- Email: [email protected]
Trial fabrication of tritium breeders for fusion blanket with lithium recovered from seawater
Fusion Engineering and Design 39 – 40 (1998) 731 – 737
Trial fabrication of tritium breeders for fusion blanket with lithium recovered from seawater Kunihiko Tsuchiya *, Hiroshi Kawamura Oarai Research Establishment, JAERI, Oarai-machi, Higashi-Ibaraki-gun, Ibaraki-ken 311 -13, Japan
Abstract Lithium ceramics have been considered as one of the candidates for the fabrication of tritium breeders for fusion reactors. As a part of the study program for fusion blanket development, fabrication techniques for tritium breeders which are made of lithium ceramics have been investigated and the characteristics of tritium breeders fabricated by several fabrication methods are estimated. On the other hand, lithium deposits in ore are very poor in Japan. Hence, lithium recovered from seawater should be effectively utilized for tritium breeders. In this study, g-LiAlO2 pellets were fabricated by solid–solid reactions between Al2O3 and Li2CO3 recovered from seawater or ore, and the characteristics of two kinds of g-LiAlO2 mentioned above, i.e. fabrication, physical and thermal properties, were estimated. © 1998 Elsevier Science S.A. All rights reserved.
1. Introduction Lithium ceramics have received considerable attention as tritium breeders for fusion reactors [1,2]. Candidate ceramic breeder materials considered at present include Li2O [3], LiAlO2 [4], Li2ZrO3 [5], Li2TiO3 [6] and Li4SiO4 [7]. Li2O is attractive for obtaining a high tritium breeding ratio because of its high lithium density [8]. LiAlO2, Li2ZrO3 and Li4SiO4, because of their better thermochemical stability, are more reliable in terms of lithium mass transfer and compatibility with other blanket materials, such as the neutron multiplier and structural materials [9]. As a part of the study program for fusion blanket development, fabrication techniques for * Corresponding author. Tel.: + 81 29 2648369; fax: + 81 29 2648480; e-mail: [email protected]
tritium breeders which are made of lithium ceramics have been investigated and the characteristics of tritium breeders fabricated by several fabrication methods are estimated. Also, development of reprocessing technology to recover lithium for tritium breeders has been proposed from the viewpoint of the effective use of resources [10]. On the other hand, lithium deposits in ore are very poor in Japan. One of the possible future sources of lithium is seawater and the world supply contains a total amount of about 2.5×1011 tons at a low concentration (170 ppb). Various methods have been studied for the recovery of lithium from seawater, brine, and geothermal water. These can be classified into three groups: adsorption (ion-exchange) [11], solvent extraction [12], and co-precipitation [13]. Recovery of lithium from seawater is about 10 kg year − 1. On the other hand, if the use of
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K. Tsuchiya, H. Kawamura / Fusion Engineering and Design 39–40 (1998) 731–737
thermal pollution of atomic power plants (100 kW) is possible for lithium recovery, lithium can be recovered from seawater at a rate of up to 350 t for 1 year [14]. Hence, lithium recovered from seawater should be effectively utilized for the fabrication of tritium breeders. In this study, g-LiAlO2 pellets were fabricated by solid–solid reactions between Al2O3 and Li2CO3 powders fabricated with the lithium recovered from seawater or ore, and the characteristics of two kinds of g-LiAlO2 mentioned above, i.e. fabrication, physical and thermal properties, were estimated.
2. Experimental
2.1. Starting powders Two kinds of Li2CO3 powders fabricated with the lithium recovered from seawater or ore were prepared as the starting powders in this study. The Li2CO3 powder fabricated with the lithium recovered from seawater (Li2CO3/seawater) was supplied by Shikoku National Industrial Research Institute (SNIRI). The extraction method of the lithium is reported by Ooi et al. and Miyai et al. [15,16]. The chemical compositions of Li2CO3 powders fabricated with the lithium recovered from seawater and ore are shown in Table 1. Two kinds of Li2CO3 powders were 99.9%, respectively. However, the main impurities of the Li2CO3/seawater were as follows: Na, 210; Ca, 140; Fe, 50 (in ppm). The content of these elements in the Li2CO3/seawater was higher than that in Li2CO3 powders fabricated with the lithium recovered from ore (Li2CO3/ore). On the other hand, a-Al2O3 powder was prepared. The purity and particle size of a-Al2O3 powder were 99.9% and 2 – 3 mm, respectively. The main impurities of a-Al2O3 powder were as follows: Ca, 3; Fe, 100; Mg, 3; Ni, 40; Si, 200 (in ppm).
2.2. Fabrication tests of g-LiAlO2 In this study, the g-LiAlO2 was selected as the
candidate tritium breeding material because it is easy to handle. Two kinds of g-LiAlO2 were prepared by the solid–solid reactions between a-Al2O3 and each Li2CO3 powder fabricated with the lithium recovered from seawater or ore. A flow chart of the fabrication of g-LiAlO2 pellets is shown in Fig. 1. The true densities of two kinds of Li2CO3 powder and a-Al2O3 powder were measured by pycnometer. After decomposition, the true densities of the two kinds of LiAlO2 powder before sintering were measured and the chemical forms of the LiAlO2 powders before sintering were analyzed by X-ray diffraction (XRD). Fabrication properties of g-LiAlO2 were performed by density measurement and scanning electron microscopy (SEM) observation. From cold-pressing and sintering tests, the pressure and sintering temperature were decided for fabrication of g-LiAlO2 pellets with about 82% T.D. The dimension of the fabricated pellets was f 19× 3.7 mm.
2.3. Characterization of g-LiAlO2 The characteristics of the two kinds of gLiAlO2 pellets were evaluated. Basic properties of Table 1 Chemical compositions of Li2CO3 powders fabricated with the lithium recovered from seawater and ore Element
Li2CO3 (%) Si (ppm) Al (ppm) Ca (ppm) Na (ppm) K (ppm) Fe (ppm) Ni (ppm) Cr (ppm) Mg (ppm) Pb (ppm) Cu (ppm) H2O (%) a
Starting powdera Li2CO3/seawater
Li2CO3/ore
99.9 — — 140 210 10 50 — — 10 — — —
\99.9 8 — 2 2 2 1 — — B1 B0.5 0.2 0.01
Starting powder for fabrications of g-LiAlO2 pellets.
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3. Results and discussions
3.1. Fabricating properties
Fig. 1. Flow chart on fabrication of g-LiAlO2 pellets.
two kinds of g-LiAlO2 pellets, such as density, grain size, impurities and chemical form, were measured. The density of the pellets was measured by mercury porosimetry. Impurity levels were measured by inductively coupled plasma-based (ICP) spectroscopic analyzer. The moisture absorption properties of a-Al2O3 powder and LiAlO2 powders before/after sintering were evaluated. Each powder was exposed at room temperature for 168 h (7 days) in air atmosphere. The amount of moisture absorption was measured in vacuum by thermogravimetry/differential thermal analyzer (TG/DTA). Specific heat and thermal diffusivity of two kinds of g-LiAlO2 pellets were measured by the laser flash method. The degree of vacuum was less than 2× 10 − 4 Pa. The thermal diffusivity and specific heat of these pellets were obtained by measurement of elevated temperature on the pellets using an infrared ray temperature sensor and a thermocouple. Thermal conductivity was calculated from these measurement values and the density of these pellets.
The results of true densities of a-Al2O3 powder and the two kinds of Li2CO3 powder as starting powders, and the LiAlO2 powders before sintering, are shown in Table 2. The true densities of a-Al2O3 powder, Li2CO3/seawater and Li2CO3/ ore agreed well with the reference values [17]. On the other hand, the true density of the two kinds of LiAlO2 powder before sintering was about 3.0 g cm − 3, and LiAlO2 powders of a- and b-phases were mixed after decomposition. A pressure of 530 kg cm − 2 was selected from the cold-pressing tests, and sintering tests were performed. The sintering temperature dependence on the density of g-LiAlO2 is shown in Fig. 2. From this figure, the density of g-LiAlO2/seawater and g-LiAlO2/ore increased with increasing sintering temperature, and sintering properties were not different from each Li2CO3 powder. When the sintering temperature was 1000°C, the density of g-LiAlO2 pellets was about 82% T.D. This density was obtained by measurements of the dimension and weight of the pellets. The XRD patterns of LiAlO2 powders using Li2CO3 powders fabricated with the lithium recovered from seawater are shown in Fig. 3. Diffraction peaks corresponding to a-LiAlO2 and g-LiAlO2 appeared in the LiAlO2 powder before sintering. On the other hand, diffraction peaks corresponding only to g-LiAlO2 appeared in the LiAlO2 powder after sintering. The XRD patterns of LiAlO2 powders using Li2CO3 powders fabricated with lithium recovered from ore were similar to those described above. In this section, it is shown that the sintering properties in fabrication were not different from each Li2CO3 powder, and the sintering temperature (1000°C) was decided.
3.2. Basic properties The results of density, porosity and specific surface of g-LiAlO2 pellets measured by mercury porosimetry is shown in Table 3. From the results, the g-LiAlO2 pellet using Li2CO3 powders
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Table 2 Results of true densities of a-Al2O3 powder and two kinds of Li2CO3 powders as starting powders, and the LiAlO2 powders before sintering Powder
Starting powders
LiAlO2 powders before sintering
a
Experimental results (g cm−3)
Densitya (g cm−3)
Al2O3 powder Li2CO3 recovered from seawater Li2CO3 recovered from ore LiAlO2 powders with seawater
3.86 2.09
a-Al2O3: 3.90 Li2CO3: 2.10
2.09 2.98
Li2CO3: 2.10 a-LiAlO2: 3.40, g-LiAlO2: 2.55
LiAlO2 powders with ore
3.02
a-LiAlO2: 3.40, g-LiAlO2: 2.55
Reference values [17].
fabricated with the lithium recovered from seawater (g-LiAlO2/seawater) was 84.7% T.D. and the specific surface area was 0.67 m2 g − 1. The gLiAlO2 pellet using Li2CO3 powders fabricated with the lithium recovered from ore (g-LiAlO2/ ore) was 86.7% T.D. and the specific surface area was 1.25 m2 g − 1. The specific surface of gLiAlO2/seawater was smaller than that of gLiAlO2/ore. The chemical compositions of g-LiAlO2 pellets using Li2CO3 powders fabricated with the lithium recovered from seawater and ore are shown in Table 4. Na, Ca and Fe in Li2CO3/seawater were 210, 140 and 50 ppm, respectively. However, Na, Ca and Fe decreased 99, 55 and 19 ppm in the
Fig. 2. Sintering temperature dependence on density of gLiAlO2 pellets.
g-LiAlO2/seawater, respectively. On the other hand, Na, Ca and Fe in the Li2CO3/ore were 2, 2 and 1 ppm, respectively. Na, Ca and Fe increased 12, 9 and 12 ppm in g-LiAlO2/ore, respectively. A SEM photograph of a cross-section of gLiAlO2 pellet with Li2CO3 powder using Li2CO3 powders fabricated with the lithium recovered from seawater is shown in Fig. 4. From this photograph, the grain size of g-LiAlO2/seawater was about 2 mm. On the other hand, the grain size of g-LiAlO2/ore was also about 2 mm and the grain size of g-LiAlO2/seawater is almost the same as that of g-LiAlO2/ore.
Fig. 3. X-ray diffraction patterns of LiAlO2 powders using Li2CO3 powders fabricated with the lithium recovered from seawater.
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Table 3 Results of density, porosity and specific surface of g-LiAlO2 pellets measured by mercury porosimetry Properties
Pellets g-LiAlO2/seawater
Density (%T.D.) 84.7 Porosity (%) 10.2 Specific surface (m2 g−1) 0.67
g-LiAlO2/ore
86.7 12.3 1.25
The moisture absorption properties of gLiAlO2 powders after sintering were evaluated. From the results, the moisture absorption rates of g-LiAlO2 powders (after sintering) using Li2CO3 powders fabricated with the lithium recovered from seawater and ore were 5.0 and 2.9%, respectively. The amount of moisture absorption of the g-LiAlO2 powders using Li2CO3 powders fabricated with the lithium recovered from seawater was larger than that of the gLiAlO2 powders using Li2CO3 powders fabricated with the lithium recovered from ore. It seems that impurities (NaO, CaO, MgO, etc.) influence these results. In the future, the effects of impurities shall be investigated.
Table 4 Chemical compositions of g-LiAlO2 pellets using Li2CO3 powders fabricated with the lithium recovered from seawater and ore Elements
Ca (ppm) Na (ppm) Fe (ppm) Ni (ppm) Cr (ppm) Mg (ppm) Cu (ppm) Mn (ppm) Co (ppm) B (ppm)
Fig. 4. SEM photograph of cross-section of g-LiAlO2 pellet with Li2CO3 powder using Li2CO3 powders fabricated with the lithium recovered from seawater.
3.3. Thermal properties Thermal properties such as specific heat and thermal conductivity were measured by the laser flash method in the temperature range 20– 700°C. The temperature dependence on specific heat of g-LiAlO2 pellet using Li2CO3 powders fabricated with the lithium recovered from seawater and ore is shown in Fig. 5. These experimental data agreed with the values measured by Brandt and Schultz [18]. From the results, specific heats of g-LiAlO2/seawater and g-LiAlO2/ore are given as follows: g-LiAlO2/seawater:
Pellets g-LiAlO2/seawater
g-LiAlO2/ore
99 55 19 15 4 7 0.7 0.7 0.4 18
9 12 12 15 5 6 0.3 0.4 1 3
Fig. 5. Temperature dependence on specific heat of g-LiAlO2 pellet using Li2CO3 powders fabricated with the lithium recovered from seawater and ore.
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the values calculated as density of 84% T.D. by the equation which was reported by Hollenberg and Baker [19]. The thermal conductivity of gLiAlO2/seawater approximately agreed with the calculated values. From these results, it is shown that the thermal properties of the g-LiAlO2 pellet using Li2CO3 powders fabricated with the lithium recovered from seawater are almost the same as those of the g-LiAlO2 pellet using Li2CO3 powders fabricated with the lithium recovered from ore. Fig. 6. Temperature dependence on thermal conductivity of g-LiAlO2 pellet using Li2CO3 powders fabricated with the lithium recovered from seawater and ore.
cp (J g − 1 K − 1) =1.41+6.7 ×10 − 4T − 3.9 ×104T − 2
(1)
g-LiAlO2/ore cp (J g − 1 K − 1) =1.63+8.7 ×10 − 4T − 4.0 ×104T − 2
(2)
The measured specific heat of g-LiAlO2/seawater approximately agreed with that of g-LiAlO2/ore. Thermal diffusivity, a, was obtained by the half-time method. The thermal diffusivity of each g-LiAlO2 pellet decreased with increasing measurement temperature. The thermal diffusivity of g-LiAlO2/seawater was about 3.5×10 − 6 m2 s − 1 at room temperature, falling to about 9.8 × 10 − 7 m2 s − 1 at the highest temperature measured. On the other hand, the thermal diffusivity of gLiAlO2/ore has almost the same value as that of g-LiAlO2/seawater. The values of thermal conductivity are calculated by the following relation: k= acpr
4. Conclusion Two kinds of g-LiAlO2 were fabricated by solid–solid reactions between a-Al2O3 and each Li2CO3 powder fabricated with the lithium recovered from seawater or ore. When the pressure in cold-pressing was 530 kg cm − 2 and the sintering temperature was 1000°C, the density of each g-LiAlO2 pellet was about 82% T.D. The basic properties of g-LiAlO2/seawater, such as density, grain size, chemical form, etc. were similar to those of g-LiAlO2/ore, and the impurities in gLiAlO2 pellets had little influence on the basic properties of g-LiAlO2. On the other hand, the amount of moisture absorption of the g-LiAlO2 powders using Li2CO3 powders fabricated with the lithium recovered from seawater was larger than that of the g-LiAlO2 powders using Li2CO3 powders fabricated with the lithium recovered from ore. The thermal properties of g-LiAlO2/ seawater are almost the same as those of gLiAlO2/ore. From these results, the prospects are bright for fabrication of tritium breeders using Li2CO3 fabricated with the lithium recovered from seawater.
(3) −1
−1
where k is thermal conductivity in W m K , −3 and r density in g m . The temperature dependence on thermal conductivity of a g-LiAlO2 pellet with Li2CO3 powder using Li2CO3 powders fabricated with the lithium recovered from seawater and ore is shown in Fig. 6. In Fig. 6, the solid line shows
Acknowledgements We are grateful to Dr T. Niiho (Oarai Research Establishment, JAERI), Dr S. Katoh, Dr K. Ooi and Dr Y. Miyai (Shikoku National Industrial Research Institute) for their kind support.
K. Tsuchiya, H. Kawamura / Fusion Engineering and Design 39–40 (1998) 731–737
References [1] C.E. Johnson, K.R. Kummerer, E. Roth, Ceramic breeder materials, J. Nucl. Mater. 155/157 (1988) 188 – 201. [2] C.E. Johnson, Research and development status of ceramic breeder materials, J. Nucl. Mater. 179/181 (1991) 42 – 46. [3] M.S. Ortman, E.M. Larsen, Preparation, characterization, and melting point of high-purity lithium oxide, J. Am. Cer. Soc. 66 (1983) 645–648. [4] C. Alvani, S. Casadio, L. Lorenzini, G. Brambilla, Fabrication of porous LiAlO2 ceramic breeder material, Fusion Technol. 10 (1986) 106–112. [5] J.W. Kammeyer, O.J. Whittemore, Reactive lithium zirconate, Adv. Ceram. 25 (1989) 117–121. [6] N. Roux, J. Avon, A. Floreancig, J. Mougin, B.R. Asneur, S. Ravel, Low temperature tritium releasing ceramics as potential materials for the ITER breeding blanket, Proc. 4th Int. Workshop Ceramic Breeder Blanket Interactions, 1995, pp. 452–468. [7] D. Vollath, H. Wedemeyer, Techniques for synthesizing lithium silicates and lithium aluminates, Adv. Ceram. 25 (1989) 93 –103. [8] D.L. Smith, Evaluation of candidate blanket materials for fusion reactor blanket applications, J. Nucl. Mater. 122/ 123 (1984) 51–65.
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[9] P. Groner, W. Scifritz, Ceramic lithium compounds for solid breeder concepts for fusion reactors, Nucl. Technol./ Fusion 5 (1984) 169 – 177. [10] K. Tsuchiya, H. Kawamura, M. Saito, K. Tatenuma, M. Kainose, Lithium reprocessing technology for ceramic breeders, J. Nucl. Mater. 219 (1996) 246 – 249. [11] Y. Miyai, K. Ooi, S. Katoh, Preparation and ion-exchange properties of ion-sieve manganese oxide based on MgMn2O4, J. Colloid Interface Sci. 130 (1989) 535–541. [12] A.E. Torma, G.G. Gabra, Metall. 32 (1978) 581. [13] H. Wada, T. Kitamura, K. Ooi, S. Katoh, J. Min. Met. Inst. Jpn. 99 (1983) 585. [14] K. Ooi, Y. Miyai, S. Katoh, M. Abe, Recovery of lithium from seawater, Bull. Soc. Sea Water Sci. Jpn. 42 (1989) 219 – 227. [15] K. Ooi, Y. Miyai, S. Katoh, Recovery of lithium from seawater by manganese oxide adsorbent, Separation Sci. Technol. 21 (1986) 755 – 766. [16] Y. Miyai, K. Ooi, S. Katoh, Recovery of lithium from seawater using a new type of ion-sieve adsorbent based on MgMn2O4, Separation Sci. Technol. 23 (1988) 179 –191. [17] S. Mizushima, et al., Encyclopaedia Chimica, printed in Japan, 1961. [18] R. Brandt, B. Schultz, Specific heat of some Li-compounds, J. Nucl. Mater. 152 (1988) 178 – 181. [19] G.W. Hollenberg, D.E. Baker, Thermal properties of lithium ceramics for fusion applications, HEDL-SA-2674FP, 1982.
Trial fabrication of tritium breeders for fusion blanket with lithium recovered from seawater Kunihiko Tsuchiya *, Hiroshi Kawamura Oarai Research Establishment, JAERI, Oarai-machi, Higashi-Ibaraki-gun, Ibaraki-ken 311 -13, Japan
Abstract Lithium ceramics have been considered as one of the candidates for the fabrication of tritium breeders for fusion reactors. As a part of the study program for fusion blanket development, fabrication techniques for tritium breeders which are made of lithium ceramics have been investigated and the characteristics of tritium breeders fabricated by several fabrication methods are estimated. On the other hand, lithium deposits in ore are very poor in Japan. Hence, lithium recovered from seawater should be effectively utilized for tritium breeders. In this study, g-LiAlO2 pellets were fabricated by solid–solid reactions between Al2O3 and Li2CO3 recovered from seawater or ore, and the characteristics of two kinds of g-LiAlO2 mentioned above, i.e. fabrication, physical and thermal properties, were estimated. © 1998 Elsevier Science S.A. All rights reserved.
1. Introduction Lithium ceramics have received considerable attention as tritium breeders for fusion reactors [1,2]. Candidate ceramic breeder materials considered at present include Li2O [3], LiAlO2 [4], Li2ZrO3 [5], Li2TiO3 [6] and Li4SiO4 [7]. Li2O is attractive for obtaining a high tritium breeding ratio because of its high lithium density [8]. LiAlO2, Li2ZrO3 and Li4SiO4, because of their better thermochemical stability, are more reliable in terms of lithium mass transfer and compatibility with other blanket materials, such as the neutron multiplier and structural materials [9]. As a part of the study program for fusion blanket development, fabrication techniques for * Corresponding author. Tel.: + 81 29 2648369; fax: + 81 29 2648480; e-mail: [email protected]
tritium breeders which are made of lithium ceramics have been investigated and the characteristics of tritium breeders fabricated by several fabrication methods are estimated. Also, development of reprocessing technology to recover lithium for tritium breeders has been proposed from the viewpoint of the effective use of resources [10]. On the other hand, lithium deposits in ore are very poor in Japan. One of the possible future sources of lithium is seawater and the world supply contains a total amount of about 2.5×1011 tons at a low concentration (170 ppb). Various methods have been studied for the recovery of lithium from seawater, brine, and geothermal water. These can be classified into three groups: adsorption (ion-exchange) [11], solvent extraction [12], and co-precipitation [13]. Recovery of lithium from seawater is about 10 kg year − 1. On the other hand, if the use of
0920-3796/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved. PII S0920-3796(98)00178-1
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K. Tsuchiya, H. Kawamura / Fusion Engineering and Design 39–40 (1998) 731–737
thermal pollution of atomic power plants (100 kW) is possible for lithium recovery, lithium can be recovered from seawater at a rate of up to 350 t for 1 year [14]. Hence, lithium recovered from seawater should be effectively utilized for the fabrication of tritium breeders. In this study, g-LiAlO2 pellets were fabricated by solid–solid reactions between Al2O3 and Li2CO3 powders fabricated with the lithium recovered from seawater or ore, and the characteristics of two kinds of g-LiAlO2 mentioned above, i.e. fabrication, physical and thermal properties, were estimated.
2. Experimental
2.1. Starting powders Two kinds of Li2CO3 powders fabricated with the lithium recovered from seawater or ore were prepared as the starting powders in this study. The Li2CO3 powder fabricated with the lithium recovered from seawater (Li2CO3/seawater) was supplied by Shikoku National Industrial Research Institute (SNIRI). The extraction method of the lithium is reported by Ooi et al. and Miyai et al. [15,16]. The chemical compositions of Li2CO3 powders fabricated with the lithium recovered from seawater and ore are shown in Table 1. Two kinds of Li2CO3 powders were 99.9%, respectively. However, the main impurities of the Li2CO3/seawater were as follows: Na, 210; Ca, 140; Fe, 50 (in ppm). The content of these elements in the Li2CO3/seawater was higher than that in Li2CO3 powders fabricated with the lithium recovered from ore (Li2CO3/ore). On the other hand, a-Al2O3 powder was prepared. The purity and particle size of a-Al2O3 powder were 99.9% and 2 – 3 mm, respectively. The main impurities of a-Al2O3 powder were as follows: Ca, 3; Fe, 100; Mg, 3; Ni, 40; Si, 200 (in ppm).
2.2. Fabrication tests of g-LiAlO2 In this study, the g-LiAlO2 was selected as the
candidate tritium breeding material because it is easy to handle. Two kinds of g-LiAlO2 were prepared by the solid–solid reactions between a-Al2O3 and each Li2CO3 powder fabricated with the lithium recovered from seawater or ore. A flow chart of the fabrication of g-LiAlO2 pellets is shown in Fig. 1. The true densities of two kinds of Li2CO3 powder and a-Al2O3 powder were measured by pycnometer. After decomposition, the true densities of the two kinds of LiAlO2 powder before sintering were measured and the chemical forms of the LiAlO2 powders before sintering were analyzed by X-ray diffraction (XRD). Fabrication properties of g-LiAlO2 were performed by density measurement and scanning electron microscopy (SEM) observation. From cold-pressing and sintering tests, the pressure and sintering temperature were decided for fabrication of g-LiAlO2 pellets with about 82% T.D. The dimension of the fabricated pellets was f 19× 3.7 mm.
2.3. Characterization of g-LiAlO2 The characteristics of the two kinds of gLiAlO2 pellets were evaluated. Basic properties of Table 1 Chemical compositions of Li2CO3 powders fabricated with the lithium recovered from seawater and ore Element
Li2CO3 (%) Si (ppm) Al (ppm) Ca (ppm) Na (ppm) K (ppm) Fe (ppm) Ni (ppm) Cr (ppm) Mg (ppm) Pb (ppm) Cu (ppm) H2O (%) a
Starting powdera Li2CO3/seawater
Li2CO3/ore
99.9 — — 140 210 10 50 — — 10 — — —
\99.9 8 — 2 2 2 1 — — B1 B0.5 0.2 0.01
Starting powder for fabrications of g-LiAlO2 pellets.
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3. Results and discussions
3.1. Fabricating properties
Fig. 1. Flow chart on fabrication of g-LiAlO2 pellets.
two kinds of g-LiAlO2 pellets, such as density, grain size, impurities and chemical form, were measured. The density of the pellets was measured by mercury porosimetry. Impurity levels were measured by inductively coupled plasma-based (ICP) spectroscopic analyzer. The moisture absorption properties of a-Al2O3 powder and LiAlO2 powders before/after sintering were evaluated. Each powder was exposed at room temperature for 168 h (7 days) in air atmosphere. The amount of moisture absorption was measured in vacuum by thermogravimetry/differential thermal analyzer (TG/DTA). Specific heat and thermal diffusivity of two kinds of g-LiAlO2 pellets were measured by the laser flash method. The degree of vacuum was less than 2× 10 − 4 Pa. The thermal diffusivity and specific heat of these pellets were obtained by measurement of elevated temperature on the pellets using an infrared ray temperature sensor and a thermocouple. Thermal conductivity was calculated from these measurement values and the density of these pellets.
The results of true densities of a-Al2O3 powder and the two kinds of Li2CO3 powder as starting powders, and the LiAlO2 powders before sintering, are shown in Table 2. The true densities of a-Al2O3 powder, Li2CO3/seawater and Li2CO3/ ore agreed well with the reference values [17]. On the other hand, the true density of the two kinds of LiAlO2 powder before sintering was about 3.0 g cm − 3, and LiAlO2 powders of a- and b-phases were mixed after decomposition. A pressure of 530 kg cm − 2 was selected from the cold-pressing tests, and sintering tests were performed. The sintering temperature dependence on the density of g-LiAlO2 is shown in Fig. 2. From this figure, the density of g-LiAlO2/seawater and g-LiAlO2/ore increased with increasing sintering temperature, and sintering properties were not different from each Li2CO3 powder. When the sintering temperature was 1000°C, the density of g-LiAlO2 pellets was about 82% T.D. This density was obtained by measurements of the dimension and weight of the pellets. The XRD patterns of LiAlO2 powders using Li2CO3 powders fabricated with the lithium recovered from seawater are shown in Fig. 3. Diffraction peaks corresponding to a-LiAlO2 and g-LiAlO2 appeared in the LiAlO2 powder before sintering. On the other hand, diffraction peaks corresponding only to g-LiAlO2 appeared in the LiAlO2 powder after sintering. The XRD patterns of LiAlO2 powders using Li2CO3 powders fabricated with lithium recovered from ore were similar to those described above. In this section, it is shown that the sintering properties in fabrication were not different from each Li2CO3 powder, and the sintering temperature (1000°C) was decided.
3.2. Basic properties The results of density, porosity and specific surface of g-LiAlO2 pellets measured by mercury porosimetry is shown in Table 3. From the results, the g-LiAlO2 pellet using Li2CO3 powders
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Table 2 Results of true densities of a-Al2O3 powder and two kinds of Li2CO3 powders as starting powders, and the LiAlO2 powders before sintering Powder
Starting powders
LiAlO2 powders before sintering
a
Experimental results (g cm−3)
Densitya (g cm−3)
Al2O3 powder Li2CO3 recovered from seawater Li2CO3 recovered from ore LiAlO2 powders with seawater
3.86 2.09
a-Al2O3: 3.90 Li2CO3: 2.10
2.09 2.98
Li2CO3: 2.10 a-LiAlO2: 3.40, g-LiAlO2: 2.55
LiAlO2 powders with ore
3.02
a-LiAlO2: 3.40, g-LiAlO2: 2.55
Reference values [17].
fabricated with the lithium recovered from seawater (g-LiAlO2/seawater) was 84.7% T.D. and the specific surface area was 0.67 m2 g − 1. The gLiAlO2 pellet using Li2CO3 powders fabricated with the lithium recovered from ore (g-LiAlO2/ ore) was 86.7% T.D. and the specific surface area was 1.25 m2 g − 1. The specific surface of gLiAlO2/seawater was smaller than that of gLiAlO2/ore. The chemical compositions of g-LiAlO2 pellets using Li2CO3 powders fabricated with the lithium recovered from seawater and ore are shown in Table 4. Na, Ca and Fe in Li2CO3/seawater were 210, 140 and 50 ppm, respectively. However, Na, Ca and Fe decreased 99, 55 and 19 ppm in the
Fig. 2. Sintering temperature dependence on density of gLiAlO2 pellets.
g-LiAlO2/seawater, respectively. On the other hand, Na, Ca and Fe in the Li2CO3/ore were 2, 2 and 1 ppm, respectively. Na, Ca and Fe increased 12, 9 and 12 ppm in g-LiAlO2/ore, respectively. A SEM photograph of a cross-section of gLiAlO2 pellet with Li2CO3 powder using Li2CO3 powders fabricated with the lithium recovered from seawater is shown in Fig. 4. From this photograph, the grain size of g-LiAlO2/seawater was about 2 mm. On the other hand, the grain size of g-LiAlO2/ore was also about 2 mm and the grain size of g-LiAlO2/seawater is almost the same as that of g-LiAlO2/ore.
Fig. 3. X-ray diffraction patterns of LiAlO2 powders using Li2CO3 powders fabricated with the lithium recovered from seawater.
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Table 3 Results of density, porosity and specific surface of g-LiAlO2 pellets measured by mercury porosimetry Properties
Pellets g-LiAlO2/seawater
Density (%T.D.) 84.7 Porosity (%) 10.2 Specific surface (m2 g−1) 0.67
g-LiAlO2/ore
86.7 12.3 1.25
The moisture absorption properties of gLiAlO2 powders after sintering were evaluated. From the results, the moisture absorption rates of g-LiAlO2 powders (after sintering) using Li2CO3 powders fabricated with the lithium recovered from seawater and ore were 5.0 and 2.9%, respectively. The amount of moisture absorption of the g-LiAlO2 powders using Li2CO3 powders fabricated with the lithium recovered from seawater was larger than that of the gLiAlO2 powders using Li2CO3 powders fabricated with the lithium recovered from ore. It seems that impurities (NaO, CaO, MgO, etc.) influence these results. In the future, the effects of impurities shall be investigated.
Table 4 Chemical compositions of g-LiAlO2 pellets using Li2CO3 powders fabricated with the lithium recovered from seawater and ore Elements
Ca (ppm) Na (ppm) Fe (ppm) Ni (ppm) Cr (ppm) Mg (ppm) Cu (ppm) Mn (ppm) Co (ppm) B (ppm)
Fig. 4. SEM photograph of cross-section of g-LiAlO2 pellet with Li2CO3 powder using Li2CO3 powders fabricated with the lithium recovered from seawater.
3.3. Thermal properties Thermal properties such as specific heat and thermal conductivity were measured by the laser flash method in the temperature range 20– 700°C. The temperature dependence on specific heat of g-LiAlO2 pellet using Li2CO3 powders fabricated with the lithium recovered from seawater and ore is shown in Fig. 5. These experimental data agreed with the values measured by Brandt and Schultz [18]. From the results, specific heats of g-LiAlO2/seawater and g-LiAlO2/ore are given as follows: g-LiAlO2/seawater:
Pellets g-LiAlO2/seawater
g-LiAlO2/ore
99 55 19 15 4 7 0.7 0.7 0.4 18
9 12 12 15 5 6 0.3 0.4 1 3
Fig. 5. Temperature dependence on specific heat of g-LiAlO2 pellet using Li2CO3 powders fabricated with the lithium recovered from seawater and ore.
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the values calculated as density of 84% T.D. by the equation which was reported by Hollenberg and Baker [19]. The thermal conductivity of gLiAlO2/seawater approximately agreed with the calculated values. From these results, it is shown that the thermal properties of the g-LiAlO2 pellet using Li2CO3 powders fabricated with the lithium recovered from seawater are almost the same as those of the g-LiAlO2 pellet using Li2CO3 powders fabricated with the lithium recovered from ore. Fig. 6. Temperature dependence on thermal conductivity of g-LiAlO2 pellet using Li2CO3 powders fabricated with the lithium recovered from seawater and ore.
cp (J g − 1 K − 1) =1.41+6.7 ×10 − 4T − 3.9 ×104T − 2
(1)
g-LiAlO2/ore cp (J g − 1 K − 1) =1.63+8.7 ×10 − 4T − 4.0 ×104T − 2
(2)
The measured specific heat of g-LiAlO2/seawater approximately agreed with that of g-LiAlO2/ore. Thermal diffusivity, a, was obtained by the half-time method. The thermal diffusivity of each g-LiAlO2 pellet decreased with increasing measurement temperature. The thermal diffusivity of g-LiAlO2/seawater was about 3.5×10 − 6 m2 s − 1 at room temperature, falling to about 9.8 × 10 − 7 m2 s − 1 at the highest temperature measured. On the other hand, the thermal diffusivity of gLiAlO2/ore has almost the same value as that of g-LiAlO2/seawater. The values of thermal conductivity are calculated by the following relation: k= acpr
4. Conclusion Two kinds of g-LiAlO2 were fabricated by solid–solid reactions between a-Al2O3 and each Li2CO3 powder fabricated with the lithium recovered from seawater or ore. When the pressure in cold-pressing was 530 kg cm − 2 and the sintering temperature was 1000°C, the density of each g-LiAlO2 pellet was about 82% T.D. The basic properties of g-LiAlO2/seawater, such as density, grain size, chemical form, etc. were similar to those of g-LiAlO2/ore, and the impurities in gLiAlO2 pellets had little influence on the basic properties of g-LiAlO2. On the other hand, the amount of moisture absorption of the g-LiAlO2 powders using Li2CO3 powders fabricated with the lithium recovered from seawater was larger than that of the g-LiAlO2 powders using Li2CO3 powders fabricated with the lithium recovered from ore. The thermal properties of g-LiAlO2/ seawater are almost the same as those of gLiAlO2/ore. From these results, the prospects are bright for fabrication of tritium breeders using Li2CO3 fabricated with the lithium recovered from seawater.
(3) −1
−1
where k is thermal conductivity in W m K , −3 and r density in g m . The temperature dependence on thermal conductivity of a g-LiAlO2 pellet with Li2CO3 powder using Li2CO3 powders fabricated with the lithium recovered from seawater and ore is shown in Fig. 6. In Fig. 6, the solid line shows
Acknowledgements We are grateful to Dr T. Niiho (Oarai Research Establishment, JAERI), Dr S. Katoh, Dr K. Ooi and Dr Y. Miyai (Shikoku National Industrial Research Institute) for their kind support.
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