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Significantly enhanced impulse breakdown performances of propylene carbonate modified by TiO2 nano-particles
Chemical Physics Letters 662 (2016) 192–195
Contents lists available at ScienceDirect
Chemical Physics Letters journal homepage: www.elsevier.com/locate/cplett
Research paper
Significantly enhanced impulse breakdown performances of propylene carbonate modified by TiO2 nano-particles Yanpan Hou, Zicheng Zhang ⇑, Jiande Zhang College of Optoelectronic Science and Engineering, National University of Defense Technology, Changsha 410073, China
a r t i c l e
i n f o
Article history: Received 28 June 2016 In final form 14 September 2016 Available online 15 September 2016 Keywords: Propylene carbonate Nano-particles Dielectrics Compact pulsed power sources
a b s t r a c t Nano-fluids with KH550-grafted TiO2 nano-particles homogenously dispersed into propylene carbonate exhibit substantially enhanced dielectric properties compared with the base liquid. Specifically, the breakdown stability of nano-fluids is dramatically improved for a small high-voltage electrode potential increasing rate, which has a potential to increase the reliability of the pulsed power system. On the other hand, the mean breakdown voltage of nano-fluids is more than 30% larger than that of base liquid when the high-voltage electrode potential increasing rate equals to 6 kV/ls, which will lead to a great increase in energy storage density of the pulsed power system. Ó 2016 Published by Elsevier B.V.
1. Introduction
2. Experiments
Modern applications have stimulated intense interest in the pulsed power technology towards high average power and compact structure [1–3]. Polar liquids with large dielectric constants and high dielectric strength are of major importance to the compact pulsed power sources [4]. As a kind of polar liquids, propylene carbonate (PC) has a large relative permittivity, low freezing temperature, high resistivity and low viscosity [5]. Compared with other typical polar liquids, such as deionized water or water/ethylene glycol mixtures, PC has relatively high chemical stability, which can hold the resistivity without decaying for longer periods of time in the pulse forming line. Moreover, Shu et al. [6] in Old Dominion University has demonstrated that PC has higher breakdown strength than that of deionized water. However, despite much previous efforts have been devoted to explore the effective ways to increase the dielectric performances of liquid insulation, such as pressurization and purifying, major improvements are lacking [7–10]. In electrical engineering fields, various favorable results have shown that by adding nanoparticle suspensions into the liquid, the insulating properties of the base liquid can be enhanced [11–13]. Recently, we tried to disperse TiO2 nano-particles into PC and investigated the effect of nano-particles on the pulsed breakdown performance of the base liquid.
2.1. Surface modification of nano-particles and preparation of NFs
⇑ Corresponding author. E-mail address: [email protected] (Z. Zhang). http://dx.doi.org/10.1016/j.cplett.2016.09.043 0009-2614/Ó 2016 Published by Elsevier B.V.
TiO2 nano-particles with average diameter of 30 nm were obtained from Deco Island Gold Ltd. The morphology of nanoparticles was measured by using Scanning Electron Microscope, shown in Fig. 1(a). It reveals apparent agglomeration of nanoparticles due to considerably high surface energy and extremely large surface area/particle size ratio [14]. In order to improve the dispersion ability of nano-particles, caminopropyltriethoxysilane coupling agent (KH550) was used to modify the nano-particle surface and the reaction scheme is illustrated in Fig. 2. Firstly, three AOC2H5 connected to Si were hydrolyzed and then the silanol was generated. After that, the silanol was condensed to be an oligomer. Then the hydrogen bond would be generated by the AOH groups both in the oligomer and on the surface of nano-particles. Finally, through drying or sulfidation processes, the covalent interactions would be formed between the coupling agent and nano-particles. Then, the nano-particles were uniformly dispersed into PC by the ultrasonic dispersion method and agate jar milling technique. Fig. 1(b) shows that the coupling agent KH550 effectively decreases the agglomerations of nano-particles and the size ranges from several nano-meters to several ten nano-meters. In this study, the proportion of nanoparticles in NFs samples was about 0.5 vol%.
Y. Hou et al. / Chemical Physics Letters 662 (2016) 192–195
193
Fig. 1. (a) Scanning Electron Microscope image of outsourcing TiO2 nano-particles and (b) Transmission Electron Microscope image of KH550-grafted TiO2 nano-particles dispersed in PC.
Fig. 2. Reaction scheme for preparing KH550-grafted TiO2 nano-particle.
2.2. Impulse breakdown characteristics of PC and NFs Impulse breakdown voltage and the time lag to breakdown of the liquid samples were measured [15]. The experimental apparatus mainly consists of the primary capacitor, a transformer, the secondary capacitor and the test cell, shown in Fig. 3. The circuit parameters are as follows: the primary capacitance (Cp) is 600 lF and the winding inductance (Lp) is 0.65 lH. In the secondary circuit, the secondary winding inductance (Ls) is 530 mH and the capacitance (Cs) is 1.95 nF. The primary capacitor was charged by commercial power supply and the test cell was in parallel connected to the secondary capacitor. Through changing the voltage applied on the primary capacitor, we could get different highvoltage electrode potential increasing rate, A = 1.5–6 kV/ls. The gap between electrodes was set to be 1 mm during testing. Fig. 3. Impulse breakdown measurement device.
3. Results and discussions Fig. 4(a) shows the examples of measured voltage waveforms across the test gap, which is the mean breakdown voltage among
twenty times of breakdown process for each sample. It is obvious that adding TiO2 nano-particles into PC cannot only enhance the breakdown voltage, but prolong the charge time for each
194
Y. Hou et al. / Chemical Physics Letters 662 (2016) 192–195
Fig. 4. (a) Example of measured waveforms of the voltage across the test gap for various different high-voltage electrode potential increasing rates, and corresponding Weibull plots of breakdown voltage data: (b1) A = 1.5 kV/ls, (b2) A = 3 kV/ls, (b3) A = 6 kV/ls.
high-voltage electrode potential increasing rate. The corresponding Weibull plots of breakdown voltage data is shown in Fig. 4(b1–b3). The gradient of the double logarithmic plot provides a measure of how sensitive the test sample is to an increase in breakdown voltage. Thus, we can get that for A = 1.5 kV/ls, the mean breakdown voltage of NFs is only about 8% larger than that of PC. However, on the other hand, the breakdown stability of NFs is dramatically improved. For A = 3 kV/ls, NFs exhibit nearly 15% larger mean breakdown voltage and slightly higher breakdown stability than those of PC. For A = 6 kV/ls, the mean breakdown voltage of NFs is more than 30% larger than that of PC with nearly the same breakdown stability. PC or PC-based NFs are considered to be used as energy storage media in the pulse forming line. Smaller high-voltage electrode potential increasing rate (A = 1.5–3 kV/ls) in the pulse forming line can easily be gotten under the conditions of available primary source. NFs can be considered as a better candidate than pure PC due to its increased breakdown stability. So the reliability of the pulsed power system can be enhanced. On the other hand, larger high-voltage electrode potential increasing rate (A = 6 kV/ls) of the pulse forming line corresponds to bigger output power, and it is triable to use the medium with greater increments in breakdown voltage. Actually, the maximum energy storage density of a liquid medium is in direct proportion to its permittivity and the square of maximum electric field intensity. That is
wmax ¼
1 2 eE 2
ð1Þ
For NFs containing 0.5 vol% TiO2 nano-particles dispersed into PC, the changes in permittivity can be ignored compared with the base liquid. For A = 6 kV/ls, NFs possess about 30% larger breakdown voltage. In this case, the maximum energy storage density of NFs increases to nearly 1.7 times and the volume of pulse forming line using NFs as energy storage medium can be reduced to 60% compared with that of PC. Through the above analysis, we can get that NFs exhibit the enhanced dielectric properties compared with the base liquid. Possible reason for the experimental results is given below. Interfaces between nano-particles and PC will become increasingly prominent as the nano-particles shrink in size and they have properties different from either the particles or the matrix [16]. There are large quantities of physical and chemical defects in the interfaces, corresponding to myriad trap sites with a range of energies [17,18]. Therefore, charge carriers, which are injected from metallic electrodes under high amplitude electrical stress, can become more trapped in the interfaces. In this way, the energy of the charge carriers in NFs will effectively be reduced and the initiation of breakdown will be inhibited to a great extent. This charge carriers trapping effect of interfaces between nano-particles and PC matrix is considered as the main mechanism leading to the enhanced dielectric performances of PC-based NFs. 4. Conclusions In summary, TiO2 nano-particles modified by KH550 have been homogenously dispersed in PC and the NFs exhibited significantly
Y. Hou et al. / Chemical Physics Letters 662 (2016) 192–195
improved dielectric performance compared with the base liquid. For a small high-voltage electrode potential increasing rate, the addition of nano-particles would lead to greatly improved breakdown stability of base liquid; for a large high-voltage electrode potential increasing rate, NFs exhibited much larger mean breakdown voltage. It is proposed that the interfaces between nanoparticles and PC will create numerous trap sites and capture charge carriers in the matrix. In this way, the energy of the charge carriers in NFs will effectively be reduced. Therefore, in order for charge carriers acquiring enough energy to initiate breakdown in NFs, much higher applied field is needed. Acknowledgments This work was supported by the National Natural Science Foundation of China under Grant No. 51307175. References [1] M. Zahn, Y. Ohki, D.B. Fenneman, R.J. Gripshover, V.H. Gehman, Proc. IEEE 74 (1986) 1182–1221. [2] S.B. Gupta, H. Bluhm, J. Appl. Phys. 101 (2007) 53302.
195
[3] L. Wang, J. Liu, IEEE Trans. Plasma Sci. 43 (2015) 1–7. [4] R.P. Joshi, J. Qian, G. Zhao, J. Kolb, K.H. Schoenbach, E. Schamiloglu, J. Gaudet, J. Appl. Phys. 96 (2004) 5129–5139. [5] R.S. Clark, D.L. Green, M.T. Buttram, R. Lawson, G.J. Rohwein, Studies on the use of propylene carbonate as a high-voltage insulator, in: IEEE Conference Record of the 1988 Eighteenth Power Modulator Symposium, 1988, Hilton Head, SC, 1988, pp. 381–384. [6] X. Shu, J.F. Kolb, M.A. Malik, L. XinPei, M. Laroussi, R.P. Joshi, E. Schamiloglu, K. H. Schoenbach, IEEE Trans. Plasma Sci. 34 (2006) 1653–1661. [7] Z. Zhang, J. Zhang, J. Yang, Plasma Sci. Technol. 7 (2005) 3161–3165. [8] Z. Zhang, J. Zhang, B. Qian, C. Liu, T. Xun, H. Zhang, B. Liang, IEEE Trans. Plasma Sci. 42 (2014) 241–248. [9] Z. Zhang, J. Zhang, H. Yang, B. Qian, Z. Meng, D. Li, Acta Phys. Pol. A 115 (2009) 973–975. [10] Z. Zhang, J. Zhang, J. Yang, Plasma Sci. Technol. 8 (2006) 195–197. [11] J. Lee, W. Kim, Phys. Proc. 32 (2012) 327–334. [12] J. Li, Z. Zhang, P. Zou, S. Grzybowski, M. Zahn, IEEE Electr. Insul. Mag. 28 (2012) 43–50. [13] Y. Du, Y. Lv, C. Li, M. Chen, J. Zhou, X. Li, Y. Zhou, Y. Tu, J. Appl. Phys. 110 (2011) 104104. [14] M. Sabzi, S.M. Mirabedini, J. Zohuriaan-Mehr, M. Atai, Prog. Org. Coat. 65 (2009) 222–228. [15] Y. Hou, Z. Zhang, J. Zhang, Z. Liu, Z. Song, Rev. Sci. Instrum. 86 (2015) 54702. [16] T.J. Lewis, IEEE Trans. Dielect. Electr. Insul. 11 (2004) 739–753. [17] M. Meunier, N. Quirke, A. Aslanides, J. Chem. Phys. 115 (2001) 2876. [18] M. Meunier, N. Quirke, J. Chem. Phys. 113 (2000) 369.
Contents lists available at ScienceDirect
Chemical Physics Letters journal homepage: www.elsevier.com/locate/cplett
Research paper
Significantly enhanced impulse breakdown performances of propylene carbonate modified by TiO2 nano-particles Yanpan Hou, Zicheng Zhang ⇑, Jiande Zhang College of Optoelectronic Science and Engineering, National University of Defense Technology, Changsha 410073, China
a r t i c l e
i n f o
Article history: Received 28 June 2016 In final form 14 September 2016 Available online 15 September 2016 Keywords: Propylene carbonate Nano-particles Dielectrics Compact pulsed power sources
a b s t r a c t Nano-fluids with KH550-grafted TiO2 nano-particles homogenously dispersed into propylene carbonate exhibit substantially enhanced dielectric properties compared with the base liquid. Specifically, the breakdown stability of nano-fluids is dramatically improved for a small high-voltage electrode potential increasing rate, which has a potential to increase the reliability of the pulsed power system. On the other hand, the mean breakdown voltage of nano-fluids is more than 30% larger than that of base liquid when the high-voltage electrode potential increasing rate equals to 6 kV/ls, which will lead to a great increase in energy storage density of the pulsed power system. Ó 2016 Published by Elsevier B.V.
1. Introduction
2. Experiments
Modern applications have stimulated intense interest in the pulsed power technology towards high average power and compact structure [1–3]. Polar liquids with large dielectric constants and high dielectric strength are of major importance to the compact pulsed power sources [4]. As a kind of polar liquids, propylene carbonate (PC) has a large relative permittivity, low freezing temperature, high resistivity and low viscosity [5]. Compared with other typical polar liquids, such as deionized water or water/ethylene glycol mixtures, PC has relatively high chemical stability, which can hold the resistivity without decaying for longer periods of time in the pulse forming line. Moreover, Shu et al. [6] in Old Dominion University has demonstrated that PC has higher breakdown strength than that of deionized water. However, despite much previous efforts have been devoted to explore the effective ways to increase the dielectric performances of liquid insulation, such as pressurization and purifying, major improvements are lacking [7–10]. In electrical engineering fields, various favorable results have shown that by adding nanoparticle suspensions into the liquid, the insulating properties of the base liquid can be enhanced [11–13]. Recently, we tried to disperse TiO2 nano-particles into PC and investigated the effect of nano-particles on the pulsed breakdown performance of the base liquid.
2.1. Surface modification of nano-particles and preparation of NFs
⇑ Corresponding author. E-mail address: [email protected] (Z. Zhang). http://dx.doi.org/10.1016/j.cplett.2016.09.043 0009-2614/Ó 2016 Published by Elsevier B.V.
TiO2 nano-particles with average diameter of 30 nm were obtained from Deco Island Gold Ltd. The morphology of nanoparticles was measured by using Scanning Electron Microscope, shown in Fig. 1(a). It reveals apparent agglomeration of nanoparticles due to considerably high surface energy and extremely large surface area/particle size ratio [14]. In order to improve the dispersion ability of nano-particles, caminopropyltriethoxysilane coupling agent (KH550) was used to modify the nano-particle surface and the reaction scheme is illustrated in Fig. 2. Firstly, three AOC2H5 connected to Si were hydrolyzed and then the silanol was generated. After that, the silanol was condensed to be an oligomer. Then the hydrogen bond would be generated by the AOH groups both in the oligomer and on the surface of nano-particles. Finally, through drying or sulfidation processes, the covalent interactions would be formed between the coupling agent and nano-particles. Then, the nano-particles were uniformly dispersed into PC by the ultrasonic dispersion method and agate jar milling technique. Fig. 1(b) shows that the coupling agent KH550 effectively decreases the agglomerations of nano-particles and the size ranges from several nano-meters to several ten nano-meters. In this study, the proportion of nanoparticles in NFs samples was about 0.5 vol%.
Y. Hou et al. / Chemical Physics Letters 662 (2016) 192–195
193
Fig. 1. (a) Scanning Electron Microscope image of outsourcing TiO2 nano-particles and (b) Transmission Electron Microscope image of KH550-grafted TiO2 nano-particles dispersed in PC.
Fig. 2. Reaction scheme for preparing KH550-grafted TiO2 nano-particle.
2.2. Impulse breakdown characteristics of PC and NFs Impulse breakdown voltage and the time lag to breakdown of the liquid samples were measured [15]. The experimental apparatus mainly consists of the primary capacitor, a transformer, the secondary capacitor and the test cell, shown in Fig. 3. The circuit parameters are as follows: the primary capacitance (Cp) is 600 lF and the winding inductance (Lp) is 0.65 lH. In the secondary circuit, the secondary winding inductance (Ls) is 530 mH and the capacitance (Cs) is 1.95 nF. The primary capacitor was charged by commercial power supply and the test cell was in parallel connected to the secondary capacitor. Through changing the voltage applied on the primary capacitor, we could get different highvoltage electrode potential increasing rate, A = 1.5–6 kV/ls. The gap between electrodes was set to be 1 mm during testing. Fig. 3. Impulse breakdown measurement device.
3. Results and discussions Fig. 4(a) shows the examples of measured voltage waveforms across the test gap, which is the mean breakdown voltage among
twenty times of breakdown process for each sample. It is obvious that adding TiO2 nano-particles into PC cannot only enhance the breakdown voltage, but prolong the charge time for each
194
Y. Hou et al. / Chemical Physics Letters 662 (2016) 192–195
Fig. 4. (a) Example of measured waveforms of the voltage across the test gap for various different high-voltage electrode potential increasing rates, and corresponding Weibull plots of breakdown voltage data: (b1) A = 1.5 kV/ls, (b2) A = 3 kV/ls, (b3) A = 6 kV/ls.
high-voltage electrode potential increasing rate. The corresponding Weibull plots of breakdown voltage data is shown in Fig. 4(b1–b3). The gradient of the double logarithmic plot provides a measure of how sensitive the test sample is to an increase in breakdown voltage. Thus, we can get that for A = 1.5 kV/ls, the mean breakdown voltage of NFs is only about 8% larger than that of PC. However, on the other hand, the breakdown stability of NFs is dramatically improved. For A = 3 kV/ls, NFs exhibit nearly 15% larger mean breakdown voltage and slightly higher breakdown stability than those of PC. For A = 6 kV/ls, the mean breakdown voltage of NFs is more than 30% larger than that of PC with nearly the same breakdown stability. PC or PC-based NFs are considered to be used as energy storage media in the pulse forming line. Smaller high-voltage electrode potential increasing rate (A = 1.5–3 kV/ls) in the pulse forming line can easily be gotten under the conditions of available primary source. NFs can be considered as a better candidate than pure PC due to its increased breakdown stability. So the reliability of the pulsed power system can be enhanced. On the other hand, larger high-voltage electrode potential increasing rate (A = 6 kV/ls) of the pulse forming line corresponds to bigger output power, and it is triable to use the medium with greater increments in breakdown voltage. Actually, the maximum energy storage density of a liquid medium is in direct proportion to its permittivity and the square of maximum electric field intensity. That is
wmax ¼
1 2 eE 2
ð1Þ
For NFs containing 0.5 vol% TiO2 nano-particles dispersed into PC, the changes in permittivity can be ignored compared with the base liquid. For A = 6 kV/ls, NFs possess about 30% larger breakdown voltage. In this case, the maximum energy storage density of NFs increases to nearly 1.7 times and the volume of pulse forming line using NFs as energy storage medium can be reduced to 60% compared with that of PC. Through the above analysis, we can get that NFs exhibit the enhanced dielectric properties compared with the base liquid. Possible reason for the experimental results is given below. Interfaces between nano-particles and PC will become increasingly prominent as the nano-particles shrink in size and they have properties different from either the particles or the matrix [16]. There are large quantities of physical and chemical defects in the interfaces, corresponding to myriad trap sites with a range of energies [17,18]. Therefore, charge carriers, which are injected from metallic electrodes under high amplitude electrical stress, can become more trapped in the interfaces. In this way, the energy of the charge carriers in NFs will effectively be reduced and the initiation of breakdown will be inhibited to a great extent. This charge carriers trapping effect of interfaces between nano-particles and PC matrix is considered as the main mechanism leading to the enhanced dielectric performances of PC-based NFs. 4. Conclusions In summary, TiO2 nano-particles modified by KH550 have been homogenously dispersed in PC and the NFs exhibited significantly
Y. Hou et al. / Chemical Physics Letters 662 (2016) 192–195
improved dielectric performance compared with the base liquid. For a small high-voltage electrode potential increasing rate, the addition of nano-particles would lead to greatly improved breakdown stability of base liquid; for a large high-voltage electrode potential increasing rate, NFs exhibited much larger mean breakdown voltage. It is proposed that the interfaces between nanoparticles and PC will create numerous trap sites and capture charge carriers in the matrix. In this way, the energy of the charge carriers in NFs will effectively be reduced. Therefore, in order for charge carriers acquiring enough energy to initiate breakdown in NFs, much higher applied field is needed. Acknowledgments This work was supported by the National Natural Science Foundation of China under Grant No. 51307175. References [1] M. Zahn, Y. Ohki, D.B. Fenneman, R.J. Gripshover, V.H. Gehman, Proc. IEEE 74 (1986) 1182–1221. [2] S.B. Gupta, H. Bluhm, J. Appl. Phys. 101 (2007) 53302.
195
[3] L. Wang, J. Liu, IEEE Trans. Plasma Sci. 43 (2015) 1–7. [4] R.P. Joshi, J. Qian, G. Zhao, J. Kolb, K.H. Schoenbach, E. Schamiloglu, J. Gaudet, J. Appl. Phys. 96 (2004) 5129–5139. [5] R.S. Clark, D.L. Green, M.T. Buttram, R. Lawson, G.J. Rohwein, Studies on the use of propylene carbonate as a high-voltage insulator, in: IEEE Conference Record of the 1988 Eighteenth Power Modulator Symposium, 1988, Hilton Head, SC, 1988, pp. 381–384. [6] X. Shu, J.F. Kolb, M.A. Malik, L. XinPei, M. Laroussi, R.P. Joshi, E. Schamiloglu, K. H. Schoenbach, IEEE Trans. Plasma Sci. 34 (2006) 1653–1661. [7] Z. Zhang, J. Zhang, J. Yang, Plasma Sci. Technol. 7 (2005) 3161–3165. [8] Z. Zhang, J. Zhang, B. Qian, C. Liu, T. Xun, H. Zhang, B. Liang, IEEE Trans. Plasma Sci. 42 (2014) 241–248. [9] Z. Zhang, J. Zhang, H. Yang, B. Qian, Z. Meng, D. Li, Acta Phys. Pol. A 115 (2009) 973–975. [10] Z. Zhang, J. Zhang, J. Yang, Plasma Sci. Technol. 8 (2006) 195–197. [11] J. Lee, W. Kim, Phys. Proc. 32 (2012) 327–334. [12] J. Li, Z. Zhang, P. Zou, S. Grzybowski, M. Zahn, IEEE Electr. Insul. Mag. 28 (2012) 43–50. [13] Y. Du, Y. Lv, C. Li, M. Chen, J. Zhou, X. Li, Y. Zhou, Y. Tu, J. Appl. Phys. 110 (2011) 104104. [14] M. Sabzi, S.M. Mirabedini, J. Zohuriaan-Mehr, M. Atai, Prog. Org. Coat. 65 (2009) 222–228. [15] Y. Hou, Z. Zhang, J. Zhang, Z. Liu, Z. Song, Rev. Sci. Instrum. 86 (2015) 54702. [16] T.J. Lewis, IEEE Trans. Dielect. Electr. Insul. 11 (2004) 739–753. [17] M. Meunier, N. Quirke, A. Aslanides, J. Chem. Phys. 115 (2001) 2876. [18] M. Meunier, N. Quirke, J. Chem. Phys. 113 (2000) 369.