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Effects of gelation and sintering conditions on granulation of Li2TiO3 pebbles from Li–Ti complex solution
Fusion Engineering and Design 75–79 (2005) 877–880
Effects of gelation and sintering conditions on granulation of Li2TiO3 pebbles from Li–Ti complex solution K. Tsuchiya a,∗ , H. Kawamura a , S. Casadio b , C. Alvani b a
Naka Fusion Research Establishment (Oarai-site), Japan Atomic Energy Research Institute (JAERI), 3607 Shinbori, Narita-Cho, Oarai-Machi, Higashi-ibaraki-Gun, Ibaraki-Ken 311-1394, Japan b ENEA, C.R. Casaccia, Via Anguillarese, 301, 00060 Rome, Italy Available online 27 July 2005
Abstract Application of Li2 TiO3 pebbles was proposed in the Japanese and European blanket design of a fusion reactor. The wet process and direct sol–gel methods are most advantageous from viewpoints of low-cost mass fabrication, reprocessing of lithium-bearing solution and removal of radioactive isotopes. Previously, the target density (80–85% T.D.) of Li2 TiO3 pebbles was achieved in the preliminary fabrication test; however, the grain size of Li2 TiO3 pebbles was larger than 5 m and low sphericity. Therefore, the fabrication tests of Li2 TiO3 pebbles by the direct-wet process were continued, focusing the effects on dissolving process of Li2 TiO3 , dropping of the solution into coagulant and drying/calcinating and sintering processes of the droplet for high sphericity and decreasing the cracks of Li2 TiO3 pebble surface. © 2005 Elsevier B.V. All rights reserved. Keywords: Fusion reactor; Breeding materials; Fabrication
1. Introduction The application of Li2 TiO3 pebbles (diameter: 0.2–2 mm, density: 80–85% T.D., grain size: <5 m) was proposed in the Japanese and European blanket design of a fusion reactor [1,2]. The wet process and direct sol–gel methods are most advantageous from viewpoints of low-cost mass fabrication, reprocessing of lithium-bearing solution and removal of radioactive isotopes. The Li2 TiO3 pebbles were fabricated success∗ Corresponding author. Tel.: +81 29 266 7369; fax: +81 29 266 7481. E-mail address: [email protected] (K. Tsuchiya).
0920-3796/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.fusengdes.2005.06.063
fully by the indirect-wet process [3,4]. However, there was a disadvantage on reprocessing from used breeder pebbles because Li2 CO3 had to be recovered from the Li2 TiO3 solution for the preparation treatment of this process. On the other hand, the direct-wet process that Li2 TiO3 pebbles were fabricated from the liquid in which used Li2 TiO3 pebbles were dissolved was proposed [5]. This wet process is also advantageous from the viewpoint of effective use of lithium-6. Preliminary and improvement fabrication tests of Li2 TiO3 pebbles by the direct-wet process was carried out to survey its feasibility and the Li2 TiO3 pebbles were successfully fabricated from the liquid in which Li2 TiO3 were dissolved [6,7]. However, the grain size of Li2 TiO3
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K. Tsuchiya et al. / Fusion Engineering and Design 75–79 (2005) 877–880
pebbles was larger than 5 m and the sphericity low. In this study, the fabrication tests of Li2 TiO3 pebbles by the direct-wet process were continued, focusing the effects on dissolving process of Li2 TiO3 , dropping of the solution into coagulant, drying/calcinating and sintering processes of the droplet for high sphericity and decreasing the cracks of Li2 TiO3 pebble surface.
each solution. In this examination, the weight changes of the gel-spheres by heating were measured by the thermogravimetry and differential thermal analyzer (TG/DTA). The Li2 TiO3 spheres were also sintered in an electric furnace at 1000 ◦ C in air. Microstructure and crystal structures were examined by scanning electron microscopy (SEM) and X-ray diffractometry, respectively.
2. Experiments
3. Results and discussion
The present fabrication tests were performed to survey the effects of the parameters for each step of the process (see Fig. 1). The Li2 TiO3 powder with a purity of 99.9% was fabricated by Soekawa Chemical Co. Ltd. Crystal structure of the powder was examined by X-ray diffractometry (XRD). The first examination was conducted in order to decide the conditions for dissolving Li2 TiO3 powder under stirring. The 1st run was tried using the solution of Li2 TiO3 with 30% H2 O2 solvent. The 2nd run was made by using the solution of Li2 TiO3 with 30% H2 O2 + C6 H8 O7 solvent. Li2 TiO3 powder was dissolved in both runs at 60–100 ◦ C. Each solution was condensed by heating and the condensed solution was dropped into acetone. The second examination was conducted in order to decide the drying and calcinating conditions of gel-spheres fabricated by
The dissolving of Li2 TiO3 powder in 30% H2 O2 was performed in a water bath controlled with stirring and Li2 TiO3 was almost fully dissolved in 30% H2 O2 . The dissolving time was over 4 h in the case of solid/liquid ratio of 8 g:100 cm3 . The reaction was highly exothermic and the color of the solution was yellow. After dissolving, the Li2 TiO3 solution was set on hot plate and evaporation and enrichment of the Li2 TiO3 solution was carried out. White deposit was generated in the solution and the liquid including the precipitate was condensed by heating. Content of Li2 TiO3 powder were 14 wt%, 19 wt% and 23 wt%, respectively. The droplet became gradually a gel state in acetone and the gel-spheres with 1–2 mm diameter were obtained in this test. From the result of TG/DTA, the gelspheres were dried in two steps, such as 90 ◦ C × 3 h and 110 ◦ C × 1 h and calcinated in three steps, such as 170 ◦ C × 1 h, 185 ◦ C × 1 h and 200 ◦ C × 0.5 h in air because decreasing the crack of spheres in the drying process. After this process, the spheres were sintered at 1000 ◦ C for 4 h. The photograph of sintered Li2 TiO3 pebbles is shown in Fig. 2. The crystal phase of the Li2 TiO3 pebbles was observed by Xray diffraction and only X-ray peaks of Li2 TiO3 were detected. Density of the Li2 TiO3 pebbles was about 80% T.D. In the 2nd run, Li2 TiO3 powder (8 g) was dissolved in the mixture 30% H2 O2 (100 cm3 ) and C6 H8 O7 (20 g). Also, in this case, the Li2 TiO3 powder was almost completely dissolved in the solvent. The reaction was not exothermic and the color of the solution was red-orange. The Li2 TiO3 powder was dissolved when pH was about 6. The Li2 TiO3 solution was set on the hot plate and evaporation and enrichment of the Li2 TiO3 solution was two times. Viscosity of Li2 TiO3 solution was increased by evaporating water, but the
Fig. 1. Flow chart of fabrication process of Li2 TiO3 pebbles with Li–Ti complex solution.
K. Tsuchiya et al. / Fusion Engineering and Design 75–79 (2005) 877–880
879
Fig. 3. The result of TG/DTA analysis of gel-spheres.
ity were fabricated at 25 ◦ C. It seems that the aging temperature in acetone depended on density of yellow powder because dehydration reaction increased with increasing the aging temperature. For decision of the calcinating condition, the weight loss of gel-spheres was measured by the TG/DTA. The result of TG/DTA analysis of gel-spheres is shown in Fig. 3. Four peaks corresponding to the weight loss caused by releasing H2 O, H2 O2 , CO, CO2 and O2 from gel-spheres were observed with increasing the temperature in the Fig. 2. The photograph of sintered Li2 TiO3 pebbles.
deposit did not appear in the solution. The dissolving formation of the lithium salt of the citric complex of the dinuclear group peroxo–titanium(IV) is shown in Eq. (1) and its stabile dissolution by dissociation in lithium cation (Li+ ) and in tridentate chelate peroxo–Ti(IV) complex anions is shown in Eq. (2). 2Li2 TiO3 + 2H2 O2 + 2C6 H8 O7 ·H2 O → Li4 [Ti2 O5 (C6 H4 O7 )2 ] + 8H2 O
(1)
Li4 [Ti2 O5 (C6 H4 O7 )2 ] + xH2 O → 4Li+ (aq.) + [Ti2 O5 (C6 H4 O7 )2 xOH]4−x (aq.) + xH+ (aq.)
(2)
After evaporation, the condensed liquid was dropped in acetone and gel-spheres were generated after 1 h. The aging temperature examined were 5 ◦ C and 25 ◦ C for 2 h. The gel-spheres with high spheric-
Fig. 4. X-ray diffraction pattern of yellow powder and white powder calcinaed at 600 ◦ C.
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K. Tsuchiya et al. / Fusion Engineering and Design 75–79 (2005) 877–880
DTA/DT. Significant weight loss of gel-spheres took place up to 600 ◦ C and total weight loss was about two-thirds of weight of yellow powder. Weight loss was not observed above 600 ◦ C because of complete reaction of the gel-spheres. Fig. 4 shows the X-ray diffraction pattern of yellow and white powders calcinated at 600 ◦ C. Heating of the gel-spheres was slowly carried out in the calcinating process and the Li2 TiO3 spheres were sintered at 1000 ◦ C in air after the calcination. The crystal phase of the pebbles was observed by XRD and only X-ray diffraction peaks of Li2 TiO3 were observed. However, the Li2 TiO3 pebbles were porous because of high weight loss and density was very low. Density improvement tests of the Li2 TiO3 pebbles will be performed with the solution of Li2 TiO3 powder in 30% H2 O2 + C6 H8 O7 in future work.
4. Conclusion The fabrication test of Li2 TiO3 pebbles was performed with Li–Ti complex solution and the following can be concluded: (1) 100% Li2 TiO3 powder could be dissolved by increasing the holding time at temperatures higher than 60 ◦ C. In the evaporation and enrichment of the solution, deposit in Li2 TiO3 solution was decreased by applying C6 H8 O7 as solvent. (2) The gel-spheres were maintained by dropping the Li2 TiO3 condensed solution liquid in acetone. Gelspheres with higher sphericity were fabricated at 25 ◦ C when the solution of Li2 TiO3 powder in 30% H2 O2 + C6 H8 O7 was used.
(3) Li2 TiO3 pebbles with density about 80% T.D. after sintering were obtained in the solution with 30% H2 O2 . On the other hand, the Li2 TiO3 pebbles produced with 30% H2 O2 + C6 H8 O7 solution were too porous. Future works will aim at improving density by the optimization of the process parameter.
References [1] M. Enoeda, S. Sato, T. Hatano, Y. Yanagi, S. Kikuchi, T. Kuroda, Y. Ohara, Evolution of Japanese design of DEMO solid breeder blanket, in: Proceedings of the Ninth International Workshop on Ceramic Breeder Blanket Interactions, Toki, Japan, 27–29 September 2000, pp. 27–38. [2] S. Malang, Limitations on blanket performance, Fusion Eng. Des. 46 (1999) 193–206. [3] K. Tsuchiya, H. Kawamura, K. Fuchinoue, H. Sawada, K. Watarumi, Fabrication development and preliminary characterization of Li2 TiO3 pebbles by wet process, J. Nucl. Mater. 258–263 (1998) 1985–1990. [4] K. Tsuchiya, H. Kawamura, Development of wet process with substitution reaction for the mass production of Li2 TiO3 pebbles, J. Nucl. Mater. 283–287 (2000) 1380–1384. [5] C. Alivani, P.L. Carconi, S. Casadio, V. Contini, A. Dibartolomeo, F. Pierdominici, A. Deptula, S. Lagos, C.A. Nannetti, Lithium titanate pebbles reprocessing by wet chemistry, J. Nucl. Mater. 289 (2001) 303–307. [6] K. Tsuchiya, M. Uchida, H. Kawamura, C. Alvani, S. Casadio, Fabrication tests of Li2 TiO3 pebbles by direct wet process, in: Proceedings of the 10th International Workshop on Ceramic Breeder Blanket Interactions, Karlsruhe, Germany, 2001. [7] K. Tsuchiya, H. Kawamura, M. Uchida, S. Casadio, C. Alvani, Y. Ito, Improvement of sintered density of Li2 TiO3 pebbles fabricated by direct-wet process, Fusion Eng. Des. 69 (2003) 449– 453.
Effects of gelation and sintering conditions on granulation of Li2TiO3 pebbles from Li–Ti complex solution K. Tsuchiya a,∗ , H. Kawamura a , S. Casadio b , C. Alvani b a
Naka Fusion Research Establishment (Oarai-site), Japan Atomic Energy Research Institute (JAERI), 3607 Shinbori, Narita-Cho, Oarai-Machi, Higashi-ibaraki-Gun, Ibaraki-Ken 311-1394, Japan b ENEA, C.R. Casaccia, Via Anguillarese, 301, 00060 Rome, Italy Available online 27 July 2005
Abstract Application of Li2 TiO3 pebbles was proposed in the Japanese and European blanket design of a fusion reactor. The wet process and direct sol–gel methods are most advantageous from viewpoints of low-cost mass fabrication, reprocessing of lithium-bearing solution and removal of radioactive isotopes. Previously, the target density (80–85% T.D.) of Li2 TiO3 pebbles was achieved in the preliminary fabrication test; however, the grain size of Li2 TiO3 pebbles was larger than 5 m and low sphericity. Therefore, the fabrication tests of Li2 TiO3 pebbles by the direct-wet process were continued, focusing the effects on dissolving process of Li2 TiO3 , dropping of the solution into coagulant and drying/calcinating and sintering processes of the droplet for high sphericity and decreasing the cracks of Li2 TiO3 pebble surface. © 2005 Elsevier B.V. All rights reserved. Keywords: Fusion reactor; Breeding materials; Fabrication
1. Introduction The application of Li2 TiO3 pebbles (diameter: 0.2–2 mm, density: 80–85% T.D., grain size: <5 m) was proposed in the Japanese and European blanket design of a fusion reactor [1,2]. The wet process and direct sol–gel methods are most advantageous from viewpoints of low-cost mass fabrication, reprocessing of lithium-bearing solution and removal of radioactive isotopes. The Li2 TiO3 pebbles were fabricated success∗ Corresponding author. Tel.: +81 29 266 7369; fax: +81 29 266 7481. E-mail address: [email protected] (K. Tsuchiya).
0920-3796/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.fusengdes.2005.06.063
fully by the indirect-wet process [3,4]. However, there was a disadvantage on reprocessing from used breeder pebbles because Li2 CO3 had to be recovered from the Li2 TiO3 solution for the preparation treatment of this process. On the other hand, the direct-wet process that Li2 TiO3 pebbles were fabricated from the liquid in which used Li2 TiO3 pebbles were dissolved was proposed [5]. This wet process is also advantageous from the viewpoint of effective use of lithium-6. Preliminary and improvement fabrication tests of Li2 TiO3 pebbles by the direct-wet process was carried out to survey its feasibility and the Li2 TiO3 pebbles were successfully fabricated from the liquid in which Li2 TiO3 were dissolved [6,7]. However, the grain size of Li2 TiO3
878
K. Tsuchiya et al. / Fusion Engineering and Design 75–79 (2005) 877–880
pebbles was larger than 5 m and the sphericity low. In this study, the fabrication tests of Li2 TiO3 pebbles by the direct-wet process were continued, focusing the effects on dissolving process of Li2 TiO3 , dropping of the solution into coagulant, drying/calcinating and sintering processes of the droplet for high sphericity and decreasing the cracks of Li2 TiO3 pebble surface.
each solution. In this examination, the weight changes of the gel-spheres by heating were measured by the thermogravimetry and differential thermal analyzer (TG/DTA). The Li2 TiO3 spheres were also sintered in an electric furnace at 1000 ◦ C in air. Microstructure and crystal structures were examined by scanning electron microscopy (SEM) and X-ray diffractometry, respectively.
2. Experiments
3. Results and discussion
The present fabrication tests were performed to survey the effects of the parameters for each step of the process (see Fig. 1). The Li2 TiO3 powder with a purity of 99.9% was fabricated by Soekawa Chemical Co. Ltd. Crystal structure of the powder was examined by X-ray diffractometry (XRD). The first examination was conducted in order to decide the conditions for dissolving Li2 TiO3 powder under stirring. The 1st run was tried using the solution of Li2 TiO3 with 30% H2 O2 solvent. The 2nd run was made by using the solution of Li2 TiO3 with 30% H2 O2 + C6 H8 O7 solvent. Li2 TiO3 powder was dissolved in both runs at 60–100 ◦ C. Each solution was condensed by heating and the condensed solution was dropped into acetone. The second examination was conducted in order to decide the drying and calcinating conditions of gel-spheres fabricated by
The dissolving of Li2 TiO3 powder in 30% H2 O2 was performed in a water bath controlled with stirring and Li2 TiO3 was almost fully dissolved in 30% H2 O2 . The dissolving time was over 4 h in the case of solid/liquid ratio of 8 g:100 cm3 . The reaction was highly exothermic and the color of the solution was yellow. After dissolving, the Li2 TiO3 solution was set on hot plate and evaporation and enrichment of the Li2 TiO3 solution was carried out. White deposit was generated in the solution and the liquid including the precipitate was condensed by heating. Content of Li2 TiO3 powder were 14 wt%, 19 wt% and 23 wt%, respectively. The droplet became gradually a gel state in acetone and the gel-spheres with 1–2 mm diameter were obtained in this test. From the result of TG/DTA, the gelspheres were dried in two steps, such as 90 ◦ C × 3 h and 110 ◦ C × 1 h and calcinated in three steps, such as 170 ◦ C × 1 h, 185 ◦ C × 1 h and 200 ◦ C × 0.5 h in air because decreasing the crack of spheres in the drying process. After this process, the spheres were sintered at 1000 ◦ C for 4 h. The photograph of sintered Li2 TiO3 pebbles is shown in Fig. 2. The crystal phase of the Li2 TiO3 pebbles was observed by Xray diffraction and only X-ray peaks of Li2 TiO3 were detected. Density of the Li2 TiO3 pebbles was about 80% T.D. In the 2nd run, Li2 TiO3 powder (8 g) was dissolved in the mixture 30% H2 O2 (100 cm3 ) and C6 H8 O7 (20 g). Also, in this case, the Li2 TiO3 powder was almost completely dissolved in the solvent. The reaction was not exothermic and the color of the solution was red-orange. The Li2 TiO3 powder was dissolved when pH was about 6. The Li2 TiO3 solution was set on the hot plate and evaporation and enrichment of the Li2 TiO3 solution was two times. Viscosity of Li2 TiO3 solution was increased by evaporating water, but the
Fig. 1. Flow chart of fabrication process of Li2 TiO3 pebbles with Li–Ti complex solution.
K. Tsuchiya et al. / Fusion Engineering and Design 75–79 (2005) 877–880
879
Fig. 3. The result of TG/DTA analysis of gel-spheres.
ity were fabricated at 25 ◦ C. It seems that the aging temperature in acetone depended on density of yellow powder because dehydration reaction increased with increasing the aging temperature. For decision of the calcinating condition, the weight loss of gel-spheres was measured by the TG/DTA. The result of TG/DTA analysis of gel-spheres is shown in Fig. 3. Four peaks corresponding to the weight loss caused by releasing H2 O, H2 O2 , CO, CO2 and O2 from gel-spheres were observed with increasing the temperature in the Fig. 2. The photograph of sintered Li2 TiO3 pebbles.
deposit did not appear in the solution. The dissolving formation of the lithium salt of the citric complex of the dinuclear group peroxo–titanium(IV) is shown in Eq. (1) and its stabile dissolution by dissociation in lithium cation (Li+ ) and in tridentate chelate peroxo–Ti(IV) complex anions is shown in Eq. (2). 2Li2 TiO3 + 2H2 O2 + 2C6 H8 O7 ·H2 O → Li4 [Ti2 O5 (C6 H4 O7 )2 ] + 8H2 O
(1)
Li4 [Ti2 O5 (C6 H4 O7 )2 ] + xH2 O → 4Li+ (aq.) + [Ti2 O5 (C6 H4 O7 )2 xOH]4−x (aq.) + xH+ (aq.)
(2)
After evaporation, the condensed liquid was dropped in acetone and gel-spheres were generated after 1 h. The aging temperature examined were 5 ◦ C and 25 ◦ C for 2 h. The gel-spheres with high spheric-
Fig. 4. X-ray diffraction pattern of yellow powder and white powder calcinaed at 600 ◦ C.
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K. Tsuchiya et al. / Fusion Engineering and Design 75–79 (2005) 877–880
DTA/DT. Significant weight loss of gel-spheres took place up to 600 ◦ C and total weight loss was about two-thirds of weight of yellow powder. Weight loss was not observed above 600 ◦ C because of complete reaction of the gel-spheres. Fig. 4 shows the X-ray diffraction pattern of yellow and white powders calcinated at 600 ◦ C. Heating of the gel-spheres was slowly carried out in the calcinating process and the Li2 TiO3 spheres were sintered at 1000 ◦ C in air after the calcination. The crystal phase of the pebbles was observed by XRD and only X-ray diffraction peaks of Li2 TiO3 were observed. However, the Li2 TiO3 pebbles were porous because of high weight loss and density was very low. Density improvement tests of the Li2 TiO3 pebbles will be performed with the solution of Li2 TiO3 powder in 30% H2 O2 + C6 H8 O7 in future work.
4. Conclusion The fabrication test of Li2 TiO3 pebbles was performed with Li–Ti complex solution and the following can be concluded: (1) 100% Li2 TiO3 powder could be dissolved by increasing the holding time at temperatures higher than 60 ◦ C. In the evaporation and enrichment of the solution, deposit in Li2 TiO3 solution was decreased by applying C6 H8 O7 as solvent. (2) The gel-spheres were maintained by dropping the Li2 TiO3 condensed solution liquid in acetone. Gelspheres with higher sphericity were fabricated at 25 ◦ C when the solution of Li2 TiO3 powder in 30% H2 O2 + C6 H8 O7 was used.
(3) Li2 TiO3 pebbles with density about 80% T.D. after sintering were obtained in the solution with 30% H2 O2 . On the other hand, the Li2 TiO3 pebbles produced with 30% H2 O2 + C6 H8 O7 solution were too porous. Future works will aim at improving density by the optimization of the process parameter.
References [1] M. Enoeda, S. Sato, T. Hatano, Y. Yanagi, S. Kikuchi, T. Kuroda, Y. Ohara, Evolution of Japanese design of DEMO solid breeder blanket, in: Proceedings of the Ninth International Workshop on Ceramic Breeder Blanket Interactions, Toki, Japan, 27–29 September 2000, pp. 27–38. [2] S. Malang, Limitations on blanket performance, Fusion Eng. Des. 46 (1999) 193–206. [3] K. Tsuchiya, H. Kawamura, K. Fuchinoue, H. Sawada, K. Watarumi, Fabrication development and preliminary characterization of Li2 TiO3 pebbles by wet process, J. Nucl. Mater. 258–263 (1998) 1985–1990. [4] K. Tsuchiya, H. Kawamura, Development of wet process with substitution reaction for the mass production of Li2 TiO3 pebbles, J. Nucl. Mater. 283–287 (2000) 1380–1384. [5] C. Alivani, P.L. Carconi, S. Casadio, V. Contini, A. Dibartolomeo, F. Pierdominici, A. Deptula, S. Lagos, C.A. Nannetti, Lithium titanate pebbles reprocessing by wet chemistry, J. Nucl. Mater. 289 (2001) 303–307. [6] K. Tsuchiya, M. Uchida, H. Kawamura, C. Alvani, S. Casadio, Fabrication tests of Li2 TiO3 pebbles by direct wet process, in: Proceedings of the 10th International Workshop on Ceramic Breeder Blanket Interactions, Karlsruhe, Germany, 2001. [7] K. Tsuchiya, H. Kawamura, M. Uchida, S. Casadio, C. Alvani, Y. Ito, Improvement of sintered density of Li2 TiO3 pebbles fabricated by direct-wet process, Fusion Eng. Des. 69 (2003) 449– 453.