E. Aydogan, S. Kaya, A. F. Dericioglu. Morphology and magnetic properties of barium hexaferrite ceramics synthesized in x wt % NaCl-(100-x) wt % KCl molten salts, Ceram. Int. 40 (2014) 2331-2336. [14] H. F. Li, X. Wu, X. W. Luo, Y. Gao, R. Z. Gong, G. He, Molten salt synthesis, magnetic properties and microstructure of CoTi-substituted barium hexaferrites, Rare. Metal. Mat. Eng. 41 (2012) 849-853. [15] S. Dursun, R. Topkaya, N. Akdogan, S. Alkoy, Comparison of the structural and magnetic properties of submicron barium hexaferrite powders prepared by molten salt and solid state calcination routes, Ceram. Int. 38 (2012) 3801-3806. [16] Z. H. Yang, Z. W. Li, Y. H. Yang. Structural and magnetic properties of plate-like W-type barium ferrites synthesized with a combination method of molten salt and sol-gel, Mater. Chem. Phys. 144 (2014) 568-574. [17] H. F. Li, R. Z. Gong, L. R. Fan, X. Wang, X. Shen, Z. K. Feng, Synthesis and properties of Co2W hexaferrites prepared by molten salt method, Rare. Metal. Mat. Eng. 38 (2009) 2053-2056. [18] L. N. Wang, C. D. Xie, J. C. Huo, S. X. Shu, Y. L. Liu, Influence of ethylene diamine tetraacetic acid on the morphology of barium carbonate, J. Syn. Crys. 39 (2010) 788-792. [19] J. Li, H. W. Zhang, Y. X. Li, Q. Li, G. L. Yu, Effect of La-Zn substitution on the structure and magnetic properties of low temperature Co-fired M-Type barium ferrite, J. Supercond. Nov. Magn. 27 (2014) 793-797. [20] H. M. Khan, M. U. Islam, Y. B. Xu, M. A. Iqbal, I. Ali, Structural and magnetic properties of TbZn-substituted calcium barium M-type nano-structured hexa-ferrites, J. Alloys Compd. 589 (2014) 258-262. [21] Z. Mosleh, P. Kameli, M. Ranjbar, H, Salaati, Effect of annealing temperature on structural and magnetic properties of BaFe12O19 hexaferrite nanoparticles, Ceram. Int. 40 (2014) 7279-7284. [22] S. G. Kim, W. N. Wang, T. Iwaki, A. Yabuki, K. Okuama, Low-temperature crystallization of barium ferrite nanoparticles by a sodium citrate-aided synthetic 11
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process, J. Phys. Chem. C. 111 (2007) 10175-10180. D. M. Hemeda, A. Al-Sharif, O. M. Hemeda, Effect of Co substitution on the structural and magnetic properties of Zn-W hexaferrite, J. Magn. Magn. Mater. 315 (2007) L1-L7. H. Yamamoto, K. Suzuki, Properties of anisotropic Ba-Zn-Cu system W-type hexagonal ferrite magnets, Electr. ENn. Jpn. 134 (2001) 36-42. Y. B. Feng, T. Qiu, C. Y. Shen, Absorbing properties and structural design of microwave absorbers based on carbonyl iron and barium ferrite, J. Magn. Magn. Mater. 318 (2007) 8-13. R. Jan, M. B. Khan, Z. M. Khan, Synthesis and electrical characterization of “carbon particles reinforced epoxy-nanocomposite” in Ku-band, Mater. Lett. 70 (2012) 155-159.
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Fig. 1. XRD patterns of the precipitates, BaCO3, Zn(OH)2 and Fe(OH)3.
Fig. 2. TG-DSC curves of the precipitates (a), BaCO3 (b), Zn(OH)2 (c) and Fe(OH)3 (d).
13
Fig. 3. XRD patterns of the products sintered at different temperatures.
Fig. 4. XRD patterns of Zn2W ferrite powders synthesized at different temperatures.
14
Fig. 5. SEM images of Zn2W ferrite powders powde synthesized at 1100 °C (a), 1150 °C (b), 1200 °C (c) and 1250 °C (d).
Fig. 6. Hysteresis ysteresis loops of Zn2W ferrite powders synthesized at different temperatures.
15
Fig. 7. Variation in Ms , Mr and Hc of with increasing synthesis temperatures.
Fig. 8. XRD patterns of Zn2W ferrite powders synthesized at 1150 °C for different holding times.
16
Fig. 9. SEM images of Zn2W ferrite powders powde synthesized at 1150 °C for 0.5 h (a), 1 h (b), 2 h (c) and 3 h (d).
Fig. 10. Hysteresis loops of Zn2W ferrite powders synthesized at 1150 °C for different holding times.
17
Fig. 11. Variation in Ms , Mr and Hc with increasing holding times.
Fig. 12. Complex permittivity of ring-shaped Zn2W ferrite sintered at 1400 °C for 2 h in the frequency range of 100 MHz–4.5 GHz.
18
Fig. 13. Complex permeability of ring-shaped Zn2W ferrite sintered at 1400 °C for 2 h in the frequency range of 100 MHz–4.5 GHz.
Fig. 14. Dielectric loss and magnetic loss of ring-shaped Zn2W ferrite sintered at 1400 °C for 2 h in the frequency range of 100 MHz–4.5 GHz.
19
Fig. 15. Scattering parameter S11 of ring-shaped Zn2W ferrite sintered at 1400 °C for 2 h in the frequency range of 100 MHz–4.5 GHz.
20
Structural, magnetic and electromagnetic properties of plate-like Zn2W barium hexagonal ferrites prepared by coprecipitation/molten salt method Guoyu Wang, Yongbao Feng, Tai Qiu, Jingfeng Xu, Sainan Chen
www.elsevier.com/locate/ceramint
PII: DOI: Reference:
S0272-8842(15)01314-0 http://dx.doi.org/10.1016/j.ceramint.2015.07.028 CERI10912
To appear in:
Ceramics International
Received date: Revised date: Accepted date:
3 June 2015 3 July 2015 5 July 2015
Cite this article as: Guoyu Wang, Yongbao Feng, Tai Qiu, Jingfeng Xu, Sainan Chen, Structural, magnetic and electromagnetic properties of plate-like Zn2W barium hexagonal ferrites prepared by coprecipitation/molten salt method, Ceramics International, http: //dx.doi.org/10.1016/j.ceramint.2015.07.028 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Structural, magnetic and electromagnetic properties of plate-like Zn2W barium hexagonal ferrites prepared by coprecipitation/molten salt method Guoyu Wanga, Yongbao Fenga,b,∗, Tai Qiua, Jingfeng Xua, Sainan Chena a
College of Materials Science and Engineering, Nanjing Tech University, No. 5 Xinmofan Road, Nanjing 210009, China
b
Nanjing Sanle Electronic Information Industry Group Co. Ltd., No. 5 Guangming Road, Nanjing Pukou Economic Development Zone, 211800, China
Abstract Plate-like Zn2W barium hexagonal ferrites were prepared using a combined coprecipitation and molten salt method. The thermal decomposition behavior of precipitates was systematically studied by TG-DSC and XRD. Pure plate-like Zn2W barium hexagonal ferrites with optimal properties were obtained at a synthesis temperature of 1150 °C for 1 h. Phase composition, morphology and magnetic properties of the Zn2W ferrite powders synthesized at different temperatures (1100 °C–1250 °C) and different holding times (0.5–3 h) were investigated by XRD, SEM and VSM. The electromagnetic parameters were studied by VNA. Saturation magnetization of Zn2W ferrite synthesized at 1150 °C for 1 h reached the maximum of 76.24 emu/g, whereas coercivity decreased with the increase in synthesis temperature and holding time. Keywords: Barium hexagonal ferrite; Coprecipitation; Molten salt method; Thermal
∗
Corresponding author: Address: College of Materials Science and Engineering, Nanjing Tech University, No. 5 Xinmofan Road, Nanjing 210009, China (Y. B. Feng). Tel: +86 25 83587262. Fax: +86 25 83587268. E-mail addresses: [email protected] (Y. B. Feng). 1
decomposition behavior; Plate-like shape; Saturation magnetization 1. Introduction With the rapid development of modern communication and use of electronic devices, electromagnetic and microwave radiation are becoming a real threat to human health. Hence, anti-radiation and microwave absorbing materials are attracting increasing attention from scientists and researchers [1–3]. W-type hexagonal ferrites are excellent microwave absorbing materials because of their plate-like shapes and strong magnetic losses [4,5]. The synthesis of W-type hexagonal ferrites is receiving extensive interest. To date, a number of synthetic methods have been used to prepare W-type hexagonal ferrites. These methods include standard ceramic method, coprecipitation, sol-gel autocombustion and glass crystallization. Ashima et al. [6] prepared Ba(Zn0.5Cd0.5)2Fe16O27 hexagonal ferrites at 1300 °C for 4 h by standard ceramic method. Saturation magnetization and coercivity values are 50.48 emu/g and 1.2 kOe, respectively.
Wang
et
al.
[7]
used
coprecipitation
to
synthesize
Ba(MnZn)0.3Co1.4Re0.01Fe15.99O27 (Re = Dy, Nd and Pr) hexagonal ferrites at 1260 °C for 2.5 h. They focused on the influence of rare earth elements on microwave absorbing properties. Mukhtar et al. [4] synthesized Ba0.5Sr0.5Co1.5Me0.5Fe16O27 (Me = Mn, Mg, Zn and Ni) hexagonal ferrites at 1300 °C for 5 h using sol-gel autocombustion. In their research, thermal decomposition behavior of precipitates was carried out via differential thermal/thermogravimetric analysis. Surig et al. [8] successfully prepared polycrystalline powder samples of W-type BaZn2-xCoxFe16O27 2
hexagonal ferrites by glass crystallization at 1100 °C. A glass consisting of 30.7 BaO, 24.3 B2O3, 35.82 Fe2O3 and 9.28 CoO+ZnO (mol%) was melted at 1400 °C. Generally, raw materials can be mixed at the ionic level using coprecipitation. Using the molten salt method, NaCl and/or KCl are added to raw materials and then heated to a state of flux, allowing solid melts to react much faster because of the small diffusion distances and higher mobility of oxides in the melt [9]. In recent years, the molten salt method has been used to synthesize spinel ferrites [10–12] and M-type hexagonal ferrites [13–15]. However, to date, only a few reports on the synthesis of W-type hexagonal ferrites by the molten salt method exist [16,17]. The present paper presents a novel method that combines coprecipitation with the molten salt method to synthesize plate-like Zn2W barium hexagonal ferrites. This work aimed to study the thermal decomposition behavior of the precipitates and investigate the influence of synthesis temperature and holding time on the phase, microstructural and magnetic properties. 2. Experimental To synthesize Zn2W barium hexagonal ferrites, analytical grade BaCl2·2H2O (99.5%), ZnCl2 (98%), FeCl3·6H2O (98%), NaOH (96%), Na2CO3 (99.8%), CH3CH2OH (99.7%), KCl (99.5%) and NaCl (99.5%) were used. During chemical coprecipitation, stoichiometric amounts of BaCl2·2H2O, ZnCl2 and FeCl3·6H2O were dissolved in distilled deionized water to form a homogeneous solution under constant mechanical stirring. A mixture of NaOH and Na2CO3 in a molar ratio of 5:1 was then slowly added to increase the pH to 10. After 1 h of 3
vigorous stirring, the coprecipitated solutions were filtered, repeatedly washed with distilled deionized water until the solution became neutral and dried at 100 °C for 8 h. The dried precipitates, NaCl and KCl were weight in a mass ratio of 10:3:3, and milled to powder mixtures. The powder mixtures were calcined at different temperatures and holding times in a temperature programmed tube furnace at a heating rate of 5 °C/min under air atmosphere. Subsequently, the calcined products were washed five times with deionized water to remove NaCl and KCl. Zn2W ferrite powders were obtained after dried. For electromagnetic parameters measurement, Zn2W ferrite powder was first pressed into a disk-shaped specimen, and sintered at 1400 °C for 2 h. The Zn2W ferrite disk was then machined to ring shape with an outer diameter of 7 mm, inner diameter of 3.04 mm, and thickness of 2.5 mm. The thermal decomposition behavior of precipitates was investigated by thermogravimetry and differential scanning calorimetry (TG-DSC,
Netzsch
STA449F1) under air atmosphere. Phase identification was conducted via step-scanning X-ray diffraction (XRD, Rigaku SmartLab) using Cu Kα radiation. The hysteresis loops were detected using a vibrating sample magnetometer (VSM, Lakeshore 7303). The morphology of the samples was observed by scanning electron microscopy (SEM, Hitachi TM3000). The electromagnetic parameters and scattering parameter (S11) were measured using a vector network analyzer (VNA, Agilent E5071C).
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3. Results and discussion 3.1 Characterization of precipitates To confirm the phase composition of the precipitates, BaCO3, Zn(OH)2 and Fe(OH)3 were prepared. The XRD patterns of the precipitates, BaCO3, Zn(OH)2 and Fe(OH)3 are shown in Fig. 1. From the patterns of precipitates, only peaks of BaCO3 and Zn(OH)2 were detected (identified by standard PDF card no. 05-0378 and no. 48-1066), thereby confirming the formation of crystalline BaCO3 and Zn(OH)2. However, no evident peak appeared in the XRD pattern of Fe(OH)3 as the precipitates of Fe3+ are amorphous. The TG-DSC curves of the precipitates, BaCO3, Zn(OH)2 and Fe(OH)3 are shown in Figs. 2(a)–(d), respectively. To systematically analyze the thermal decomposition behavior of the precipitates, a small amount of precipitates was sintered at 500 °C, 700°C, 800 °C, 1000 °C and 1100 °C. The XRD patterns of the products are shown in Fig. 3. As shown in Fig. 2(a), the first weight loss of 4% with a corresponding peak in the DSC curve (92 °C) was due to the evaporation of adsorbed water. The following weight loss of 10.4% from 92 °C to 500 °C without evident endothermic or exothermic peaks was attributed to the slow decomposition of Zn(OH)2 and Fe(OH)3, which could be confirmed by Figs. 2(c), 2(d) and 3. With the increase in temperature, two endothermic peaks appeared (Fig. 2(b)), which could be ascribed to the phase transition of BaCO3 [18]. The endothermic peak at 1135 °C accompanied with weight loss showed the decomposition of BaCO3. However, the 5
final weight loss of 3.6% with a broader exothermic platform in Fig. 2(a) compared with that in Fig. 2(d) was attributed to the slow formation of BaFe12O19, which could be found in the XRD patterns in Fig. 3. Thus, barium carbonate could set off a chemical reaction with ferric oxide below the decomposition temperature of BaCO3. 3.2 Effects of synthesis temperature on the phase composition, morphology and magnetic properties of Zn2W ferrites 3.2.1 Phase analysis The XRD patterns of Zn2W ferrite powders synthesized at 1100 °C, 1150 °C, 1200 °C and 1250 °C for 2 h are shown in Fig. 4. From the pattern of the powder synthesized at 1100 °C, five extra peaks associated with the M-type hexagonal ferrite crystal structure were detected. The appearance of the impurity phase was due to the low synthesis temperature, so the synthesis temperature was increased to 1150 °C, 1200 °C and 1250 °C. XRD results showed that the powders were single phase with well-defined Zn2W barium hexagonal ferrites (identified by standard PDF card no. 52-1868), without evident intermediate phase. 3.2.2 Morphology The SEM images of Zn2W ferrite powders synthesized at different temperatures are shown in Fig. 5. As illustrated in Fig. 5(a), many small irregular particles were observed because of the impurities in the powder synthesized at 1100 °C. Other powders synthesized at 1150 °C, 1200 °C and 1250 °C all presented hexagonal plate-like shapes. Furthermore, when the temperature was increased to 1250 °C, the size of some particles significantly increased. 6
3.2.3 Magnetic properties The hysteresis loops of Zn2W ferrite powders synthesized at different temperatures are shown in Fig. 6, whereas Fig. 7 shows the variation in saturation magnetization (Ms), remanent magnetization (Mr) and coercivity (Hc) of Zn2W ferrite powders synthesized at different temperatures. The results indicated that the value of Ms increased and then decreased with the increase in synthesis temperature, with a maximum of 75.14 emu/g at 1200 °C. The values of Mr and Hc decreased with increasing synthesis temperature. The maximum value of Hc (549 Oe) was observed for the sample synthesized at 1100 °C and this high value was attributed to the presence of BaFe12O19. The Hc value of M-type hexagonal ferrites can reach up to thousands of Oersted [19,20]. A decrease in the coercivity with increasing synthesis temperature could be attributed to the elimination of impurities, improvement of phase quality and increase in particle size. This phenomenon could also be ascribed to the transition from magnetic single domain to magnetic multi-domain structure during the increase in particle size with the increase in synthesis temperature [21,22]. 3.3 Effects of holding time on phase composition, morphology and magnetic properties of Zn2W ferrites 3.3.1 Phase analysis The XRD patterns of Zn2W ferrite powders synthesized at 1150 °C for 0.5, 1, 2 and 3 h are shown in Fig. 8. The patterns confirmed that all samples exhibited a well-defined hexagonal W-type phase, except the sample synthesized at 1150 °C for 0.5 h. Three impurity peaks were observed in the pattern of the sample synthesized at 7
1150 °C for 0.5 h because of the existence of M-type hexagonal ferrites. Hence, using the combined coprecipitation/molten salt method to prepare BaZn2Fe16O27 hexagonal ferrites could reduce the synthesis temperature and holding time compared with other methods [23,24]. 3.3.2 Morphology The SEM images of Zn2W ferrite powders synthesized at different holding times are shown in Fig. 9. Some small irregular particles caused by the existence of M-type hexagonal ferrites are shown in Fig. 9(a). Hexagonal plate-like shapes were presented in Figs. 9(b)–(d). The size of particles at a holding time of 3 h slightly increased. 3.3.3 Magnetic properties The hysteresis loops of Zn2W ferrite powders synthesized at 1150 °C at different holding times are shown in Fig. 10. The variations in Ms, Mr and Hc with increasing holding time are presented in Fig. 11. Ms initially increased to 76.24 emu/g and then decreased with increasing holding time. Ms of samples synthesized at 1150 °C for 1 h was higher than that from an earlier report [23] for W-type hexagonal ferrites with formula BaZn2Fe16O27. 3.4 Electromagnetic parameters and reflection loss The Zn2W ferrite powder synthesized at 1150 °C for 1 h was pressed into a small disk with a diameter of 13 mm and a thickness of 5 mm and sintered at 1400 °C for 2 h, and then the ferrite disk was machined to ring shape for measurement. The real part (ε′) and imaginary part (ε″) of complex permittivity in the frequency range of 100 MHz–4.5 GHz are shown in Fig. 12. ε′ and ε″ decreased from 13.17 to 10.63 and 8
from 3.40 to 0.56, respectively. The real part (µ′)and imaginary part (µ″) of complex permeability are shown in Fig. 13. Based on the figure, µ′ decreased with the increase in frequency and reached a constant of 1.16 in the frequency range of 1–4.5 GHz. Moreover, µ″ decreased when the frequency was less than 200 MHz and then increased when the frequency was more than 200 MHz and less than 360 MHz. Subsequently, µ″ decreased as the frequency exceeded 360 MHz. The dielectric loss (tan δε = ε″/ε′) and magnetic loss (tan δµ = µ″/µ′) of ring-shaped Zn2W ferrite are shown in Fig. 14. The dielectric loss gradually decreased from 0.26 to 0.05 with increasing frequency. Meanwhile, magnetic loss displayed the same variation as µ″, with tan δµ reaching a maximum of 0.66 at 660 MHz. The natural resonance may lead to the spectra of magnetic loss [25]. In a two port network, scattering parameter S11 is equivalent to the input complex reflection coefficient or impedance of the piece of equipment under test [26]. The scattering parameter S11 of ring-shaped Zn2W ferrite was measured by VNA and shown in Fig. 15. From the figure, S11 increased from -32 dB to -5 dB with increasing frequency. And S11 was less than -10 dB when the frequency was between 100 MHz and 1.56 GHz. The impedance matching property of Zn2W ferrite was good in low frequency band. 4 Conclusions The thermal decomposition behavior of the precipitates was systematically studied. Zn2W barium hexagonal ferrites with hexagonal plate-like shape were successfully prepared using a combined coprecipitation/molten salt method. The 9
synthesis temperature and holding time were reduced through this method. Optimal properties of hexagonal ferrites were observed from Zn2W ferrite powder synthesized at 1150 °C for 1 h, with Ms reaching up to 76.24 emu/g. Electromagnetic parameters analysis showed Zn2W barium hexagonal ferrite could be a promising candidate for microwave absorbing materials. Acknowledgements This study was supported by the Priority Academic Program Development of Jiangsu Higher Education Institutions, the Program for Changjiang Scholars and Innovative Research Team in University (PCSIRT, IRT1146) and National Natural Science Foundation of China (No.51307079).
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Fig. 1. XRD patterns of the precipitates, BaCO3, Zn(OH)2 and Fe(OH)3.
Fig. 2. TG-DSC curves of the precipitates (a), BaCO3 (b), Zn(OH)2 (c) and Fe(OH)3 (d).
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Fig. 3. XRD patterns of the products sintered at different temperatures.
Fig. 4. XRD patterns of Zn2W ferrite powders synthesized at different temperatures.
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Fig. 5. SEM images of Zn2W ferrite powders powde synthesized at 1100 °C (a), 1150 °C (b), 1200 °C (c) and 1250 °C (d).
Fig. 6. Hysteresis ysteresis loops of Zn2W ferrite powders synthesized at different temperatures.
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Fig. 7. Variation in Ms , Mr and Hc of with increasing synthesis temperatures.
Fig. 8. XRD patterns of Zn2W ferrite powders synthesized at 1150 °C for different holding times.
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Fig. 9. SEM images of Zn2W ferrite powders powde synthesized at 1150 °C for 0.5 h (a), 1 h (b), 2 h (c) and 3 h (d).
Fig. 10. Hysteresis loops of Zn2W ferrite powders synthesized at 1150 °C for different holding times.
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Fig. 11. Variation in Ms , Mr and Hc with increasing holding times.
Fig. 12. Complex permittivity of ring-shaped Zn2W ferrite sintered at 1400 °C for 2 h in the frequency range of 100 MHz–4.5 GHz.
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Fig. 13. Complex permeability of ring-shaped Zn2W ferrite sintered at 1400 °C for 2 h in the frequency range of 100 MHz–4.5 GHz.
Fig. 14. Dielectric loss and magnetic loss of ring-shaped Zn2W ferrite sintered at 1400 °C for 2 h in the frequency range of 100 MHz–4.5 GHz.
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Fig. 15. Scattering parameter S11 of ring-shaped Zn2W ferrite sintered at 1400 °C for 2 h in the frequency range of 100 MHz–4.5 GHz.
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