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Preparation of Bi2O3–B2O3–ZnO–BaO–SiO2 glass powders with spherical shape by spray pyrolysis
Journal of Alloys and Compounds 437 (2007) 215–219
Preparation of Bi2O3–B2O3–ZnO–BaO–SiO2 glass powders with spherical shape by spray pyrolysis Seung Kwon Hong, Hye Young Koo, Dae Soo Jung, Il Soon Suh, Yun Chan Kang ∗ Department of Chemical Engineering, Konkuk University, 1 Hwayang-dong, Gwangjin-gu, Seoul 143-701, Republic of Korea Received 25 May 2006; received in revised form 15 July 2006; accepted 18 July 2006 Available online 30 August 2006
Abstract Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 glass powders were firstly prepared by spray pyrolysis. Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 glass powders prepared by spray pyrolysis had complete spherical shape and micron size at the optimum preparation temperatures. One micron-sized glass powder was formed from one droplet by drying, decomposition and melting processes. The dielectric layers formed from the glass powders prepared by spray pyrolysis had clean surface, dense inner structure, and high transparencies. The maximum transparency of the dielectric layer formed from the glass powders obtained by spray pyrolysis was 89% at the firing temperature of 580 ◦ C. The transparencies of the dielectric layers formed from the glass powders obtained by spray pyrolysis at preparation temperature of 1250 ◦ C decreased from 90 to 67% when the firing temperatures of the layers were changed from 580 to 520 ◦ C. © 2006 Elsevier B.V. All rights reserved. Keywords: Chemical synthesis; Gas–solid reaction; Amorphous materials
1. Introduction Glass powders are widely used as dielectric layers and fillers in various types of displays and ceramic capacitors [1–4]. Especially, plasma display panels (PDPs) use various types of glass powders for barrier ribs and dielectric layers of front and back panels. The dielectric layers of front panels used as protective layers for electrodes play key roles in PDPs. These layers should have a low dielectric constant, a high transparency, a high breakdown voltage, a low firing temperature, and a reasonable thermal expansion coefficient. The characteristics of transparent dielectric layers formed using the screen printing process are affected by the characteristics of the glass powder such as its composition, mean size, size distribution, and morphology. Pb-based glass powders are commercially used as transparent dielectric layers in PDPs. However, Pb component is deleterious to health of human and environment. Therefore, Pb-free glass powders are under developing in many research groups. Bi-based glass powders are widely studied as the raw materials
∗
Corresponding author. E-mail address: [email protected] (Y.C. Kang).
0925-8388/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2006.07.072
of transparent dielectric layers in PDPs because of their low firing temperature and high transparency [5]. Bi-based glass powders were generally formed from the melting process. The mixed powders of the reactants were ball-milled and melted in a platinum crucible at a high temperature [5]. Molten glasses were quenched to make glass flakes. The glass flakes were ground using various types of milling processes to obtain the glass powder. The ground glass powders were sieved to obtain the product with a narrow size distribution. The glass powder formed from the conventional melting process had an irregular morphology and a rough surface. Spray pyrolysis is one of the more promising processes for the preparation of improved ceramic and metal powders [6–12]. The powders synthesized by spray pyrolysis are relatively uniform in size and composition, spherical in shape, fine-sized, and have non-aggregation characteristics because of their microscale reaction within a droplet and the lack of a milling process. However, spray pyrolysis process did not well applied to the preparation of glass powders. In this study, Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 glass powders were directly prepared by high temperature spray pyrolysis. The characteristics of dielectric layers formed from the prepared Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 glass powders were investigated.
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2. Experimental Glass powders with a 42 wt% Bi2 O3 –23 wt% B2 O3 –19 wt% ZnO–13 wt% BaO–3 wt% SiO2 composition were directly prepared by high temperature spray pyrolysis. Small amount of alkaline earths materials were added as the additives. The spray pyrolysis equipment used consisted of six ultrasonic spray generators that operated at 1.7 MHz, a 1000-mm-long tubular alumina reactor of 50-mm
i.d., and a bag filter. The glass powders were prepared using spray pyrolysis at a temperature between 800 and 1350 ◦ C. The spray solutions were obtained by adding Bi2 O3 , H3 BO3 , BaCO3, ZnO, tetraethyl orthosilicate (TEOS) and nitric acid to distilled water. The overall solution concentration was 0.5 M. The spray solution was atomized with ultrasonic spray generators and introduced into a hot reaction column, where the droplets were dried, decomposed, and/or crystallized. The flow rate of air used as a carrier gas was 20 L/min.
Fig. 1. SEM photographs of glass powders prepared at different preparation temperatures. (a) 800 ◦ C; (b) 1000 ◦ C; (c) 1150 ◦ C; (d) 1200 ◦ C; (e) 1250 ◦ C; (f) 1300 ◦ C; (g) 1350 ◦ C.
S.K. Hong et al. / Journal of Alloys and Compounds 437 (2007) 215–219
217
Fig. 2. XRD spectra of glass powders prepared at different temperatures. Fig. 1. (Continued).
The glass transition temperature (Tg ) of the prepared glass powders was studied using differential thermal analysis (DTA). The crystal structures of the powders were studied using X-ray diffraction (XRD) with Cu K␣ radiation (λ = 1.5418). The morphologies of the powders were investigated using scanning electron microscopy (SEM).
3. Results and discussion The characteristics of the powders prepared by spray pyrolysis are affected by the preparation conditions such as preparation temperature and residence time of powders inside the hot wall reactor. Glass powders could be formed by melting and quenching process in the spray pyrolysis. Therefore, high preparation temperature and long residence time of powders inside the hot wall reactor are necessary to the preparation of glass powders in the spray pyrolysis. In this work, the optimum preparation temperature was investigated at the constant flow rate of carrier gas as 20 L/min. Fig. 1 shows the SEM photographs of the Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 powders prepared by spray pyrolysis at various preparation temperatures. The powders prepared at low temperatures below 1150 ◦ C had hollow structures and broad size distributions. The hollowness of the Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 powders increased with decreasing the preparation temperatures. The powders prepared at temperature of 800 ◦ C had thin wall structure. On the other hand, the powders prepared at high temperatures above 1200 ◦ C had complete spherical shape and dense structure. Melting of the Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 powders occurred at high preparation temperatures even at the short residence time of the powders inside the hot wall reactor. The sample prepared at high temperature of 1350 ◦ C had bimodal size distributions of nanosized and micron-sized powders. One micron-sized powder was formed from one droplet by drying, decomposition and melting processes. However, the nano-sized powders were formed by chemical vapor deposition process (CVD). Evaporation of the glass powders occurred at high preparation temperature. Nanosized powders were formed from the evaporated vapors by CVD process.
Fig. 2 shows the XRD spectra of the Bi2 O3 –B2 O3 –ZnO– BaO–SiO2 powders prepared by spray pyrolysis at various preparation temperatures. The Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 powders prepared at 800 ◦ C had crystalline structure, in which transition to the glass phase did not completely occurred. On the other hand, the Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 powders prepared by spray pyrolysis at temperatures above 1000 ◦ C had broad peaks at around 28◦ in the XRD spectra. The Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 glass powders were prepared by spray pyrolysis even within a short residence time of the powders inside the hot wall reactor. Fig. 3 shows the SEM photographs of the surfaces and the cross-sections of the dielectric layers formed from the Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 glass powders. The glass powders prepared by spray pyrolysis at preparation temperatures between 1150 and 1350 ◦ C were mixed with an organic vehicle that consisted of ethyl cellulose, ␣-terpineol, and butyl carbitol acetate (BCA). The glass transition temperature (Tg ) of the glass powders obtained by spray pyrolysis pyrolysis at preparation temperatures between 1150 and 1350 ◦ C was 407 ◦ C, regardless of the preparation temperatures. The glass paste was screenprinted onto the soda-lime glass substrate. The printed glass substrate was dried at 120 ◦ C for 30 min. The screen-printed glass substrate was fired by 2 steps, at first temperatures of 400 ◦ C for 10 min at a heating rate of 7 ◦ C and in the second temperatures of 580 ◦ C for 6 min at a heating rate of 7 ◦ C. The dielectric layers formed from the glass powders prepared by spray pyrolysis had clean surface and similar film thickness irrespective of the preparation temperatures. On the other hand, the inner structures of the dielectric layers were affected by the preparation temperatures of the Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 glass powders in the spray pyrolysis. The dielectric layer formed from the glass powders prepared by spray pyrolysis at preparation temperature of 1150 ◦ C had some voids inside the layer. The voids of the dielectric layers resulted from the hollow structure of the glass powders prepared by spray pyrolysis at preparation temperature of 1150 ◦ C. Melting of the hollow powders generates the void inside the dielectric layer. The number and mean size of the voids inside the dielectric layers decreased with increasing the preparation temperatures of the glass powders.
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Fig. 3. Cross-sections of dielectric layers formed from the glass powders prepared by spray pyrolysis. (a) 1150 ◦ C; (b) 1250 ◦ C; (c) 1300 ◦ C; (d) 1350 ◦ C.
The dielectric layers formed from the glass powders prepared by spray pyrolysis at preparation temperatures above 1300 ◦ C had clean surface and dense inner structure. Fig. 4 shows the transparencies of the dielectric layers formed from the Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 glass powders prepared by spray pyrolysis at different preparation temperatures. The transparency of the dielectric layer formed from the prepared glass powders was measured using a spectrophotometer in the visible light range. The screen-printed glass substrate was fired by 2 steps, at first temperatures of 400 ◦ C for 10 min at a heating rate of 7 ◦ C and in the second temperatures of 580 ◦ C for 6 min at a heating rate of 7 ◦ C. The thickness of the dielectric layers at firing temperature of 580 ◦ C was changed from 4.5 to 5 m when the preparation temperatures were varied from 1150 to 1350 ◦ C. Therefore, in this work, the transparencies of the dielectric layers were not affected by the thickness of the layers. The transparencies of the dielectric layers were affected by the characteristics of the Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 glass powders prepared by spray pyrolysis. The transparencies of the dielectric layers at firing temperature of 580 ◦ C decreased with increasing the preparation temperatures of the glass powders in the spray pyrolysis. The maximum transparency of the dielectric layer formed from the glass powders obtained by spray pyrolysis
at preparation temperature of 1150 ◦ C was 89%. On the other hand, the transparency of the dielectric layer formed from the glass powders obtained by spray pyrolysis at preparation temperature of 1350 ◦ C was 68% at firing temperature of 580 ◦ C. The
Fig. 4. Transparencies of dielectric layers formed from the glass powders prepared by spray pyrolysis.
S.K. Hong et al. / Journal of Alloys and Compounds 437 (2007) 215–219
219
powders obtained by spray pyrolysis at preparation temperature of 1250 ◦ C slightly decreased from 84 to 66% when the firing temperatures of the layers were changed from 580 to 520 ◦ C. At the same firing temperatures, the transparencies of the dielectric layers formed from the glass powders obtained by spray pyrolysis at preparation temperature of 1200 ◦ C were changed from 84 to 54%. Fig. 5 shows the relative transparencies of the dielectric layers formed from the Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 glass powders obtained by spray pyrolysis and the commercial PbO–B2 O3 –SiO2 glass powders. The commercial PbO–B2 O3 –SiO2 glass powders were prepared by conventional meting process. The dielectric layer formed from the Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 glass powders obtained by spray pyrolysis showed similar transparency with that of the dielectric layer formed from the commercial PbO–B2 O3 –SiO2 glass powders at firing temperature of 580 ◦ C. 4. Conclusions
Fig. 5. Transparencies of dielectric layers formed from the glass powders. (a) Spray pyrolysis (b) Commercial.
The possibility of the Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 glass powders prepared by spray pyrolysis as the law material of the transparent dielectric layer in the PDP was investigated. The preparation temperature in the spray pyrolysis was optimized to prepare the Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 glass powders with spherical shape and dense inner structure. Melting of the Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 powders occurred at high preparation temperatures even at the short residence time of the powders inside the hot wall reactor. The dielectric layers formed from the Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 glass powders obtained by spray pyrolysis had high transparencies even at low firing temperatures of the layers. Spray pyrolysis has also advantages in controlling the morphologies, mean sizes, and compositions of the glass powders. Therefore, Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 glass powders obtained by spray pyrolysis could be applied as the law material of the transparent dielectric layer in the PDP. References
change of compositions of the glass powders according to the preparation temperatures in the spray pyrolysis affected on the transparencies of the dielectric layers. The glass powders prepared by spray pyrolysis at high preparation temperatures had different compositions with those of the powders prepared at low preparation temperatures because of evaporation of the volatile components such as bismuth oxide and boron oxide. Therefore, the dielectric layer formed from the glass powders obtained by spray pyrolysis at preparation temperature of 1350 ◦ C had low transparency. The transparencies of the dielectric layers fired at different temperatures were also affected by the preparation temperatures of the glass powders. The transparencies of the dielectric layers formed from the glass powders obtained by spray pyrolysis at preparation temperature of 1150 ◦ C abruptly decreased from 89 to 43% when the firing temperatures of the layers were changed from 580 to 520 ◦ C. On the other hand, the transparencies of the dielectric layers formed from the glass
[1] P. Muralidharan, M. Venkateswarlu, N. Satyanarayana, J. Non-Cryst. Solids 351 (2005) 583. [2] D.N. Kim, J.Y. Lee, J.S. Huh, H.S. Kim, J. Non-Cryst. Solids 306 (2002) 70. [3] H.P. Jeon, S.K. Lee, S.W. Kim, D.K. Choi, Mater. Chem. Phys. 94 (2005) 185. [4] M.S. Chang, B.J. Pae, Y.K. Lee, B.G. Ryu, M.H. Park, J. Inform. Display 2 (2001) 39. [5] J.Y. Song, S.Y Choi, Displays, in press. [6] T.C. Pluym, T.T. Kodas, J. Mater. Res. 10 (1995) 1661. [7] Y.C. Kang, I.W. Lenggoro, K. Okuyama, S.B. Park, J. Electrochem. Soc. 146 (3) (1997) 1227. [8] Y.C. Kang, H.S. Roh, S.B. Park, Adv. Mater. 12 (2000) 451. [9] G.L. Messing, S.C. Zhang, G.V. Jayanthi, J. Am. Ceram. Soc. 76 (1993) 2707. [10] A. Gurav, T. Kodas, T. Pluym, Y. Xiong, Aerosol Sci. Technol. 19 (1993) 411. [11] K.H. Leong, J. Aerosol Sci. 18 (1987) 511. [12] C.S. Zhang, G.L. Messing, W. Huebner, J. Aerosol Sci. 22 (1991) 585.
Preparation of Bi2O3–B2O3–ZnO–BaO–SiO2 glass powders with spherical shape by spray pyrolysis Seung Kwon Hong, Hye Young Koo, Dae Soo Jung, Il Soon Suh, Yun Chan Kang ∗ Department of Chemical Engineering, Konkuk University, 1 Hwayang-dong, Gwangjin-gu, Seoul 143-701, Republic of Korea Received 25 May 2006; received in revised form 15 July 2006; accepted 18 July 2006 Available online 30 August 2006
Abstract Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 glass powders were firstly prepared by spray pyrolysis. Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 glass powders prepared by spray pyrolysis had complete spherical shape and micron size at the optimum preparation temperatures. One micron-sized glass powder was formed from one droplet by drying, decomposition and melting processes. The dielectric layers formed from the glass powders prepared by spray pyrolysis had clean surface, dense inner structure, and high transparencies. The maximum transparency of the dielectric layer formed from the glass powders obtained by spray pyrolysis was 89% at the firing temperature of 580 ◦ C. The transparencies of the dielectric layers formed from the glass powders obtained by spray pyrolysis at preparation temperature of 1250 ◦ C decreased from 90 to 67% when the firing temperatures of the layers were changed from 580 to 520 ◦ C. © 2006 Elsevier B.V. All rights reserved. Keywords: Chemical synthesis; Gas–solid reaction; Amorphous materials
1. Introduction Glass powders are widely used as dielectric layers and fillers in various types of displays and ceramic capacitors [1–4]. Especially, plasma display panels (PDPs) use various types of glass powders for barrier ribs and dielectric layers of front and back panels. The dielectric layers of front panels used as protective layers for electrodes play key roles in PDPs. These layers should have a low dielectric constant, a high transparency, a high breakdown voltage, a low firing temperature, and a reasonable thermal expansion coefficient. The characteristics of transparent dielectric layers formed using the screen printing process are affected by the characteristics of the glass powder such as its composition, mean size, size distribution, and morphology. Pb-based glass powders are commercially used as transparent dielectric layers in PDPs. However, Pb component is deleterious to health of human and environment. Therefore, Pb-free glass powders are under developing in many research groups. Bi-based glass powders are widely studied as the raw materials
∗
Corresponding author. E-mail address: [email protected] (Y.C. Kang).
0925-8388/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2006.07.072
of transparent dielectric layers in PDPs because of their low firing temperature and high transparency [5]. Bi-based glass powders were generally formed from the melting process. The mixed powders of the reactants were ball-milled and melted in a platinum crucible at a high temperature [5]. Molten glasses were quenched to make glass flakes. The glass flakes were ground using various types of milling processes to obtain the glass powder. The ground glass powders were sieved to obtain the product with a narrow size distribution. The glass powder formed from the conventional melting process had an irregular morphology and a rough surface. Spray pyrolysis is one of the more promising processes for the preparation of improved ceramic and metal powders [6–12]. The powders synthesized by spray pyrolysis are relatively uniform in size and composition, spherical in shape, fine-sized, and have non-aggregation characteristics because of their microscale reaction within a droplet and the lack of a milling process. However, spray pyrolysis process did not well applied to the preparation of glass powders. In this study, Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 glass powders were directly prepared by high temperature spray pyrolysis. The characteristics of dielectric layers formed from the prepared Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 glass powders were investigated.
216
S.K. Hong et al. / Journal of Alloys and Compounds 437 (2007) 215–219
2. Experimental Glass powders with a 42 wt% Bi2 O3 –23 wt% B2 O3 –19 wt% ZnO–13 wt% BaO–3 wt% SiO2 composition were directly prepared by high temperature spray pyrolysis. Small amount of alkaline earths materials were added as the additives. The spray pyrolysis equipment used consisted of six ultrasonic spray generators that operated at 1.7 MHz, a 1000-mm-long tubular alumina reactor of 50-mm
i.d., and a bag filter. The glass powders were prepared using spray pyrolysis at a temperature between 800 and 1350 ◦ C. The spray solutions were obtained by adding Bi2 O3 , H3 BO3 , BaCO3, ZnO, tetraethyl orthosilicate (TEOS) and nitric acid to distilled water. The overall solution concentration was 0.5 M. The spray solution was atomized with ultrasonic spray generators and introduced into a hot reaction column, where the droplets were dried, decomposed, and/or crystallized. The flow rate of air used as a carrier gas was 20 L/min.
Fig. 1. SEM photographs of glass powders prepared at different preparation temperatures. (a) 800 ◦ C; (b) 1000 ◦ C; (c) 1150 ◦ C; (d) 1200 ◦ C; (e) 1250 ◦ C; (f) 1300 ◦ C; (g) 1350 ◦ C.
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217
Fig. 2. XRD spectra of glass powders prepared at different temperatures. Fig. 1. (Continued).
The glass transition temperature (Tg ) of the prepared glass powders was studied using differential thermal analysis (DTA). The crystal structures of the powders were studied using X-ray diffraction (XRD) with Cu K␣ radiation (λ = 1.5418). The morphologies of the powders were investigated using scanning electron microscopy (SEM).
3. Results and discussion The characteristics of the powders prepared by spray pyrolysis are affected by the preparation conditions such as preparation temperature and residence time of powders inside the hot wall reactor. Glass powders could be formed by melting and quenching process in the spray pyrolysis. Therefore, high preparation temperature and long residence time of powders inside the hot wall reactor are necessary to the preparation of glass powders in the spray pyrolysis. In this work, the optimum preparation temperature was investigated at the constant flow rate of carrier gas as 20 L/min. Fig. 1 shows the SEM photographs of the Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 powders prepared by spray pyrolysis at various preparation temperatures. The powders prepared at low temperatures below 1150 ◦ C had hollow structures and broad size distributions. The hollowness of the Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 powders increased with decreasing the preparation temperatures. The powders prepared at temperature of 800 ◦ C had thin wall structure. On the other hand, the powders prepared at high temperatures above 1200 ◦ C had complete spherical shape and dense structure. Melting of the Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 powders occurred at high preparation temperatures even at the short residence time of the powders inside the hot wall reactor. The sample prepared at high temperature of 1350 ◦ C had bimodal size distributions of nanosized and micron-sized powders. One micron-sized powder was formed from one droplet by drying, decomposition and melting processes. However, the nano-sized powders were formed by chemical vapor deposition process (CVD). Evaporation of the glass powders occurred at high preparation temperature. Nanosized powders were formed from the evaporated vapors by CVD process.
Fig. 2 shows the XRD spectra of the Bi2 O3 –B2 O3 –ZnO– BaO–SiO2 powders prepared by spray pyrolysis at various preparation temperatures. The Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 powders prepared at 800 ◦ C had crystalline structure, in which transition to the glass phase did not completely occurred. On the other hand, the Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 powders prepared by spray pyrolysis at temperatures above 1000 ◦ C had broad peaks at around 28◦ in the XRD spectra. The Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 glass powders were prepared by spray pyrolysis even within a short residence time of the powders inside the hot wall reactor. Fig. 3 shows the SEM photographs of the surfaces and the cross-sections of the dielectric layers formed from the Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 glass powders. The glass powders prepared by spray pyrolysis at preparation temperatures between 1150 and 1350 ◦ C were mixed with an organic vehicle that consisted of ethyl cellulose, ␣-terpineol, and butyl carbitol acetate (BCA). The glass transition temperature (Tg ) of the glass powders obtained by spray pyrolysis pyrolysis at preparation temperatures between 1150 and 1350 ◦ C was 407 ◦ C, regardless of the preparation temperatures. The glass paste was screenprinted onto the soda-lime glass substrate. The printed glass substrate was dried at 120 ◦ C for 30 min. The screen-printed glass substrate was fired by 2 steps, at first temperatures of 400 ◦ C for 10 min at a heating rate of 7 ◦ C and in the second temperatures of 580 ◦ C for 6 min at a heating rate of 7 ◦ C. The dielectric layers formed from the glass powders prepared by spray pyrolysis had clean surface and similar film thickness irrespective of the preparation temperatures. On the other hand, the inner structures of the dielectric layers were affected by the preparation temperatures of the Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 glass powders in the spray pyrolysis. The dielectric layer formed from the glass powders prepared by spray pyrolysis at preparation temperature of 1150 ◦ C had some voids inside the layer. The voids of the dielectric layers resulted from the hollow structure of the glass powders prepared by spray pyrolysis at preparation temperature of 1150 ◦ C. Melting of the hollow powders generates the void inside the dielectric layer. The number and mean size of the voids inside the dielectric layers decreased with increasing the preparation temperatures of the glass powders.
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Fig. 3. Cross-sections of dielectric layers formed from the glass powders prepared by spray pyrolysis. (a) 1150 ◦ C; (b) 1250 ◦ C; (c) 1300 ◦ C; (d) 1350 ◦ C.
The dielectric layers formed from the glass powders prepared by spray pyrolysis at preparation temperatures above 1300 ◦ C had clean surface and dense inner structure. Fig. 4 shows the transparencies of the dielectric layers formed from the Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 glass powders prepared by spray pyrolysis at different preparation temperatures. The transparency of the dielectric layer formed from the prepared glass powders was measured using a spectrophotometer in the visible light range. The screen-printed glass substrate was fired by 2 steps, at first temperatures of 400 ◦ C for 10 min at a heating rate of 7 ◦ C and in the second temperatures of 580 ◦ C for 6 min at a heating rate of 7 ◦ C. The thickness of the dielectric layers at firing temperature of 580 ◦ C was changed from 4.5 to 5 m when the preparation temperatures were varied from 1150 to 1350 ◦ C. Therefore, in this work, the transparencies of the dielectric layers were not affected by the thickness of the layers. The transparencies of the dielectric layers were affected by the characteristics of the Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 glass powders prepared by spray pyrolysis. The transparencies of the dielectric layers at firing temperature of 580 ◦ C decreased with increasing the preparation temperatures of the glass powders in the spray pyrolysis. The maximum transparency of the dielectric layer formed from the glass powders obtained by spray pyrolysis
at preparation temperature of 1150 ◦ C was 89%. On the other hand, the transparency of the dielectric layer formed from the glass powders obtained by spray pyrolysis at preparation temperature of 1350 ◦ C was 68% at firing temperature of 580 ◦ C. The
Fig. 4. Transparencies of dielectric layers formed from the glass powders prepared by spray pyrolysis.
S.K. Hong et al. / Journal of Alloys and Compounds 437 (2007) 215–219
219
powders obtained by spray pyrolysis at preparation temperature of 1250 ◦ C slightly decreased from 84 to 66% when the firing temperatures of the layers were changed from 580 to 520 ◦ C. At the same firing temperatures, the transparencies of the dielectric layers formed from the glass powders obtained by spray pyrolysis at preparation temperature of 1200 ◦ C were changed from 84 to 54%. Fig. 5 shows the relative transparencies of the dielectric layers formed from the Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 glass powders obtained by spray pyrolysis and the commercial PbO–B2 O3 –SiO2 glass powders. The commercial PbO–B2 O3 –SiO2 glass powders were prepared by conventional meting process. The dielectric layer formed from the Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 glass powders obtained by spray pyrolysis showed similar transparency with that of the dielectric layer formed from the commercial PbO–B2 O3 –SiO2 glass powders at firing temperature of 580 ◦ C. 4. Conclusions
Fig. 5. Transparencies of dielectric layers formed from the glass powders. (a) Spray pyrolysis (b) Commercial.
The possibility of the Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 glass powders prepared by spray pyrolysis as the law material of the transparent dielectric layer in the PDP was investigated. The preparation temperature in the spray pyrolysis was optimized to prepare the Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 glass powders with spherical shape and dense inner structure. Melting of the Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 powders occurred at high preparation temperatures even at the short residence time of the powders inside the hot wall reactor. The dielectric layers formed from the Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 glass powders obtained by spray pyrolysis had high transparencies even at low firing temperatures of the layers. Spray pyrolysis has also advantages in controlling the morphologies, mean sizes, and compositions of the glass powders. Therefore, Bi2 O3 –B2 O3 –ZnO–BaO–SiO2 glass powders obtained by spray pyrolysis could be applied as the law material of the transparent dielectric layer in the PDP. References
change of compositions of the glass powders according to the preparation temperatures in the spray pyrolysis affected on the transparencies of the dielectric layers. The glass powders prepared by spray pyrolysis at high preparation temperatures had different compositions with those of the powders prepared at low preparation temperatures because of evaporation of the volatile components such as bismuth oxide and boron oxide. Therefore, the dielectric layer formed from the glass powders obtained by spray pyrolysis at preparation temperature of 1350 ◦ C had low transparency. The transparencies of the dielectric layers fired at different temperatures were also affected by the preparation temperatures of the glass powders. The transparencies of the dielectric layers formed from the glass powders obtained by spray pyrolysis at preparation temperature of 1150 ◦ C abruptly decreased from 89 to 43% when the firing temperatures of the layers were changed from 580 to 520 ◦ C. On the other hand, the transparencies of the dielectric layers formed from the glass
[1] P. Muralidharan, M. Venkateswarlu, N. Satyanarayana, J. Non-Cryst. Solids 351 (2005) 583. [2] D.N. Kim, J.Y. Lee, J.S. Huh, H.S. Kim, J. Non-Cryst. Solids 306 (2002) 70. [3] H.P. Jeon, S.K. Lee, S.W. Kim, D.K. Choi, Mater. Chem. Phys. 94 (2005) 185. [4] M.S. Chang, B.J. Pae, Y.K. Lee, B.G. Ryu, M.H. Park, J. Inform. Display 2 (2001) 39. [5] J.Y. Song, S.Y Choi, Displays, in press. [6] T.C. Pluym, T.T. Kodas, J. Mater. Res. 10 (1995) 1661. [7] Y.C. Kang, I.W. Lenggoro, K. Okuyama, S.B. Park, J. Electrochem. Soc. 146 (3) (1997) 1227. [8] Y.C. Kang, H.S. Roh, S.B. Park, Adv. Mater. 12 (2000) 451. [9] G.L. Messing, S.C. Zhang, G.V. Jayanthi, J. Am. Ceram. Soc. 76 (1993) 2707. [10] A. Gurav, T. Kodas, T. Pluym, Y. Xiong, Aerosol Sci. Technol. 19 (1993) 411. [11] K.H. Leong, J. Aerosol Sci. 18 (1987) 511. [12] C.S. Zhang, G.L. Messing, W. Huebner, J. Aerosol Sci. 22 (1991) 585.