Annealing conditions with Mg vapor-pressure control and hydrogen storage characteristic of la 4MgNi 19 hydrogen storage alloy

Hiroshi Hayakawa, Hirotoshi Enoki, Etsuo Akiba

Research output: Contribution to journalArticle

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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 languageEnglish
Pages (from-to)158-161
Number of pages4
JournalNippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals
Volume70
Issue number2
DOIs
Publication statusPublished - Feb 1 2006

Fingerprint

Hydrogen storage alloys
Pressure control
Hydrogen storage
Vapor pressure
vapor pressure
Annealing
annealing
hydrogen
storage batteries
vaporizing
Secondary batteries
sealing
curves
electrode materials
Chemical analysis
Vaporization
Thermal gradients
Lattice constants
furnaces
plateaus

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 journalArticle

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