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Li2TiO3 powder synthesis by solid-state reaction and pebble fabrication for tritium breeding material
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ARTICLE IN PRESS
FUSION-9499; No. of Pages 5
Fusion Engineering and Design xxx (2017) xxx–xxx
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Li2 TiO3 powder synthesis by solid-state reaction and pebble fabrication for tritium breeding material Yi-Hyun Park ∗ , Kyung-Mi Min, Seungyon Cho, Mu-Young Ahn, Young-Min Lee National Fusion Research Institute (NFRI), Daejeon, Republic of Korea
h i g h l i g h t s • • • •
The Li2 TiO3 nano-powders were successfully synthesized by solid-state reaction process. The average particle size of synthesized Li2 TiO3 nano-powder was approximately 150 nm. The optimization of synthesis conditions for high crystalline structure and fine particle was conducted. The Li2 TiO3 pebbles with diameter of 1 mm and high uniformity were successfully fabricated by using the synthesized nano-powder.
a r t i c l e
i n f o
Article history: Received 3 October 2016 Received in revised form 27 April 2017 Accepted 4 May 2017 Available online xxx Keywords: Lithium metatitanate (Li2 TiO3 ) Nano-powder Tritium breeder Pebble Solid-state reaction
a b s t r a c t The tritium breeding materials require small particle size to reduce the diffusion distance of generated tritium in the intercrystalline. In addition, the essential resource, especially enriched Li-6, has to be recovered from the used tritium breeding material. For the hands-on operation during the recovery process, the activation level of the used breeder is strictly limited in order to reduce the impurities of long-lived radioactive nuclides in the tritium breeding material. In this study, lithium oxide (Li2 O) and titanium dioxide (TiO2 ) were used as starting materials in the synthesis of Li2 TiO3 powder. The starting materials were mixed by wet ball-milling process. The mixed powders were synthesized by heat treatment. The average particle size of synthesized Li2 TiO3 powder was approximately 150 nm. And, the long-lived radioactive nuclides, such as aluminum (Al) and cobalt (Co), were not accumulated in the synthesized Li2 TiO3 powder during the synthesis process. The Li2 TiO3 pebbles were fabricated by slurry droplet wetting method using the synthesized Li2 TiO3 nano-powder. The particle size, crush load, and porosity of fabricated Li2 TiO3 pebbles using the synthesized nano-powder were investigated. © 2017 Elsevier B.V. All rights reserved.
1. Introduction Lithium-containing ceramics compounds, such as lithium metatitanate (Li2 TiO3 ) and lithium orthosilicate (Li4 SiO4 ), are used as solid-type of tritium breeder materials for fusion breeding blankets. The tritium breeder materials require small particle size to reduce the bulk diffusion of bred tritium in the intercrystalline of breeder materials [1]. In addition, the essential resource, especially enriched Li-6, has to be recovered from the used tritium breeder materials. For the hands-on operation during the recovery process, the contents of long-lived radioactive nuclides, especially aluminum (Al) and cobalt (Co) in the tritium breeder materials are strictly limited in order to reduce the activation level of used breeder materials [2].
∗ Corresponding author. E-mail address: [email protected] (Y.-H. Park).
This study aims at the fabrication of Li2 TiO3 pebbles, which have a small particle size and low levels of the long-lived radioactive nuclides, by using solid-state reaction process [3,4]. The pebble fabrication method has been developed for application to mass-production of tritium breeder pebbles [5,6]. This method is slurry-based process and adopting to use Li2 TiO3 powder for the preparation of slurry. Therefore, the Li2 TiO3 nano-powder with high purity was synthesized by solid-state reaction process. Lithium oxide (Li2 O) and titanium dioxide (TiO2 ) were used as starting materials for the synthesis of Li2 TiO3 nano-powder. The starting materials were directly reacted at high temperature. The synthesized Li2 TiO3 nano-powder was used for the fabrication of pebbles. The effects of heat treatment temperature, heat treatment time, and molar ratio of starting materials on the synthesized Li2 TiO3 powder were investigated. In addition, the characterization of the fabricated Li2 TiO3 pebbles using synthesized nano-powder, such as diameter, grain size, porosity and crush load, were performed in this work.
http://dx.doi.org/10.1016/j.fusengdes.2017.05.015 0920-3796/© 2017 Elsevier B.V. All rights reserved.
Please cite this article in press as: Y.-H. Park, et al., Li2 TiO3 powder synthesis by solid-state reaction and pebble fabrication for tritium breeding material, Fusion Eng. Des. (2017), http://dx.doi.org/10.1016/j.fusengdes.2017.05.015
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Fig. 1. XRD patterns of synthesized Li2 TiO3 powders at different heat treatment temperatures.
2. Experiments
Microstructure of pebble surface and fractured surface after crush test was observed by SEM.
2.1. Powder synthesis 3. Results and discussion Lithium oxide (Li2 O) and titanium dioxide (TiO2 ) were used as starting materials for the synthesis of high purity Li2 TiO3 nanopowder. Two kinds of TiO2 forms, anatase and rutile, were used for the investigation of the effects on crystalline structure of synthesized Li2 TiO3 powder. The purities of Li2 O, rutile-TiO2 , and anatase-TiO2 were 99%, 99.99%, and 99.9%, respectively. The starting materials were mixed by wet ball-mill process using isopropyl alcohol as solvent during 3 h. The molar ratio of Li2 O versus TiO2 was 1.000 versus 0.890–1.000. The mixed powders were dried at 60 ◦ C in vacuum oven more than 6 h. The dried powders were heat treated in air atmosphere at 500–800 ◦ C for 2–24 h. The morphology of synthesized powder was observed by scanning electron microscope (SEM). The particle size was measured by image analysis technique through the SEM image. The crystalline structure and phase analysis were carried out by X-ray diffraction (XRD) patterns. The impurities, especially Al and Co, of starting powders and synthesized powders were determined by inductively coupled plasma optical emission spectrometry (ICP-OES).
2.2. Pebble fabrication The Li2 TiO3 pebbles were fabricated by slurry droplet wetting method, which had been developed for the fabrication of tritium breeder pebbles with highly uniformed sizes considering mass-production. The detailed procedure of pebble fabrication was presented in previous works [3,4]. The Li2 TiO3 pebbles were sintered at 1000 ◦ C for 3 h in air atmosphere. The diameters of sintered pebbles were measured by image analysis technique through the optical microscope images. The open and closed porosity of sintered pebbles were measured by Archimedes method and helium pycnometer. The crush loads of sintered pebbles were measured by screw-driven universal material testing machine, Instron 5969, at room temperature. The cross-head speed and capacity of load cell was 0.1 mm/min and 100 N, respectively. A total of 55 pebbles were tested and analyzed.
3.1. Effect of heat treatment temperature The effects of heat treatment temperature on the synthesis of Li2 TiO3 was investigated. The XRD patterns of synthesized Li2 TiO3 powders at different temperatures are shown in Fig. 1. Fig. 1(a) and (b) represents the XRD patterns of synthesized powder using rutile-TiO2 and anatase-TiO2 as starting material, respectively. In the case of using rutile-TiO2 , as shown in Fig. 1(a), the residual TiO2 was detected in the synthesized powder even though they reacted at 700 ◦ C. The amount of residual TiO2 was decreased as heat treatment temperature increases. However, the synthesized powder at 800 ◦ C included the secondary phase which was identified as Li4 Ti5 O12 . Whereas, in the case of using anatase-TiO2 , the residual TiO2 was not detected in the synthesized powder as shown in Fig. 1(b). However, unknown peaks in the synthesized powder at 650 ◦ C and 660 ◦ C were detected at 2 between 30◦ and 32◦ . The unknown phases could be avoided by increasing heat treatment temperature. When the heat treatment temperature was above 670 ◦ C, the unknown peaks in the synthesized powder disappeared. Namely, the heat treated Li2 TiO3 powder using anatase-TiO2 above 670 ◦ C was able to be synthesized with high crystalline structure. 3.2. Effect of heat treatment time The effects of heat treatment time on the crystalline structure of synthesized Li2 TiO3 powder were investigated. Fig. 2 shows the XRD patterns of synthesized powder at 700 ◦ C for different heat treatment time. Fig. 2(a) and (b) represents the XRD patterns of synthesized powders using rutile-TiO2 and anatase-TiO2 as starting material, respectively. The crystalline structure was identified from the reference pattern of monoclinic Li2 TiO3 (JCPDS No. 77–8280). According to the reference pattern, the first and second peaks of the monoclinic Li2 TiO3 are located at 2 = 18.44◦ and 2 = 43.68◦ , respectively. In other words, the peak intensity of 18.44◦ is higher than that of 43.68◦ . However, in the case of using rutile-TiO2 , the
Please cite this article in press as: Y.-H. Park, et al., Li2 TiO3 powder synthesis by solid-state reaction and pebble fabrication for tritium breeding material, Fusion Eng. Des. (2017), http://dx.doi.org/10.1016/j.fusengdes.2017.05.015
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Fig. 2. XRD patterns of synthesized Li2 TiO3 powders at different heat treatment time.
first peak intensity of a whole synthesized powder was lower than second peak intensity as shown in Fig. 2(a). It means that the heat treatment time greater than 24 h is needed for the high crystalline structure of synthesized Li2 TiO3 powder using rutile-TiO2 . On the other hand, as shown in Fig. 2(b), the first peak intensities of a whole synthesized powder using anatase-TiO2 were the same or higher than the second peak intensities. However, the unknown peaks in the heat treated powder below 6 h were also detected at 2 between 30◦ and 32◦ . The unknown phases disappeared when the heat treatment time was greater than 12 h. Therefore, the appropriate heat treatment time for high crystalline structure of synthesized Li2 TiO3 powder was 12 h.
3.3. Effect of molar ratio The effects of molar ratio of starting materials on the crystalline structure of synthesized Li2 TiO3 powder were investigated. The XRD patterns of synthesized powder using several molar ratios of Li2 O and TiO2 were represented in Fig. 3. The TiO2 was remaining in the synthesized powders using high rutile-TiO2 ratio as shown in Fig. 3(a). The residual TiO2 was able to be removed by reducing the TiO2 ratio to below 0.942. However, the intensity of first peaks was lower than that of second peaks. Whereas a whole synthesized powder using anatase-TiO2 had a high crystalline structure. In other words, the Li2 TiO3 powder with high crystalline structure was able to be synthesized at wide range of molar ratio between Li2 O and anatase-TiO2 , as shown in Fig. 3(b).
Fig. 3. XRD patterns of synthesized Li2 TiO3 powders by different molar ratio of starting materials.
Please cite this article in press as: Y.-H. Park, et al., Li2 TiO3 powder synthesis by solid-state reaction and pebble fabrication for tritium breeding material, Fusion Eng. Des. (2017), http://dx.doi.org/10.1016/j.fusengdes.2017.05.015
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Fig. 5. Optical microscope image of sintered Li2 TiO3 pebbles.
Fig. 4. Morphology of synthesized Li2 TiO3 nano-powder.
3.4. Characteristics of synthesized powder The SEM images of synthesized Li2 TiO3 powders at 700 ◦ C for 12 h with molar ratio of 0.942 are shown in Fig. 4(a) and (b). The average particle sizes of the synthesized powder using rutile-TiO2 and anatase-TiO2 were 500 nm and 150 nm, respectively. The shape of synthesized Li2 TiO3 nano-powder was spherical type. As a result of elemental analysis, Co impurity was not included in the synthesized Li2 TiO3 nano-powders using rutile-TiO2 and anatase-TiO2 as starting material. Al contents in the synthesized powder using rutile-TiO2 and anatase-TiO2 were about 30.89 ppm and 33.18 ppm, respectively. It was estimated that the Al impurity came from starting materials. The Al contents of Li2 O and rutile-TiO2 were 49.49 ppm and 13.8 ppm, respectively. However, the level of Al contents in the synthesized Li2 TiO3 nano-powder is allowable for the hands-on operation during the recovery process of essential resource, especially enriched Li-6, from used breeder materials [2]. 3.5. Properties of sintered pebbles The morphology of fabricated Li2 TiO3 pebbles using nanopowder, which is synthesized using anatase-TiO2 (Fig. 4(b)), are shown in Fig. 5. The average diameter of sintered pebbles was 1.00 mm. And they had a high uniformity and good sphericity, as shown in Fig. 5. The microstructures of surface of sintered pebble and fractured surface after crush load are shown in Fig. 6(a) and (b), respectively. The grain size of sintered pebbles was from 5 m to 40 m in spite of using synthesized Li2 TiO3 nano-powder which had an average particle size of 150 nm. Namely, the excessive and abnormal grain growth was occurred during sintering process. The main type of pores was a closed pore, which was primarily
Fig. 6. SEM images of sintered Li2 TiO3 pebbles.
formed at a triple point of grains, as shown in Fig. 6(b). The open and closed porosity of sintered pebbles were measured as 0.2% and 6.5%, respectively. The measured density of sintered pebbles was about 3.17 g/cm3 . The average crush load of sintered Li2 TiO3 pebbles was approximately 7.5 N (Fig. 7). It was relatively low because they had a lot of defects by excessive sintering, such as bumps, cracks on the surface, and so on. When the Li2 TiO3 pebbles were
Please cite this article in press as: Y.-H. Park, et al., Li2 TiO3 powder synthesis by solid-state reaction and pebble fabrication for tritium breeding material, Fusion Eng. Des. (2017), http://dx.doi.org/10.1016/j.fusengdes.2017.05.015
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150 nm. The long-lived radioactive nuclides were not detected in the synthesized Li2 TiO3 nano-powder during this synthesis process. The Li2 TiO3 pebbles with diameter of 1 mm and high uniformity were successfully fabricated using the synthesized nano-powder. However, the optimization of sintering conditions for the use of the Li2 TiO3 nano-powder will be necessary in order to improve the Li2 TiO3 pebble properties. Acknowledgments
Fig. 7. Diameter and crush load of sintered Li2 TiO3 pebbles.
sintered at 1000 ◦ C for 3 h. The sintering conditions has been optimized for using commercial Li2 TiO3 powder with particle size of 12 m. Therefore, according to the results of characteristics of sintered pebbles, the optimization of sintering conditions for using Li2 TiO3 nano-powder is strongly needed in order to improve the pebble characteristics. 4. Conclusions The effects of TiO2 forms as starting material, rutile and anatase, on the characteristics of synthesized Li2 TiO3 nano-powder were investigated. It was found that the anatase-TiO2 was suitable for synthesis of Li2 TiO3 nano-powder with high crystalline structure and fine particle. The average particle size was approximately
This work was supported by the R&D Program through the National Fusion Research Institute (NFRI) funded by the Ministry of Science, ICT and Future Planning of the Republic of Korea (NFRIIN1603). References [1] C.E. Johnson, et al., Ceramic breeder materials: status and needs, J. Nucl. Mater. 258–263 (1998) 140–148. [2] U. Fischer, H. Tsige-Tamirat, Activation characteristics of a solid breeder blanket for a fusion power demonstration reactor, J. Nucl. Mater. 307–311 (2002) 798–802. [3] Jean-Daniel Lulewicz, Nicole Roux, First results of the investigation of Li2 ZrO3 and Li2 TiO3 pebbles, Fusion Eng. Des. 39–40 (1998) 745–750. [4] Seiya Ogawa, et al., Li vaporization property of two-phase material of Li2 TiO3 and Li2 SiO3 for tritium breeder, Fusion Eng. Des. 98–99 (2015) 1859–1863. [5] Yi-Hyun Park, et al., Fabrication of Li2 TiO3 pebbles using PVA-boric acid reaction for solid breeding materials, J. Nucl. Mater. 455 (2014) 106–110. [6] Yi-Hyun Park, et al., Optimization of mass-production conditions for tritium breeder pebbles based on slurry droplet wetting method, Fusion Eng. Des. 109–111 (2016) 443–447.
Please cite this article in press as: Y.-H. Park, et al., Li2 TiO3 powder synthesis by solid-state reaction and pebble fabrication for tritium breeding material, Fusion Eng. Des. (2017), http://dx.doi.org/10.1016/j.fusengdes.2017.05.015
ARTICLE IN PRESS
FUSION-9499; No. of Pages 5
Fusion Engineering and Design xxx (2017) xxx–xxx
Contents lists available at ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Li2 TiO3 powder synthesis by solid-state reaction and pebble fabrication for tritium breeding material Yi-Hyun Park ∗ , Kyung-Mi Min, Seungyon Cho, Mu-Young Ahn, Young-Min Lee National Fusion Research Institute (NFRI), Daejeon, Republic of Korea
h i g h l i g h t s • • • •
The Li2 TiO3 nano-powders were successfully synthesized by solid-state reaction process. The average particle size of synthesized Li2 TiO3 nano-powder was approximately 150 nm. The optimization of synthesis conditions for high crystalline structure and fine particle was conducted. The Li2 TiO3 pebbles with diameter of 1 mm and high uniformity were successfully fabricated by using the synthesized nano-powder.
a r t i c l e
i n f o
Article history: Received 3 October 2016 Received in revised form 27 April 2017 Accepted 4 May 2017 Available online xxx Keywords: Lithium metatitanate (Li2 TiO3 ) Nano-powder Tritium breeder Pebble Solid-state reaction
a b s t r a c t The tritium breeding materials require small particle size to reduce the diffusion distance of generated tritium in the intercrystalline. In addition, the essential resource, especially enriched Li-6, has to be recovered from the used tritium breeding material. For the hands-on operation during the recovery process, the activation level of the used breeder is strictly limited in order to reduce the impurities of long-lived radioactive nuclides in the tritium breeding material. In this study, lithium oxide (Li2 O) and titanium dioxide (TiO2 ) were used as starting materials in the synthesis of Li2 TiO3 powder. The starting materials were mixed by wet ball-milling process. The mixed powders were synthesized by heat treatment. The average particle size of synthesized Li2 TiO3 powder was approximately 150 nm. And, the long-lived radioactive nuclides, such as aluminum (Al) and cobalt (Co), were not accumulated in the synthesized Li2 TiO3 powder during the synthesis process. The Li2 TiO3 pebbles were fabricated by slurry droplet wetting method using the synthesized Li2 TiO3 nano-powder. The particle size, crush load, and porosity of fabricated Li2 TiO3 pebbles using the synthesized nano-powder were investigated. © 2017 Elsevier B.V. All rights reserved.
1. Introduction Lithium-containing ceramics compounds, such as lithium metatitanate (Li2 TiO3 ) and lithium orthosilicate (Li4 SiO4 ), are used as solid-type of tritium breeder materials for fusion breeding blankets. The tritium breeder materials require small particle size to reduce the bulk diffusion of bred tritium in the intercrystalline of breeder materials [1]. In addition, the essential resource, especially enriched Li-6, has to be recovered from the used tritium breeder materials. For the hands-on operation during the recovery process, the contents of long-lived radioactive nuclides, especially aluminum (Al) and cobalt (Co) in the tritium breeder materials are strictly limited in order to reduce the activation level of used breeder materials [2].
∗ Corresponding author. E-mail address: [email protected] (Y.-H. Park).
This study aims at the fabrication of Li2 TiO3 pebbles, which have a small particle size and low levels of the long-lived radioactive nuclides, by using solid-state reaction process [3,4]. The pebble fabrication method has been developed for application to mass-production of tritium breeder pebbles [5,6]. This method is slurry-based process and adopting to use Li2 TiO3 powder for the preparation of slurry. Therefore, the Li2 TiO3 nano-powder with high purity was synthesized by solid-state reaction process. Lithium oxide (Li2 O) and titanium dioxide (TiO2 ) were used as starting materials for the synthesis of Li2 TiO3 nano-powder. The starting materials were directly reacted at high temperature. The synthesized Li2 TiO3 nano-powder was used for the fabrication of pebbles. The effects of heat treatment temperature, heat treatment time, and molar ratio of starting materials on the synthesized Li2 TiO3 powder were investigated. In addition, the characterization of the fabricated Li2 TiO3 pebbles using synthesized nano-powder, such as diameter, grain size, porosity and crush load, were performed in this work.
http://dx.doi.org/10.1016/j.fusengdes.2017.05.015 0920-3796/© 2017 Elsevier B.V. All rights reserved.
Please cite this article in press as: Y.-H. Park, et al., Li2 TiO3 powder synthesis by solid-state reaction and pebble fabrication for tritium breeding material, Fusion Eng. Des. (2017), http://dx.doi.org/10.1016/j.fusengdes.2017.05.015
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Fig. 1. XRD patterns of synthesized Li2 TiO3 powders at different heat treatment temperatures.
2. Experiments
Microstructure of pebble surface and fractured surface after crush test was observed by SEM.
2.1. Powder synthesis 3. Results and discussion Lithium oxide (Li2 O) and titanium dioxide (TiO2 ) were used as starting materials for the synthesis of high purity Li2 TiO3 nanopowder. Two kinds of TiO2 forms, anatase and rutile, were used for the investigation of the effects on crystalline structure of synthesized Li2 TiO3 powder. The purities of Li2 O, rutile-TiO2 , and anatase-TiO2 were 99%, 99.99%, and 99.9%, respectively. The starting materials were mixed by wet ball-mill process using isopropyl alcohol as solvent during 3 h. The molar ratio of Li2 O versus TiO2 was 1.000 versus 0.890–1.000. The mixed powders were dried at 60 ◦ C in vacuum oven more than 6 h. The dried powders were heat treated in air atmosphere at 500–800 ◦ C for 2–24 h. The morphology of synthesized powder was observed by scanning electron microscope (SEM). The particle size was measured by image analysis technique through the SEM image. The crystalline structure and phase analysis were carried out by X-ray diffraction (XRD) patterns. The impurities, especially Al and Co, of starting powders and synthesized powders were determined by inductively coupled plasma optical emission spectrometry (ICP-OES).
2.2. Pebble fabrication The Li2 TiO3 pebbles were fabricated by slurry droplet wetting method, which had been developed for the fabrication of tritium breeder pebbles with highly uniformed sizes considering mass-production. The detailed procedure of pebble fabrication was presented in previous works [3,4]. The Li2 TiO3 pebbles were sintered at 1000 ◦ C for 3 h in air atmosphere. The diameters of sintered pebbles were measured by image analysis technique through the optical microscope images. The open and closed porosity of sintered pebbles were measured by Archimedes method and helium pycnometer. The crush loads of sintered pebbles were measured by screw-driven universal material testing machine, Instron 5969, at room temperature. The cross-head speed and capacity of load cell was 0.1 mm/min and 100 N, respectively. A total of 55 pebbles were tested and analyzed.
3.1. Effect of heat treatment temperature The effects of heat treatment temperature on the synthesis of Li2 TiO3 was investigated. The XRD patterns of synthesized Li2 TiO3 powders at different temperatures are shown in Fig. 1. Fig. 1(a) and (b) represents the XRD patterns of synthesized powder using rutile-TiO2 and anatase-TiO2 as starting material, respectively. In the case of using rutile-TiO2 , as shown in Fig. 1(a), the residual TiO2 was detected in the synthesized powder even though they reacted at 700 ◦ C. The amount of residual TiO2 was decreased as heat treatment temperature increases. However, the synthesized powder at 800 ◦ C included the secondary phase which was identified as Li4 Ti5 O12 . Whereas, in the case of using anatase-TiO2 , the residual TiO2 was not detected in the synthesized powder as shown in Fig. 1(b). However, unknown peaks in the synthesized powder at 650 ◦ C and 660 ◦ C were detected at 2 between 30◦ and 32◦ . The unknown phases could be avoided by increasing heat treatment temperature. When the heat treatment temperature was above 670 ◦ C, the unknown peaks in the synthesized powder disappeared. Namely, the heat treated Li2 TiO3 powder using anatase-TiO2 above 670 ◦ C was able to be synthesized with high crystalline structure. 3.2. Effect of heat treatment time The effects of heat treatment time on the crystalline structure of synthesized Li2 TiO3 powder were investigated. Fig. 2 shows the XRD patterns of synthesized powder at 700 ◦ C for different heat treatment time. Fig. 2(a) and (b) represents the XRD patterns of synthesized powders using rutile-TiO2 and anatase-TiO2 as starting material, respectively. The crystalline structure was identified from the reference pattern of monoclinic Li2 TiO3 (JCPDS No. 77–8280). According to the reference pattern, the first and second peaks of the monoclinic Li2 TiO3 are located at 2 = 18.44◦ and 2 = 43.68◦ , respectively. In other words, the peak intensity of 18.44◦ is higher than that of 43.68◦ . However, in the case of using rutile-TiO2 , the
Please cite this article in press as: Y.-H. Park, et al., Li2 TiO3 powder synthesis by solid-state reaction and pebble fabrication for tritium breeding material, Fusion Eng. Des. (2017), http://dx.doi.org/10.1016/j.fusengdes.2017.05.015
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Fig. 2. XRD patterns of synthesized Li2 TiO3 powders at different heat treatment time.
first peak intensity of a whole synthesized powder was lower than second peak intensity as shown in Fig. 2(a). It means that the heat treatment time greater than 24 h is needed for the high crystalline structure of synthesized Li2 TiO3 powder using rutile-TiO2 . On the other hand, as shown in Fig. 2(b), the first peak intensities of a whole synthesized powder using anatase-TiO2 were the same or higher than the second peak intensities. However, the unknown peaks in the heat treated powder below 6 h were also detected at 2 between 30◦ and 32◦ . The unknown phases disappeared when the heat treatment time was greater than 12 h. Therefore, the appropriate heat treatment time for high crystalline structure of synthesized Li2 TiO3 powder was 12 h.
3.3. Effect of molar ratio The effects of molar ratio of starting materials on the crystalline structure of synthesized Li2 TiO3 powder were investigated. The XRD patterns of synthesized powder using several molar ratios of Li2 O and TiO2 were represented in Fig. 3. The TiO2 was remaining in the synthesized powders using high rutile-TiO2 ratio as shown in Fig. 3(a). The residual TiO2 was able to be removed by reducing the TiO2 ratio to below 0.942. However, the intensity of first peaks was lower than that of second peaks. Whereas a whole synthesized powder using anatase-TiO2 had a high crystalline structure. In other words, the Li2 TiO3 powder with high crystalline structure was able to be synthesized at wide range of molar ratio between Li2 O and anatase-TiO2 , as shown in Fig. 3(b).
Fig. 3. XRD patterns of synthesized Li2 TiO3 powders by different molar ratio of starting materials.
Please cite this article in press as: Y.-H. Park, et al., Li2 TiO3 powder synthesis by solid-state reaction and pebble fabrication for tritium breeding material, Fusion Eng. Des. (2017), http://dx.doi.org/10.1016/j.fusengdes.2017.05.015
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Fig. 5. Optical microscope image of sintered Li2 TiO3 pebbles.
Fig. 4. Morphology of synthesized Li2 TiO3 nano-powder.
3.4. Characteristics of synthesized powder The SEM images of synthesized Li2 TiO3 powders at 700 ◦ C for 12 h with molar ratio of 0.942 are shown in Fig. 4(a) and (b). The average particle sizes of the synthesized powder using rutile-TiO2 and anatase-TiO2 were 500 nm and 150 nm, respectively. The shape of synthesized Li2 TiO3 nano-powder was spherical type. As a result of elemental analysis, Co impurity was not included in the synthesized Li2 TiO3 nano-powders using rutile-TiO2 and anatase-TiO2 as starting material. Al contents in the synthesized powder using rutile-TiO2 and anatase-TiO2 were about 30.89 ppm and 33.18 ppm, respectively. It was estimated that the Al impurity came from starting materials. The Al contents of Li2 O and rutile-TiO2 were 49.49 ppm and 13.8 ppm, respectively. However, the level of Al contents in the synthesized Li2 TiO3 nano-powder is allowable for the hands-on operation during the recovery process of essential resource, especially enriched Li-6, from used breeder materials [2]. 3.5. Properties of sintered pebbles The morphology of fabricated Li2 TiO3 pebbles using nanopowder, which is synthesized using anatase-TiO2 (Fig. 4(b)), are shown in Fig. 5. The average diameter of sintered pebbles was 1.00 mm. And they had a high uniformity and good sphericity, as shown in Fig. 5. The microstructures of surface of sintered pebble and fractured surface after crush load are shown in Fig. 6(a) and (b), respectively. The grain size of sintered pebbles was from 5 m to 40 m in spite of using synthesized Li2 TiO3 nano-powder which had an average particle size of 150 nm. Namely, the excessive and abnormal grain growth was occurred during sintering process. The main type of pores was a closed pore, which was primarily
Fig. 6. SEM images of sintered Li2 TiO3 pebbles.
formed at a triple point of grains, as shown in Fig. 6(b). The open and closed porosity of sintered pebbles were measured as 0.2% and 6.5%, respectively. The measured density of sintered pebbles was about 3.17 g/cm3 . The average crush load of sintered Li2 TiO3 pebbles was approximately 7.5 N (Fig. 7). It was relatively low because they had a lot of defects by excessive sintering, such as bumps, cracks on the surface, and so on. When the Li2 TiO3 pebbles were
Please cite this article in press as: Y.-H. Park, et al., Li2 TiO3 powder synthesis by solid-state reaction and pebble fabrication for tritium breeding material, Fusion Eng. Des. (2017), http://dx.doi.org/10.1016/j.fusengdes.2017.05.015
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150 nm. The long-lived radioactive nuclides were not detected in the synthesized Li2 TiO3 nano-powder during this synthesis process. The Li2 TiO3 pebbles with diameter of 1 mm and high uniformity were successfully fabricated using the synthesized nano-powder. However, the optimization of sintering conditions for the use of the Li2 TiO3 nano-powder will be necessary in order to improve the Li2 TiO3 pebble properties. Acknowledgments
Fig. 7. Diameter and crush load of sintered Li2 TiO3 pebbles.
sintered at 1000 ◦ C for 3 h. The sintering conditions has been optimized for using commercial Li2 TiO3 powder with particle size of 12 m. Therefore, according to the results of characteristics of sintered pebbles, the optimization of sintering conditions for using Li2 TiO3 nano-powder is strongly needed in order to improve the pebble characteristics. 4. Conclusions The effects of TiO2 forms as starting material, rutile and anatase, on the characteristics of synthesized Li2 TiO3 nano-powder were investigated. It was found that the anatase-TiO2 was suitable for synthesis of Li2 TiO3 nano-powder with high crystalline structure and fine particle. The average particle size was approximately
This work was supported by the R&D Program through the National Fusion Research Institute (NFRI) funded by the Ministry of Science, ICT and Future Planning of the Republic of Korea (NFRIIN1603). References [1] C.E. Johnson, et al., Ceramic breeder materials: status and needs, J. Nucl. Mater. 258–263 (1998) 140–148. [2] U. Fischer, H. Tsige-Tamirat, Activation characteristics of a solid breeder blanket for a fusion power demonstration reactor, J. Nucl. Mater. 307–311 (2002) 798–802. [3] Jean-Daniel Lulewicz, Nicole Roux, First results of the investigation of Li2 ZrO3 and Li2 TiO3 pebbles, Fusion Eng. Des. 39–40 (1998) 745–750. [4] Seiya Ogawa, et al., Li vaporization property of two-phase material of Li2 TiO3 and Li2 SiO3 for tritium breeder, Fusion Eng. Des. 98–99 (2015) 1859–1863. [5] Yi-Hyun Park, et al., Fabrication of Li2 TiO3 pebbles using PVA-boric acid reaction for solid breeding materials, J. Nucl. Mater. 455 (2014) 106–110. [6] Yi-Hyun Park, et al., Optimization of mass-production conditions for tritium breeder pebbles based on slurry droplet wetting method, Fusion Eng. Des. 109–111 (2016) 443–447.
Please cite this article in press as: Y.-H. Park, et al., Li2 TiO3 powder synthesis by solid-state reaction and pebble fabrication for tritium breeding material, Fusion Eng. Des. (2017), http://dx.doi.org/10.1016/j.fusengdes.2017.05.015