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Effect of TiO2 on the reduction of lithium titanate induced by H2 in the sweep gas
Fusion Engineering and Design 69 (2003) 443 /447 www.elsevier.com/locate/fusengdes
Effect of TiO2 on the reduction of lithium titanate induced by H2 in the sweep gas K. Tsuchiya a,*, C. Alvani b, H. Kawamura a, H. Yamada a, S. Casadio b, V. Contini b a
Oarai Research Establishment, Japan Atomic Energy Research Institute (JAERI), Oarai-machi, Higashi-ibaraki-gun, Ibaraki-ken 3111394, Japan b C. R. Casaccia-ENEA, Via Anguillarese, 301, 00060 Rome, Italy
Abstract Lithium titanate (Li2TiO3) has attracted the attention of many researchers because of good tritium recovery at low temperature, chemical stability, low tritium inventory, etc. In this work, the effects of TiO2 doping of Li2TiO3 on the resistance to the environmental attack in air and hydrogen reduction under Ar/0.1%H2 flow were examined. Based on the results, the TiO2 doping (from 3.7 to 30 wt%) was found to improve the resistance to the environmental attack for very long exposure times in air at room temperature. The hydrogen reaction rates of Li2TiO3 and Li4Ti5O12 were almost similar up to 800 8C and that of Li4Ti5O12 was higher in the temperature range from 800 to 950 8C. # 2003 Elsevier B.V. All rights reserved. Keywords: Fusion reactor; Lithium titanate (Li2TiO3); Environmental attack; Hydrogen reduction
1. Introduction The application of lithium titanate (Li2TiO3) pebbles (diameters from 0.2 to 2 mm) was proposed in the Japanese and European blanket designs of a fusion reactor [1]. The wet process for the fabrication of Li2TiO3 pebbles is the most advantageous from the viewpoints of mass production and reprocessing of lithium-bearing solution [2]. The grain size of Li2TiO3 pebbles fabricated by the wet process
* Corresponding author. Tel.: /81-29-264-8369; fax: /8129-264-8480. E-mail address: [email protected] (K. Tsuchiya).
was larger than that of Li2TiO3 pebbles fabricated by the extrusion /spheronization /sintering process [3,4]. Therefore, improved materials such as TiO2doped Li2TiO3 have been proposed in order to reduce the grain size. The Li2TiO3 shows good chemical stability in the air environment and good tritium release at temperatures at low as 327 8C [5]. Recent tests on the interaction with He/ 0.1%H2 purge gas showed the occurrence of reduction effect corresponding to a Li2TiO3 x formula at temperatures above 650 8C [6]. However, the chemical properties of TiO2-doped Li2TiO3 have not been evaluated so far. In this work, the effects of TiO2 doping of Li2TiO3 were examined on: (i) storage in air; and (ii) reduction under Ar/0.1%H2 sweep gas which
0920-3796/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0920-3796(03)00093-0
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K. Tsuchiya et al. / Fusion Engineering and Design 69 (2003) 443 /447
simulates the ‘reference’ purge gas for the actual fusion blanket designs.
were evaluated. The weight loss of each pellet and pebble was also evaluated after the ramp-annealing test.
2. Experiments 2.1. Materials Li2TiO3 powder was prepared with a purity of 99.9%. The particle size of the Li2TiO3 powder was in the range of 0.2 /2.3 mm with 0.6 mm in average. Titanium oxide (TiO2) powder with purity of 99.99% was also prepared and the particle size of the powder was in the region of 0.2 /2 mm. TiO2doped Li2TiO3 pellets with various TiO2 contents (8 mm diameter by 2 mm thickness) were fabricated with almost the same microstructure (density, grain size, etc.). TiO2-doped Li2TiO3 pebbles with various TiO2 contents (about 1 mm in diameter) were also fabricated by the wet process with dehydration reaction. 2.2. Procedures The micromeritics TPD /TPR (Temperature Programmed Desorption/Temperature Programmed Reduction) 2000 apparatus modified and implemented by ENEA [7] has been used in this work. TPR /TPD runs were performed by heating the specimens at constant rate (b /dT /dt) under sweep gas (Ar/0.1%H2) flow. In the first test (test run A), the weight loss and specific BET-Surface Area (BET-SA) of each pellet and pebble were evaluated after heating ramps from R.T. to 800 8C (at heating rate b /10 8C/min), then the temperature was held at 800 8C for 1 h under Ar gas flow. After the measurements, the reaction rates of each pellet and pebble were evaluated by the ramp-annealing tests performed in the range of 500/800 or 950 8C (at heating rate b /5 8C/min) under Ar/0.1%H2 flow. In the second test (test run B), the heating ramps were performed from R.T. to 500 8C under Ar/ 0.1%H2 flow using a fast heating rate (b /20 8C/ min). After heating, the ramp-annealing test was continuously performed in the range of 500/800 or 950 8C under Ar/0.1%H2 (b /5 8C/min) and hydrogen reaction rates of each pellet and pebble
3. Results 3.1. Basic properties Main characteristics of the Li2TiO3 pellets and pebbles are shown in Table 1. For the Li2TiO3 and TiO2-doped Li2TiO3 pellets, the sintering temperatures were 1076 and 960 8C, respectively. The grain size of each pellet was about 1.5 mm. The Xray diffraction patterns of Li2TiO3 and TiO2doped Li2TiO3 pellets are shown in Fig. 1. It became clear that diffraction peaks corresponding to Li2TiO3 appeared in Li2TiO3 and 5 wt% TiO2doped Li2TiO3 pellets. For the Li2TiO3 and TiO2doped Li2TiO3 pebbles, the sintering temperatures were higher and the grain size of the pebbles was larger than those of each pellet. Diffraction peaks corresponding to Li2TiO3 and Li4Ti5O12 appeared in other TiO2-doped Li2TiO3 pellets. 3.2. Hydrogen reaction The heating ramps were carried out from R.T. to 800 8C under Ar gas flow. The desorption rate during the heating ramps with each pellet and pebble are shown in Fig. 2. Two or three peaks due to the release of H2O and/or CO2 from Li2TiO3 and TiO2-doped Li2TiO3 pellets/pebbles were observed during heating. The weight loss of Li2TiO3 pellet was about 4 times larger than that of TiO2doped Li2TiO3 pellet and weight loss of TiO2doped Li2TiO3 pellet decreased with increasing TiO2 content. After the heating ramps, the BETSA of each pellet and pebble was measured. The BET-SA of pellets was between 0.60 and 0.85 m2/ g, while the BET-SA of pebbles varied between 0.20 and 0.38 m2/g. The results of hydrogen reaction rates of the pellets and the pebbles are shown in Fig. 3. The hydrogen reaction rate of Li2TiO3 increased with increasing the temperature above 750 8C and decreased with increasing temperature over 750 8C.
K. Tsuchiya et al. / Fusion Engineering and Design 69 (2003) 443 /447
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Table 1 Main characteristics of the Li2TiO3 specimens in this work Specimen No.
Shapes
Content of TiO2 doping (wt%)
Sintering temperature (8C)
Density (%T.D.)
Grain size (mm)
PLT-0 PLT-5 PLT-10 PLT-15 PLT-20 PLT-25 PLT-30 PBL-0 PBL-5 PBL-10
Pellet Pellet Pellet Pellet Pellet Pellet Pellet Pebble Pebble Pebble
0 5 10 15 20 25 30 0 3.7 7.5
1076 960 960 960 960 960 960 1235 1130 1210
82 /84 82 /84 82 /84 82 /84 82 /84 82 /84 82 /84 82.3 81.7 84.8
1.39/0.4 1.49/0.4 1.69/0.5 1.49/0.4 1.69/0.4 1.49/0.4 1.49/0.5 2 /7 2 /7 5 /30
Fig. 2. Desorption rate during heating ramps for each pellet and pebble.
Fig. 1. X-ray diffraction patterns of Li2TiO3 and TiO2-doped Li2TiO3 pellets.
After the heating ramps performed from R.T. to 500 8C under Ar/0.1%H2 flow at a fast heating rate, the ramp-annealing test was continued from 500 to 800 or 950 8C always under Ar/0.1%H2 flow, then the hydrogen reaction rates of each pellet and pebble were evaluated. A peak was observed from 500 to 690 8C in the heating ramp of Li2TiO3 pellet. On the other hand, no peak was
observed in the heating ramp of Li2TiO3 pebbles. The peak observed in the heating of the pellet seems to be due to the release of impurity gases such as CO2 from Li2TiO3 pellet. The hydrogen reaction rates of TiO2-doped Li2TiO3 pellets and pebbles increased with increasing the temperature.
4. Discussion From the results of properties, the existence Li4Ti5O12 was found and TiO2 was not found in
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K. Tsuchiya et al. / Fusion Engineering and Design 69 (2003) 443 /447
Fig. 3. Hydrogen reaction rates of TiO2-doped Li2TiO3 pellets and pebbles with various TiO2 contents.
Fig. 4. Relationship between Li4Ti5O12 content and weight loss of TiO2-doped Li2TiO3 pellets and pebbles with various TiO2 contents after the heating ramps.
TiO2-doped Li2TiO3 pellets and pebbles. In the phase diagram of the Li2O /TiO2 system [8], bLi2TiO3 and Li4Ti5O12 coexist in TiO2-doped Li2TiO3 up to 955 8C. Therefore, it is assumed that the following reaction occurs in TiO2-doped Li2TiO3 by sintering process in the fabrication. aLi2 TiO3 bTiO2 [cLi2 TiO3 dLi4 Ti5 O12
(1)
From Eq. (1), the two kinds of reactions occurred between hydrogen and oxygen. xH2 Li2 TiO3 [Li2 TiO3 x xH2 O
(2)
yH2 Li4 Ti5 O12 [Li4 Ti5 O12 y yH2 O
(3)
Relationship between Li4Ti5O12 content and weight loss of Li2TiO3 and TiO2-doped Li2TiO3 samples after the heating ramps is shown in Fig. 4. The TiO2 doping (from 3.7 to 30 wt%) was found to improve the resistance of Li2TiO3 to the environmental attack during very long exposure times in air at R.T. in the heating ramp tests. Relationship between Li4Ti5O12 content and hydrogen reaction rate of Li2TiO3 and TiO2-doped Li2TiO3 pellets and pebbles after the ramp-annealing tests is shown in Fig. 5. In this figure, the solid and dotted lines are the values calculated from content of Li4Ti5O12 in TiO2-doped Li2TiO3 and
Fig. 5. Relationship between Li4Ti5O12 content and hydrogen reaction rate of TiO2-doped Li2TiO3 pellets and pebbles with various TiO2 contents after the ramp-annealing test.
effective reaction coefficients in Eqs. (2) and (3). Diffraction peaks after the ramp-annealing test were the same as peaks before the tests in each Li2TiO3 and TiO2-doped Li2TiO3 sample. Additionally, each sample has a color after the rampannealing test that principally depends on Li4Ti5O12 content: gray /brown for un-doped mate-
K. Tsuchiya et al. / Fusion Engineering and Design 69 (2003) 443 /447
rial, violet for doped material. It seems that the intensity of the colors was also proportional to the temperature reached and to the amount of H2 interacted. It became clear that the reaction rates of Li2TiO3 and Li4Ti5O12 were almost similar up to 800 8C and the reaction rate of Li4Ti5O12 increased in the temperature range from 800 to 950 8C. In future, tritium release tests with the Li2TiO3 induced by hydrogen will be performed in order to clarify influence on hydrogen reduction of tritium release properties.
5. Conclusion The effects of TiO2 doping to Li2TiO3 was examined in atagnant air and under hydrogen reduction due to Ar/0.1%H2 flow. The TiO2doped Li2TiO3 consisted of two kinds of microstructures: Li2TiO3 and Li4Ti5O12 as the basic properties. The Li4Ti5O12 content (TiO2 doping) was found to improve the resistance to the environmental attack for very long exposure times in air at R.T. The hydrogen reaction rates of Li2TiO3 and Li4Ti5O12 were almost similar up to 800 8C while the reaction rate of Li4Ti5O12 increased with temperature from 800 to 950 8C.
447
References [1] S. Malang, Limitations on blanket performance, Fusion Eng. Des. 46 (1999) 193 /206. [2] K. Tsuchiya, M. Uchida, H. Kawamura, S. Casadio, C. Alvani, Fabrication test of Li2TiO3 pebbles by direct wet process, Pro. of the 10th International Workshop on Ceramic Breeder Blanket Interactions, Karlsruhe, Germany, 2001, pp. 93 /100. [3] J.D. Lulewicz, Advances in the pre-industrial fabrication of Li2TiO3 pebbles by the extrusion /spheronization /sintering process, Pro. of the 9th International Workshop on Ceramic Breeder Blanket Interactions, Toki, Japan, 2000, pp. 111 / 116. [4] K. Tsuchiya, H. Kawamura, K. Fuchinoue, H. Sawada, K. Watarumi, Fabrication development and preliminary characterization of Li2TiO3 pebbles by wet process, J. Nucl. Mater. 258 /263 (1998) 1985 /1990. [5] J.P. Kopasz, J.M. Miller, C.E. Johnson, Tritium release from lithium titanate, a low-activation tritium breeding material, J. Nucl. Mater. 212 /215 (1994) 927 /931. [6] C. Alvani, P.L. Carconi, S. Casadio, N. Roux, Effects of pre-treatments of Li2TiO3 pebbles on the release of tritium generated during short irradiations, Fusion Eng. Des. 58 / 59 (2001) 701 /705. [7] C. Alvani, P.L. Carconi, St. Casadio, S. Casadio, Li2TiO3 pebbles tritium release mechanism and kinetics by postirradiation ‘Temperature Programmed Desorption’ (TPD) spectroscopy, Pro. of the 10th International Workshop on Ceramic Breeder Blanket Interactions, Karlsruhe, Germany, 2001. [8] H. Kleykamp, Thermal properties of Li2TiO3 and phase equilibria in the Li /Ti /O system, Pro. of the 10th International Workshop on Ceramic Breeder Blanket Interactions, Karlsruhe, Germany, 2001.
Effect of TiO2 on the reduction of lithium titanate induced by H2 in the sweep gas K. Tsuchiya a,*, C. Alvani b, H. Kawamura a, H. Yamada a, S. Casadio b, V. Contini b a
Oarai Research Establishment, Japan Atomic Energy Research Institute (JAERI), Oarai-machi, Higashi-ibaraki-gun, Ibaraki-ken 3111394, Japan b C. R. Casaccia-ENEA, Via Anguillarese, 301, 00060 Rome, Italy
Abstract Lithium titanate (Li2TiO3) has attracted the attention of many researchers because of good tritium recovery at low temperature, chemical stability, low tritium inventory, etc. In this work, the effects of TiO2 doping of Li2TiO3 on the resistance to the environmental attack in air and hydrogen reduction under Ar/0.1%H2 flow were examined. Based on the results, the TiO2 doping (from 3.7 to 30 wt%) was found to improve the resistance to the environmental attack for very long exposure times in air at room temperature. The hydrogen reaction rates of Li2TiO3 and Li4Ti5O12 were almost similar up to 800 8C and that of Li4Ti5O12 was higher in the temperature range from 800 to 950 8C. # 2003 Elsevier B.V. All rights reserved. Keywords: Fusion reactor; Lithium titanate (Li2TiO3); Environmental attack; Hydrogen reduction
1. Introduction The application of lithium titanate (Li2TiO3) pebbles (diameters from 0.2 to 2 mm) was proposed in the Japanese and European blanket designs of a fusion reactor [1]. The wet process for the fabrication of Li2TiO3 pebbles is the most advantageous from the viewpoints of mass production and reprocessing of lithium-bearing solution [2]. The grain size of Li2TiO3 pebbles fabricated by the wet process
* Corresponding author. Tel.: /81-29-264-8369; fax: /8129-264-8480. E-mail address: [email protected] (K. Tsuchiya).
was larger than that of Li2TiO3 pebbles fabricated by the extrusion /spheronization /sintering process [3,4]. Therefore, improved materials such as TiO2doped Li2TiO3 have been proposed in order to reduce the grain size. The Li2TiO3 shows good chemical stability in the air environment and good tritium release at temperatures at low as 327 8C [5]. Recent tests on the interaction with He/ 0.1%H2 purge gas showed the occurrence of reduction effect corresponding to a Li2TiO3 x formula at temperatures above 650 8C [6]. However, the chemical properties of TiO2-doped Li2TiO3 have not been evaluated so far. In this work, the effects of TiO2 doping of Li2TiO3 were examined on: (i) storage in air; and (ii) reduction under Ar/0.1%H2 sweep gas which
0920-3796/03/$ - see front matter # 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0920-3796(03)00093-0
444
K. Tsuchiya et al. / Fusion Engineering and Design 69 (2003) 443 /447
simulates the ‘reference’ purge gas for the actual fusion blanket designs.
were evaluated. The weight loss of each pellet and pebble was also evaluated after the ramp-annealing test.
2. Experiments 2.1. Materials Li2TiO3 powder was prepared with a purity of 99.9%. The particle size of the Li2TiO3 powder was in the range of 0.2 /2.3 mm with 0.6 mm in average. Titanium oxide (TiO2) powder with purity of 99.99% was also prepared and the particle size of the powder was in the region of 0.2 /2 mm. TiO2doped Li2TiO3 pellets with various TiO2 contents (8 mm diameter by 2 mm thickness) were fabricated with almost the same microstructure (density, grain size, etc.). TiO2-doped Li2TiO3 pebbles with various TiO2 contents (about 1 mm in diameter) were also fabricated by the wet process with dehydration reaction. 2.2. Procedures The micromeritics TPD /TPR (Temperature Programmed Desorption/Temperature Programmed Reduction) 2000 apparatus modified and implemented by ENEA [7] has been used in this work. TPR /TPD runs were performed by heating the specimens at constant rate (b /dT /dt) under sweep gas (Ar/0.1%H2) flow. In the first test (test run A), the weight loss and specific BET-Surface Area (BET-SA) of each pellet and pebble were evaluated after heating ramps from R.T. to 800 8C (at heating rate b /10 8C/min), then the temperature was held at 800 8C for 1 h under Ar gas flow. After the measurements, the reaction rates of each pellet and pebble were evaluated by the ramp-annealing tests performed in the range of 500/800 or 950 8C (at heating rate b /5 8C/min) under Ar/0.1%H2 flow. In the second test (test run B), the heating ramps were performed from R.T. to 500 8C under Ar/ 0.1%H2 flow using a fast heating rate (b /20 8C/ min). After heating, the ramp-annealing test was continuously performed in the range of 500/800 or 950 8C under Ar/0.1%H2 (b /5 8C/min) and hydrogen reaction rates of each pellet and pebble
3. Results 3.1. Basic properties Main characteristics of the Li2TiO3 pellets and pebbles are shown in Table 1. For the Li2TiO3 and TiO2-doped Li2TiO3 pellets, the sintering temperatures were 1076 and 960 8C, respectively. The grain size of each pellet was about 1.5 mm. The Xray diffraction patterns of Li2TiO3 and TiO2doped Li2TiO3 pellets are shown in Fig. 1. It became clear that diffraction peaks corresponding to Li2TiO3 appeared in Li2TiO3 and 5 wt% TiO2doped Li2TiO3 pellets. For the Li2TiO3 and TiO2doped Li2TiO3 pebbles, the sintering temperatures were higher and the grain size of the pebbles was larger than those of each pellet. Diffraction peaks corresponding to Li2TiO3 and Li4Ti5O12 appeared in other TiO2-doped Li2TiO3 pellets. 3.2. Hydrogen reaction The heating ramps were carried out from R.T. to 800 8C under Ar gas flow. The desorption rate during the heating ramps with each pellet and pebble are shown in Fig. 2. Two or three peaks due to the release of H2O and/or CO2 from Li2TiO3 and TiO2-doped Li2TiO3 pellets/pebbles were observed during heating. The weight loss of Li2TiO3 pellet was about 4 times larger than that of TiO2doped Li2TiO3 pellet and weight loss of TiO2doped Li2TiO3 pellet decreased with increasing TiO2 content. After the heating ramps, the BETSA of each pellet and pebble was measured. The BET-SA of pellets was between 0.60 and 0.85 m2/ g, while the BET-SA of pebbles varied between 0.20 and 0.38 m2/g. The results of hydrogen reaction rates of the pellets and the pebbles are shown in Fig. 3. The hydrogen reaction rate of Li2TiO3 increased with increasing the temperature above 750 8C and decreased with increasing temperature over 750 8C.
K. Tsuchiya et al. / Fusion Engineering and Design 69 (2003) 443 /447
445
Table 1 Main characteristics of the Li2TiO3 specimens in this work Specimen No.
Shapes
Content of TiO2 doping (wt%)
Sintering temperature (8C)
Density (%T.D.)
Grain size (mm)
PLT-0 PLT-5 PLT-10 PLT-15 PLT-20 PLT-25 PLT-30 PBL-0 PBL-5 PBL-10
Pellet Pellet Pellet Pellet Pellet Pellet Pellet Pebble Pebble Pebble
0 5 10 15 20 25 30 0 3.7 7.5
1076 960 960 960 960 960 960 1235 1130 1210
82 /84 82 /84 82 /84 82 /84 82 /84 82 /84 82 /84 82.3 81.7 84.8
1.39/0.4 1.49/0.4 1.69/0.5 1.49/0.4 1.69/0.4 1.49/0.4 1.49/0.5 2 /7 2 /7 5 /30
Fig. 2. Desorption rate during heating ramps for each pellet and pebble.
Fig. 1. X-ray diffraction patterns of Li2TiO3 and TiO2-doped Li2TiO3 pellets.
After the heating ramps performed from R.T. to 500 8C under Ar/0.1%H2 flow at a fast heating rate, the ramp-annealing test was continued from 500 to 800 or 950 8C always under Ar/0.1%H2 flow, then the hydrogen reaction rates of each pellet and pebble were evaluated. A peak was observed from 500 to 690 8C in the heating ramp of Li2TiO3 pellet. On the other hand, no peak was
observed in the heating ramp of Li2TiO3 pebbles. The peak observed in the heating of the pellet seems to be due to the release of impurity gases such as CO2 from Li2TiO3 pellet. The hydrogen reaction rates of TiO2-doped Li2TiO3 pellets and pebbles increased with increasing the temperature.
4. Discussion From the results of properties, the existence Li4Ti5O12 was found and TiO2 was not found in
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K. Tsuchiya et al. / Fusion Engineering and Design 69 (2003) 443 /447
Fig. 3. Hydrogen reaction rates of TiO2-doped Li2TiO3 pellets and pebbles with various TiO2 contents.
Fig. 4. Relationship between Li4Ti5O12 content and weight loss of TiO2-doped Li2TiO3 pellets and pebbles with various TiO2 contents after the heating ramps.
TiO2-doped Li2TiO3 pellets and pebbles. In the phase diagram of the Li2O /TiO2 system [8], bLi2TiO3 and Li4Ti5O12 coexist in TiO2-doped Li2TiO3 up to 955 8C. Therefore, it is assumed that the following reaction occurs in TiO2-doped Li2TiO3 by sintering process in the fabrication. aLi2 TiO3 bTiO2 [cLi2 TiO3 dLi4 Ti5 O12
(1)
From Eq. (1), the two kinds of reactions occurred between hydrogen and oxygen. xH2 Li2 TiO3 [Li2 TiO3 x xH2 O
(2)
yH2 Li4 Ti5 O12 [Li4 Ti5 O12 y yH2 O
(3)
Relationship between Li4Ti5O12 content and weight loss of Li2TiO3 and TiO2-doped Li2TiO3 samples after the heating ramps is shown in Fig. 4. The TiO2 doping (from 3.7 to 30 wt%) was found to improve the resistance of Li2TiO3 to the environmental attack during very long exposure times in air at R.T. in the heating ramp tests. Relationship between Li4Ti5O12 content and hydrogen reaction rate of Li2TiO3 and TiO2-doped Li2TiO3 pellets and pebbles after the ramp-annealing tests is shown in Fig. 5. In this figure, the solid and dotted lines are the values calculated from content of Li4Ti5O12 in TiO2-doped Li2TiO3 and
Fig. 5. Relationship between Li4Ti5O12 content and hydrogen reaction rate of TiO2-doped Li2TiO3 pellets and pebbles with various TiO2 contents after the ramp-annealing test.
effective reaction coefficients in Eqs. (2) and (3). Diffraction peaks after the ramp-annealing test were the same as peaks before the tests in each Li2TiO3 and TiO2-doped Li2TiO3 sample. Additionally, each sample has a color after the rampannealing test that principally depends on Li4Ti5O12 content: gray /brown for un-doped mate-
K. Tsuchiya et al. / Fusion Engineering and Design 69 (2003) 443 /447
rial, violet for doped material. It seems that the intensity of the colors was also proportional to the temperature reached and to the amount of H2 interacted. It became clear that the reaction rates of Li2TiO3 and Li4Ti5O12 were almost similar up to 800 8C and the reaction rate of Li4Ti5O12 increased in the temperature range from 800 to 950 8C. In future, tritium release tests with the Li2TiO3 induced by hydrogen will be performed in order to clarify influence on hydrogen reduction of tritium release properties.
5. Conclusion The effects of TiO2 doping to Li2TiO3 was examined in atagnant air and under hydrogen reduction due to Ar/0.1%H2 flow. The TiO2doped Li2TiO3 consisted of two kinds of microstructures: Li2TiO3 and Li4Ti5O12 as the basic properties. The Li4Ti5O12 content (TiO2 doping) was found to improve the resistance to the environmental attack for very long exposure times in air at R.T. The hydrogen reaction rates of Li2TiO3 and Li4Ti5O12 were almost similar up to 800 8C while the reaction rate of Li4Ti5O12 increased with temperature from 800 to 950 8C.
447
References [1] S. Malang, Limitations on blanket performance, Fusion Eng. Des. 46 (1999) 193 /206. [2] K. Tsuchiya, M. Uchida, H. Kawamura, S. Casadio, C. Alvani, Fabrication test of Li2TiO3 pebbles by direct wet process, Pro. of the 10th International Workshop on Ceramic Breeder Blanket Interactions, Karlsruhe, Germany, 2001, pp. 93 /100. [3] J.D. Lulewicz, Advances in the pre-industrial fabrication of Li2TiO3 pebbles by the extrusion /spheronization /sintering process, Pro. of the 9th International Workshop on Ceramic Breeder Blanket Interactions, Toki, Japan, 2000, pp. 111 / 116. [4] K. Tsuchiya, H. Kawamura, K. Fuchinoue, H. Sawada, K. Watarumi, Fabrication development and preliminary characterization of Li2TiO3 pebbles by wet process, J. Nucl. Mater. 258 /263 (1998) 1985 /1990. [5] J.P. Kopasz, J.M. Miller, C.E. Johnson, Tritium release from lithium titanate, a low-activation tritium breeding material, J. Nucl. Mater. 212 /215 (1994) 927 /931. [6] C. Alvani, P.L. Carconi, S. Casadio, N. Roux, Effects of pre-treatments of Li2TiO3 pebbles on the release of tritium generated during short irradiations, Fusion Eng. Des. 58 / 59 (2001) 701 /705. [7] C. Alvani, P.L. Carconi, St. Casadio, S. Casadio, Li2TiO3 pebbles tritium release mechanism and kinetics by postirradiation ‘Temperature Programmed Desorption’ (TPD) spectroscopy, Pro. of the 10th International Workshop on Ceramic Breeder Blanket Interactions, Karlsruhe, Germany, 2001. [8] H. Kleykamp, Thermal properties of Li2TiO3 and phase equilibria in the Li /Ti /O system, Pro. of the 10th International Workshop on Ceramic Breeder Blanket Interactions, Karlsruhe, Germany, 2001.