ELECTROCHEMICAL PROPERTIES OF AB(5)-TYPE HYDRIDE-FORMING COMPOUNDS PREPARED BY MECHANICAL ALLOYING

Two types of intermetallic compounds, LaNi4M with M=Mn, Co, Cu and Al and polysubstituted alloys Mm(NiAlMnCo)(5) with Mm=Mischmetal were syn thesized by mechanical alloying. In most cases, 10 h grinding was suff icient to obtain single phase alloys with crystallites of about 6 nm a nd particles ranging between 5 and 80 mm in diameter. The polysubstitu ted MmNi(3.6)Al(0.35)Mn(0.25)Co(0.8) alloys, once removed from the gri nding container, were found to present an electrochemical capacity of 159 mA h/g. Such a capacity was increased to 216.3, 241.7 and 273.5 mA h/g by a post-anneal step under vacuum to temperatures of 673, 873 an d 1073 K, respectively. The various electrochemical capacity depends o n both surface states and internal strains in the sample so that the h eat treatments release these strains and enhance the capacity.