Abstract
In La-Mg-Ni system hydrogen storage alloys, which have been attracting attention as a promising negative electrode material for Ni-MH secondary batteries, there are many phases with a variously layered stacking structure. When subjected to annealing at high temperature, the composition of these alloys becomes inhomogeneous due to the volatilization of Mg. It is therefore difficult to prepare a single phase by the normal annealing procedure. We carried out high-temperature annealing processing in which we controlled the Mg vapor pressure of La 4MgNi 19 alloy using a temperature-gradient furnace. By controlling the Mg vapor pressure under the sealing atmosphere, we successfully obtained homogeneous La 4MgNi 19. We prepared a P Mg-T diagram of the phases formed for La 4MgNi 19 composition, and found the optimum annealing conditions for the La 4MgNi 19 phase. The optimum annealing conditions obtained were between T= 1123 K, P Mg = 0.4 kPa and T = 1223 K, P Mg = 2 kPa. However, we found the coexistence of 3R-type and 2H-type structures, which are polytypes of La 4MgNi 19. The lattice constants of the 3R type were a = 0.5031 nm, c = 4.826 nm, and those of the 2H type were a = 0.5032 nm, c = 3.216 nm. The hydrogen storage characteristics of the annealed alloy were obtained by measuring the PCT curves at 333 K. The PCT curves showed an almost flat plateau, P H2 = 0.1 MPa, H/M= 1.1, 1.5 mass%H 2, and good cycle characteristics. It was confirmed that the dehydrogenated alloy retained the same structure but an expansion of 1 to 2% was observed in the c-axis.
| Original language | English |
|---|---|
| Pages (from-to) | 158-161 |
| Number of pages | 4 |
| Journal | Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals |
| Volume | 70 |
| Issue number | 2 |
| DOIs | |
| Publication status | Published - Feb 1 2006 |
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All Science Journal Classification (ASJC) codes
- Condensed Matter Physics
- Mechanics of Materials
- Metals and Alloys
- Materials Chemistry
Cite this
Annealing conditions with Mg vapor-pressure control and hydrogen storage characteristic of la 4MgNi 19 hydrogen storage alloy. / Hayakawa, Hiroshi; Enoki, Hirotoshi; Akiba, Etsuo.
In: Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals, Vol. 70, No. 2, 01.02.2006, p. 158-161.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Annealing conditions with Mg vapor-pressure control and hydrogen storage characteristic of la 4MgNi 19 hydrogen storage alloy
AU - Hayakawa, Hiroshi
AU - Enoki, Hirotoshi
AU - Akiba, Etsuo
PY - 2006/2/1
Y1 - 2006/2/1
N2 - In La-Mg-Ni system hydrogen storage alloys, which have been attracting attention as a promising negative electrode material for Ni-MH secondary batteries, there are many phases with a variously layered stacking structure. When subjected to annealing at high temperature, the composition of these alloys becomes inhomogeneous due to the volatilization of Mg. It is therefore difficult to prepare a single phase by the normal annealing procedure. We carried out high-temperature annealing processing in which we controlled the Mg vapor pressure of La 4MgNi 19 alloy using a temperature-gradient furnace. By controlling the Mg vapor pressure under the sealing atmosphere, we successfully obtained homogeneous La 4MgNi 19. We prepared a P Mg-T diagram of the phases formed for La 4MgNi 19 composition, and found the optimum annealing conditions for the La 4MgNi 19 phase. The optimum annealing conditions obtained were between T= 1123 K, P Mg = 0.4 kPa and T = 1223 K, P Mg = 2 kPa. However, we found the coexistence of 3R-type and 2H-type structures, which are polytypes of La 4MgNi 19. The lattice constants of the 3R type were a = 0.5031 nm, c = 4.826 nm, and those of the 2H type were a = 0.5032 nm, c = 3.216 nm. The hydrogen storage characteristics of the annealed alloy were obtained by measuring the PCT curves at 333 K. The PCT curves showed an almost flat plateau, P H2 = 0.1 MPa, H/M= 1.1, 1.5 mass%H 2, and good cycle characteristics. It was confirmed that the dehydrogenated alloy retained the same structure but an expansion of 1 to 2% was observed in the c-axis.
AB - In La-Mg-Ni system hydrogen storage alloys, which have been attracting attention as a promising negative electrode material for Ni-MH secondary batteries, there are many phases with a variously layered stacking structure. When subjected to annealing at high temperature, the composition of these alloys becomes inhomogeneous due to the volatilization of Mg. It is therefore difficult to prepare a single phase by the normal annealing procedure. We carried out high-temperature annealing processing in which we controlled the Mg vapor pressure of La 4MgNi 19 alloy using a temperature-gradient furnace. By controlling the Mg vapor pressure under the sealing atmosphere, we successfully obtained homogeneous La 4MgNi 19. We prepared a P Mg-T diagram of the phases formed for La 4MgNi 19 composition, and found the optimum annealing conditions for the La 4MgNi 19 phase. The optimum annealing conditions obtained were between T= 1123 K, P Mg = 0.4 kPa and T = 1223 K, P Mg = 2 kPa. However, we found the coexistence of 3R-type and 2H-type structures, which are polytypes of La 4MgNi 19. The lattice constants of the 3R type were a = 0.5031 nm, c = 4.826 nm, and those of the 2H type were a = 0.5032 nm, c = 3.216 nm. The hydrogen storage characteristics of the annealed alloy were obtained by measuring the PCT curves at 333 K. The PCT curves showed an almost flat plateau, P H2 = 0.1 MPa, H/M= 1.1, 1.5 mass%H 2, and good cycle characteristics. It was confirmed that the dehydrogenated alloy retained the same structure but an expansion of 1 to 2% was observed in the c-axis.
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U2 - 10.2320/jinstmet.70.158
DO - 10.2320/jinstmet.70.158
M3 - Article
VL - 70
SP - 158
EP - 161
JO - Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals
JF - Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals
SN - 0021-4876
IS - 2
ER -