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

12 Citations (Scopus)

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

All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics
  • Mechanics of Materials
  • Metals and Alloys
  • Materials Chemistry

Fingerprint Dive into the research topics of 'Annealing conditions with Mg vapor-pressure control and hydrogen storage characteristic of la <sub>4</sub>MgNi <sub>19</sub> hydrogen storage alloy'. Together they form a unique fingerprint.

  • Cite this