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Influence of dielectric barrier materials to the behavior of dielectric barrier discharge plasma for CO2 decomposition
Solid State Ionics 172 (2004) 235 – 238 www.elsevier.com/locate/ssi
Influence of dielectric barrier materials to the behavior of dielectric barrier discharge plasma for CO2 decomposition Ruixing Li *, Yukishige Yamaguchi, Shu Yin, Qing Tang, Tsugio Sato Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan Received 9 November 2003; received in revised form 29 January 2004; accepted 26 February 2004
Abstract The aim of this study is to develop an application of dielectric ceramics in a dielectric barrier discharge (DBD) plasma reactor to dissociate CO2 to CO and O2. The fracture strength and dielectric strength of Ca0.7Sr0.3TiO3 were greatly improved by the liquid phase sintering using 0.5 wt.% Li2Si2O5 as a sintering additive. The sintered body was efficient when it was used as a dielectric barrier of a plasma reaction to generate a nonthermal plasma by the DBD. The ratio of CO2 decomposition by the DBD plasma using this Ca0.7Sr0.3TiO3 was much greater than with those using commercial alumina and silica glass barriers. This Ca0.7Sr0.3TiO3 ceramic was sintered using Li2Si2O5 as a sintering additive and used as a dielectric barrier of DBD for the first time. D 2004 Elsevier B.V. All rights reserved. PACS: 34.50.Gb; 34.50.Lf; 52.20.Hv; 52.75.Rx Keywords: Carbon dioxide; Decomposition; Plasma; Dielectric barrier discharge; SrTiO3; CaTiO3
1. Introduction Dielectric barrier discharge (DBD) plasmas are characterized by the presence of one or more insulating layers in the current path between the metal electrode in addition to the discharge gap(s), has been commercially used to produce ozone and has received attention for the application in pollution control, etc. [1– 5]. The dielectric barrier material is one of the key factors for the proper functioning of the DBD plasma [6]. The reactivity of DBD plasma is expected to be improved by increasing the permittivity of the dielectric barrier. However, the use of high dielectric constant ceramics is difficult, since these tend to be fractured when supplying high voltage because of their modest dielectric strength. Therefore, a dielectric barrier with a high dielectric constant and a high dielectric strength is highly desirable in order to generate a DBD plasma possessing high reactivity. It is known that SrTiO3 possesses a high permittivity and a modest dielectric strength. In contrast, CaTiO3 possesses a low dielectric constant and a high dielectric strength. According to the
* Corresponding author. Tel.: +81-22-2175598; fax: +81-22-2175597. E-mail address: [email protected] (R. Li). 0167-2738/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.ssi.2004.02.036
results of Ball [7] and Ceh et al. [8], CaTiO3 and SrTiO3 are completely miscible in forming the solid solution of Ca1 xSrxTiO3 (0 < x V 0.40). Therefore, Ca1 xSrxTiO3 is expected to possess high permittivity, high dielectric strength and to induce the reactive DBD plasma. Many works have been concerned with Ca1 xSrxTiO3 ceramic in the study of its phase transitions [7– 11], but the sintering behavior, dielectric properties and mechanical properties of Ca1 xSrxTiO3 have not been systematically investigated. Recently, it was reported that the sintering temperature of BaTiO3 could be greatly lowered without serious deterioration in the dielectric properties by using Li2Si2O5 [12]. In the present study, Ca0.7Sr0.3TiO3 was sintered using Li2Si2O5 as a sintering aid and used as a barrier material to generate the DBD plasma to decompose CO2 to CO.
2. Experimental procedures Appropriate quantities of CaTiO3, SrTiO3 and Li2Si2O5 were wet-mixed in a polyethylene bottle with ZrO2 balls and ethanol for 16 h and then dried at 85 jC. After 20 20 5 mm3 specimens were uniaxially pressed at 20 MPa, they were subjected to cold isostatic pressing at 200 MPa and sintered at 1200 jC for 2 h in air. The dielectric
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R. Li et al. / Solid State Ionics 172 (2004) 235–238
constants were measured using a pellet sample of 6 mm in diameter and 5 mm in thickness. The crystalline phase was determined by X-ray diffraction analysis using graphite monochromatized CuKa radiation (Shimadzu, XD-01). The fracture strength was measured by three-point bending at a crosshead speed of 0.5 mm min 1 and a span width of 10 mm (Shimadzu, Autograph AG-20kNG). The density of the sintered ceramic was measured using the Archimedes method. The dielectric constant and dielectric strength were measured by an impedance analyzer (Agilent Tech., 4299A) and a withstanding voltage tester (Kikusui, TOS5101), respectively. The planar dielectric barrier discharge-plasma reactor, whose shell was made of Teflon, was used for CO2 decomposition. The gas mixture (CO2/N2 = 10: 90) was fed into two parallel-plate electrodes (24 12 mm) made of stainless steel at a space velocity of 20,800 h 1, where the ground electrode was covered with a 1-mm-thick dielectric barrier (30 15 mm). The gap space between the dielectric barrier and the counter electrode was 1 mm and the CO2 decomposition was carried out under atmospheric pressure by using a conventional flow system. The concentration of CO2 dissociated by the DBD plasma was analyzed by a CO2 meter (Shimadzu URA107).
3. Results and discussion The characteristics of Ca0.7Sr0.3TiO3 sintered at 1200 jC for 2 h with and without Li2Si2O5 are listed in Table 1. The sintered bodies consisted of a single phase of orthorhombic Ca0.7Sr0.3TiO3 solid solution as reported in the previous papers according to the XRD analysis [7,8]. The relative density of the specimens dramatically increased by adding 0.5 wt.% Li2Si2O5 probably due to the liquid phase sintering, since the melting temperature of Li2Si2O5 is ca. 1030 jC. The three-point bending strength, Vickers hardness, dielectric strength and permittivity were also greatly increased by means of Li2Si2O5. The temperature dependencies of permittivities for Ca0.7Sr0.3TiO3 sintered at 1200 jC for 2 h with and without Li2Si2O5 are shown in Fig. 1 together with those of alumina and silica glass. Obviously, the permittivity of Ca0.7Sr0.3TiO3 with 0.5 wt.% Li2Si2O5 was much higher than those without an additive due to its higher density. The resulting rank order of permittivities was as follows: Ca0.7Sr0.3TiO3 with 0.5 wt.% Table 1 Properties of Ca0.7Sr0.3TiO3 sintered at 1200 jC for 2 h with and without Li2Si2O5 Li2Si2O5 content (wt.%)
Relative density (%)
Three-point bending strength (MPa)
KIC (MPam1/2)
Hv (GPa)
Dielectric strength (kVmm 1)
0.5 0
95.6 78.1
307 F 19 98 F 55
1.53 1.65
6.74 3.64
11.6 10.9
Fig. 1. Dielectric constants of Ca0.7Sr0.3TiO3 and commercial alumina and silica glass at 10 MHz. Ca0.7Sr0.3TiO3 with 0.5 wt.% Li2Si2O5; Ca0.7Sr0.3TiO3, without Li2Si2O5; Al2O3; SiO2.
Li2Si2O5HCa0.7Sr0.3TiO3 without an additiveHalumina (Al2O3)>silica glass (SiO2) at each temperature. Ca0.7Sr0.3TiO3 (0.5 wt.% additive), alumina and silica glass could successfully be used as the barrier materials to generate the DBD plasma reaction to decompose CO2; however, Ca0.7Sr0.3TiO3 without an additive was fractured before the initiation of the plasma. The input voltage was increased regularly with the time extending, until the plasma was generated and then kept it at the arcing voltage. The time dependencies of input voltage, power and conversion of CO2 are given in Fig. 2 for three kinds of dielectric barriers at the frequency of 10 kHz. The results using alumina and silica glass barriers were similar, i.e., the arcing voltage and CO2 conversion were ca. 3.5 kV and 3.8– 4.7%, respectively. On the other hand, in the case of the Ca0.7Sr0.3TiO3 barrier, the plasma generated at a much lower arcing voltage such as 2.1 kV, but the input power was much higher than those with alumina and silica glass barriers where CO2 conversion reached 15.6%. The effect of input frequency on the arcing voltage and CO2 conversion are shown in Fig. 3. In the case of this Ca0.7Sr0.3TiO3 barrier, the arcing voltage decreased and CO2 conversion increased with increasing input frequency. A similar trend was observed using alumina (Al2O3) and silica glass (SiO2) barriers, but the CO2 conversion was much lower. In addition, the plasma did not generate using an alumina and silica glass barriers at 12 kHz under the present reaction conditions. These results might be attributed to the much higher plasma power generated by using the Ca0.7Sr0.3TiO3 barrier than an alumina and silica glass barriers. Namely, the power of plasma seems to be the most important parameter in governing the CO2 decomposition because the plasma reaction is associated mainly with the energy provided [13].
R. Li et al. / Solid State Ionics 172 (2004) 235–238
Fig. 2. Time dependencies of input voltage, power and CO2 conversion using different dielectric barriers at 10 kHz. power; CO2 conversion.
The essential principle of the DBD plasma generation is shown as follows: C ¼ eS=d
ð1Þ
Q ¼ CV
ð2Þ
I ¼ Q=t
ð3Þ
P ¼ IV
ð4Þ
237
Input voltage;
input
average, have a kinetic energy which is higher than the energy corresponding to the random motion of the molecules, and this is just the inherent advantage of nonequilib-
where C = the electric capacity, e = permittivity, S = area of electrode, d = distance between parallel-plate electrodes, Q = electric charge, V = input voltage, I = electric current, t = time, and P = electric power. From Eqs. (1) – (4), Eq. (5) can be derived. P ¼ eSV 2 =td
ð5Þ
This is the reason that the reactivity of DBD plasma is improved by increasing the permittivity of the dielectric barrier based on the discharge physics. On the other hand, according to the mechanism of plasma chemistry, the important initiating reactions in the DBD plasma reaction are the collisions of ‘‘hot’’ electrons and the reactive constituents. These ‘‘hot’’ electrons, on the
Fig. 3. The relationships of input frequency with CO2 conversion and Ca0.7Sr0.3TiO3 with arcing voltage for different dielectric barriers. 0.5 wt.% Li2Si2O5; Al2O3; SiO2.
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R. Li et al. / Solid State Ionics 172 (2004) 235–238
rium DBD plasma [6]. Namely, all of the electrons are energetic enough and able to take part in the reaction in the DBD plasma. The ‘‘hot’’ electrons collide with CO2 molecules and excite them to higher energy levels to dissociate or initiate the reactions. The electron/molecular reaction can be described as [3– 5] CO2 þ e ! CO* 2 þ e ! CO þ 1=2O2 þ e
ð6Þ
where the asterisk * indicates the excited species. Based on Eq. (6), it could be found that the high electrons concentration corresponds to high rate of reaction and from Eqs. (1) and (2), Eq. (7) can be derived. Q ¼ eSV =d
ð7Þ
Eq. (7) suggested that the DBD plasma reaction (6) will be speeded up by using a higher permittivity barrier, i.e., more electrons.
4. Conclusions Using lower melting temperature additive of Li2Si2O5 could efficient improve the sinterability of Ca0.7Sr0.3TiO3 ceramic, and increase its relative density. The mechanical and dielectric properties were greatly enhanced by the liquid phase sintering. Different dielectric barrier materials resulted in different CO2 conversion, and the fraction depending on the dielectric constant of dielectric ceramics. Either according to the discharge physics and plasma chemistry or the results of experiments below conclusion could be obtained: the CO2 conversion was proportional to the permittivity of the dielectric barrier materials.
Acknowledgements This research was partially supported by the Ministry of Education, Culture, Sports, Science and Technology of Japan, a Grant-in-Aid for the COE project, Giant Molecules and Complex Systems, 2004, and by the Center for Interdisciplinary Research, Toholvu University. The authors are indebted to the management of Sakai Chemical Industry for supplying the starting powders used in the present study.
References [1] G. Zheng, J. Jiang, Y. Wu, R. Zhang, H. Hou, Plasma Chem. Plasma Process. 23 (2003) 59. [2] X. Xu, Thin Solid Films 390 (2001) 237. [3] H. Matsumoto, S. Tanabe, K. Okitsu, Y. Hayashi, S.L. Suib, Bull. Chem. Soc. Jpn. 72 (1999) 2567. [4] S.L. Brock, M. Marquez, S.L. Suib, Y. Hayashi, H. Matsumoto, J. Catal. 180 (1998) 225. [5] S.L. Suib, S.L. Brock, M. Marquez, J. Luo, H. Matsumoto, Y. Hayashi, J. Phys. Chem., B 102 (1998) 9661. [6] B. Eliasson, U. Kogelschatz, IEEE Trans. Plasma Sci. 19 (1991) 1063. [7] C.J. Ball, B.D. Begg, D.J. Cookson, G.J. Thorogood, E.R. Vance, J. Solid State Chem. 139 (1998) 238. [8] M. Ceh, D. Kolar, L. Golic, J. Solid State Chem. 68 (1987) 68. [9] S. Qin, A.I. Becerro, F. Seifert, J. Gottsmann, J. Jiang, J. Mater. Chem. 10 (2000) 1609. [10] C.J. Howard, R.L. Withers, B.J. Kennedy, J. Solid State Chem. 160 (2001) 8. [11] T. Yamanaka, N. Hirai, Y. Komatsu, Am. Mineral. 87 (2002) 1183. [12] B.S. Purwasasmita, E. Hoshi, T. Kimura, J. Ceram. Soc. Jpn. 109 (3) (2001) 191. [13] L. Hsieh, W. Lee, C. Li, C. Chen, Y. Wang, M. Chang, J. Chem. Technol. Biotechnol. 73 (1998) 432.
Influence of dielectric barrier materials to the behavior of dielectric barrier discharge plasma for CO2 decomposition Ruixing Li *, Yukishige Yamaguchi, Shu Yin, Qing Tang, Tsugio Sato Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan Received 9 November 2003; received in revised form 29 January 2004; accepted 26 February 2004
Abstract The aim of this study is to develop an application of dielectric ceramics in a dielectric barrier discharge (DBD) plasma reactor to dissociate CO2 to CO and O2. The fracture strength and dielectric strength of Ca0.7Sr0.3TiO3 were greatly improved by the liquid phase sintering using 0.5 wt.% Li2Si2O5 as a sintering additive. The sintered body was efficient when it was used as a dielectric barrier of a plasma reaction to generate a nonthermal plasma by the DBD. The ratio of CO2 decomposition by the DBD plasma using this Ca0.7Sr0.3TiO3 was much greater than with those using commercial alumina and silica glass barriers. This Ca0.7Sr0.3TiO3 ceramic was sintered using Li2Si2O5 as a sintering additive and used as a dielectric barrier of DBD for the first time. D 2004 Elsevier B.V. All rights reserved. PACS: 34.50.Gb; 34.50.Lf; 52.20.Hv; 52.75.Rx Keywords: Carbon dioxide; Decomposition; Plasma; Dielectric barrier discharge; SrTiO3; CaTiO3
1. Introduction Dielectric barrier discharge (DBD) plasmas are characterized by the presence of one or more insulating layers in the current path between the metal electrode in addition to the discharge gap(s), has been commercially used to produce ozone and has received attention for the application in pollution control, etc. [1– 5]. The dielectric barrier material is one of the key factors for the proper functioning of the DBD plasma [6]. The reactivity of DBD plasma is expected to be improved by increasing the permittivity of the dielectric barrier. However, the use of high dielectric constant ceramics is difficult, since these tend to be fractured when supplying high voltage because of their modest dielectric strength. Therefore, a dielectric barrier with a high dielectric constant and a high dielectric strength is highly desirable in order to generate a DBD plasma possessing high reactivity. It is known that SrTiO3 possesses a high permittivity and a modest dielectric strength. In contrast, CaTiO3 possesses a low dielectric constant and a high dielectric strength. According to the
* Corresponding author. Tel.: +81-22-2175598; fax: +81-22-2175597. E-mail address: [email protected] (R. Li). 0167-2738/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.ssi.2004.02.036
results of Ball [7] and Ceh et al. [8], CaTiO3 and SrTiO3 are completely miscible in forming the solid solution of Ca1 xSrxTiO3 (0 < x V 0.40). Therefore, Ca1 xSrxTiO3 is expected to possess high permittivity, high dielectric strength and to induce the reactive DBD plasma. Many works have been concerned with Ca1 xSrxTiO3 ceramic in the study of its phase transitions [7– 11], but the sintering behavior, dielectric properties and mechanical properties of Ca1 xSrxTiO3 have not been systematically investigated. Recently, it was reported that the sintering temperature of BaTiO3 could be greatly lowered without serious deterioration in the dielectric properties by using Li2Si2O5 [12]. In the present study, Ca0.7Sr0.3TiO3 was sintered using Li2Si2O5 as a sintering aid and used as a barrier material to generate the DBD plasma to decompose CO2 to CO.
2. Experimental procedures Appropriate quantities of CaTiO3, SrTiO3 and Li2Si2O5 were wet-mixed in a polyethylene bottle with ZrO2 balls and ethanol for 16 h and then dried at 85 jC. After 20 20 5 mm3 specimens were uniaxially pressed at 20 MPa, they were subjected to cold isostatic pressing at 200 MPa and sintered at 1200 jC for 2 h in air. The dielectric
236
R. Li et al. / Solid State Ionics 172 (2004) 235–238
constants were measured using a pellet sample of 6 mm in diameter and 5 mm in thickness. The crystalline phase was determined by X-ray diffraction analysis using graphite monochromatized CuKa radiation (Shimadzu, XD-01). The fracture strength was measured by three-point bending at a crosshead speed of 0.5 mm min 1 and a span width of 10 mm (Shimadzu, Autograph AG-20kNG). The density of the sintered ceramic was measured using the Archimedes method. The dielectric constant and dielectric strength were measured by an impedance analyzer (Agilent Tech., 4299A) and a withstanding voltage tester (Kikusui, TOS5101), respectively. The planar dielectric barrier discharge-plasma reactor, whose shell was made of Teflon, was used for CO2 decomposition. The gas mixture (CO2/N2 = 10: 90) was fed into two parallel-plate electrodes (24 12 mm) made of stainless steel at a space velocity of 20,800 h 1, where the ground electrode was covered with a 1-mm-thick dielectric barrier (30 15 mm). The gap space between the dielectric barrier and the counter electrode was 1 mm and the CO2 decomposition was carried out under atmospheric pressure by using a conventional flow system. The concentration of CO2 dissociated by the DBD plasma was analyzed by a CO2 meter (Shimadzu URA107).
3. Results and discussion The characteristics of Ca0.7Sr0.3TiO3 sintered at 1200 jC for 2 h with and without Li2Si2O5 are listed in Table 1. The sintered bodies consisted of a single phase of orthorhombic Ca0.7Sr0.3TiO3 solid solution as reported in the previous papers according to the XRD analysis [7,8]. The relative density of the specimens dramatically increased by adding 0.5 wt.% Li2Si2O5 probably due to the liquid phase sintering, since the melting temperature of Li2Si2O5 is ca. 1030 jC. The three-point bending strength, Vickers hardness, dielectric strength and permittivity were also greatly increased by means of Li2Si2O5. The temperature dependencies of permittivities for Ca0.7Sr0.3TiO3 sintered at 1200 jC for 2 h with and without Li2Si2O5 are shown in Fig. 1 together with those of alumina and silica glass. Obviously, the permittivity of Ca0.7Sr0.3TiO3 with 0.5 wt.% Li2Si2O5 was much higher than those without an additive due to its higher density. The resulting rank order of permittivities was as follows: Ca0.7Sr0.3TiO3 with 0.5 wt.% Table 1 Properties of Ca0.7Sr0.3TiO3 sintered at 1200 jC for 2 h with and without Li2Si2O5 Li2Si2O5 content (wt.%)
Relative density (%)
Three-point bending strength (MPa)
KIC (MPam1/2)
Hv (GPa)
Dielectric strength (kVmm 1)
0.5 0
95.6 78.1
307 F 19 98 F 55
1.53 1.65
6.74 3.64
11.6 10.9
Fig. 1. Dielectric constants of Ca0.7Sr0.3TiO3 and commercial alumina and silica glass at 10 MHz. Ca0.7Sr0.3TiO3 with 0.5 wt.% Li2Si2O5; Ca0.7Sr0.3TiO3, without Li2Si2O5; Al2O3; SiO2.
Li2Si2O5HCa0.7Sr0.3TiO3 without an additiveHalumina (Al2O3)>silica glass (SiO2) at each temperature. Ca0.7Sr0.3TiO3 (0.5 wt.% additive), alumina and silica glass could successfully be used as the barrier materials to generate the DBD plasma reaction to decompose CO2; however, Ca0.7Sr0.3TiO3 without an additive was fractured before the initiation of the plasma. The input voltage was increased regularly with the time extending, until the plasma was generated and then kept it at the arcing voltage. The time dependencies of input voltage, power and conversion of CO2 are given in Fig. 2 for three kinds of dielectric barriers at the frequency of 10 kHz. The results using alumina and silica glass barriers were similar, i.e., the arcing voltage and CO2 conversion were ca. 3.5 kV and 3.8– 4.7%, respectively. On the other hand, in the case of the Ca0.7Sr0.3TiO3 barrier, the plasma generated at a much lower arcing voltage such as 2.1 kV, but the input power was much higher than those with alumina and silica glass barriers where CO2 conversion reached 15.6%. The effect of input frequency on the arcing voltage and CO2 conversion are shown in Fig. 3. In the case of this Ca0.7Sr0.3TiO3 barrier, the arcing voltage decreased and CO2 conversion increased with increasing input frequency. A similar trend was observed using alumina (Al2O3) and silica glass (SiO2) barriers, but the CO2 conversion was much lower. In addition, the plasma did not generate using an alumina and silica glass barriers at 12 kHz under the present reaction conditions. These results might be attributed to the much higher plasma power generated by using the Ca0.7Sr0.3TiO3 barrier than an alumina and silica glass barriers. Namely, the power of plasma seems to be the most important parameter in governing the CO2 decomposition because the plasma reaction is associated mainly with the energy provided [13].
R. Li et al. / Solid State Ionics 172 (2004) 235–238
Fig. 2. Time dependencies of input voltage, power and CO2 conversion using different dielectric barriers at 10 kHz. power; CO2 conversion.
The essential principle of the DBD plasma generation is shown as follows: C ¼ eS=d
ð1Þ
Q ¼ CV
ð2Þ
I ¼ Q=t
ð3Þ
P ¼ IV
ð4Þ
237
Input voltage;
input
average, have a kinetic energy which is higher than the energy corresponding to the random motion of the molecules, and this is just the inherent advantage of nonequilib-
where C = the electric capacity, e = permittivity, S = area of electrode, d = distance between parallel-plate electrodes, Q = electric charge, V = input voltage, I = electric current, t = time, and P = electric power. From Eqs. (1) – (4), Eq. (5) can be derived. P ¼ eSV 2 =td
ð5Þ
This is the reason that the reactivity of DBD plasma is improved by increasing the permittivity of the dielectric barrier based on the discharge physics. On the other hand, according to the mechanism of plasma chemistry, the important initiating reactions in the DBD plasma reaction are the collisions of ‘‘hot’’ electrons and the reactive constituents. These ‘‘hot’’ electrons, on the
Fig. 3. The relationships of input frequency with CO2 conversion and Ca0.7Sr0.3TiO3 with arcing voltage for different dielectric barriers. 0.5 wt.% Li2Si2O5; Al2O3; SiO2.
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R. Li et al. / Solid State Ionics 172 (2004) 235–238
rium DBD plasma [6]. Namely, all of the electrons are energetic enough and able to take part in the reaction in the DBD plasma. The ‘‘hot’’ electrons collide with CO2 molecules and excite them to higher energy levels to dissociate or initiate the reactions. The electron/molecular reaction can be described as [3– 5] CO2 þ e ! CO* 2 þ e ! CO þ 1=2O2 þ e
ð6Þ
where the asterisk * indicates the excited species. Based on Eq. (6), it could be found that the high electrons concentration corresponds to high rate of reaction and from Eqs. (1) and (2), Eq. (7) can be derived. Q ¼ eSV =d
ð7Þ
Eq. (7) suggested that the DBD plasma reaction (6) will be speeded up by using a higher permittivity barrier, i.e., more electrons.
4. Conclusions Using lower melting temperature additive of Li2Si2O5 could efficient improve the sinterability of Ca0.7Sr0.3TiO3 ceramic, and increase its relative density. The mechanical and dielectric properties were greatly enhanced by the liquid phase sintering. Different dielectric barrier materials resulted in different CO2 conversion, and the fraction depending on the dielectric constant of dielectric ceramics. Either according to the discharge physics and plasma chemistry or the results of experiments below conclusion could be obtained: the CO2 conversion was proportional to the permittivity of the dielectric barrier materials.
Acknowledgements This research was partially supported by the Ministry of Education, Culture, Sports, Science and Technology of Japan, a Grant-in-Aid for the COE project, Giant Molecules and Complex Systems, 2004, and by the Center for Interdisciplinary Research, Toholvu University. The authors are indebted to the management of Sakai Chemical Industry for supplying the starting powders used in the present study.
References [1] G. Zheng, J. Jiang, Y. Wu, R. Zhang, H. Hou, Plasma Chem. Plasma Process. 23 (2003) 59. [2] X. Xu, Thin Solid Films 390 (2001) 237. [3] H. Matsumoto, S. Tanabe, K. Okitsu, Y. Hayashi, S.L. Suib, Bull. Chem. Soc. Jpn. 72 (1999) 2567. [4] S.L. Brock, M. Marquez, S.L. Suib, Y. Hayashi, H. Matsumoto, J. Catal. 180 (1998) 225. [5] S.L. Suib, S.L. Brock, M. Marquez, J. Luo, H. Matsumoto, Y. Hayashi, J. Phys. Chem., B 102 (1998) 9661. [6] B. Eliasson, U. Kogelschatz, IEEE Trans. Plasma Sci. 19 (1991) 1063. [7] C.J. Ball, B.D. Begg, D.J. Cookson, G.J. Thorogood, E.R. Vance, J. Solid State Chem. 139 (1998) 238. [8] M. Ceh, D. Kolar, L. Golic, J. Solid State Chem. 68 (1987) 68. [9] S. Qin, A.I. Becerro, F. Seifert, J. Gottsmann, J. Jiang, J. Mater. Chem. 10 (2000) 1609. [10] C.J. Howard, R.L. Withers, B.J. Kennedy, J. Solid State Chem. 160 (2001) 8. [11] T. Yamanaka, N. Hirai, Y. Komatsu, Am. Mineral. 87 (2002) 1183. [12] B.S. Purwasasmita, E. Hoshi, T. Kimura, J. Ceram. Soc. Jpn. 109 (3) (2001) 191. [13] L. Hsieh, W. Lee, C. Li, C. Chen, Y. Wang, M. Chang, J. Chem. Technol. Biotechnol. 73 (1998) 432.