Hydrogen Absorption Of Intermetallic Compounds Research Articles

In pursuit of light intermetallic hydrides

The search for a “magic” intermetallic compound, absorbing reversibly and easily copious quantities of hydrogen, has been pursued since the discovery of the first intermetallic hydrides, forty–fifty years ago. Obviously, such intermetallic compounds should contain light metal elements like Li, Mg, Al, Ca, etc. We summarize in this work the experimental evidence that sheds light on the hydrogen absorption abstinence of Al-rich intermetallic compounds. The elastic moduli and/or bonding properties of Al-containing pseudobinary compounds initially decrease and then increase as a function of the Al composition. The shear and the bulk moduli behave differently in the Al-rich portion, where they present significantly higher and lower values, respectively, than the corresponding moduli in the Al-poor region. We claim that the extensive shear stiffening inhibits the hydrogen absorption in the Al-rich compounds. An explanation for the choice of the LaSn0.22Ni0.78 compound as a sorption cryocooler in the Planck mission is suggested in view of its shear softening with respect to LaNi5. Recent attempts to find pseudobinary intermetallic hydrides, containing Li and Ca, are also presented. These attempts are conducted by considering some of the factors which regulate hydrogen absorption in intermetallic compounds.

Hydrogen-induced amorphization in CeAl alloys

Hydrogen-induced amorphization (HIA), i.e., formation of an amorphous phase by hydrogen absorption of intermetallic compounds, has been investigated in the last decade as a novel preparation method of amorphous alloys without liquid quenching. HIA is reported in many compounds, which are almost C15 Laves RM{sub 2} compounds (R = rare earth metal, M = ferromagnetic metal of Fe, Co, Ni). This leads to a question whether HIA is a popular phenomenon limited just to C15 Laves RM{sub 2} compounds. Recently, the present authors have shown that HIA occurs in many R-Al compounds (R = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er as well as Y). Furthermore, the behavior of amorphization from crystalline state and the behavior of crystallization from the corresponding amorphous state in R-Al alloys are fairly different from those in Laves RM{sub 2} compounds. For a more detail study as presented in this paper, Ce-Al alloys have been chosen because they are taken as representative. In the Ce-Al alloys, there are five intermetallic compounds. As CeAl{sub 3} and Ce{sub 3}Al{sub 11} seldom absorb hydrogen, this study will focus on Ce{sub 3}Al, CeAl and CeAl{sub 2}.

Hydrogen absorption in intermetallic compounds of thorium

The formation of ternary hydrides has been studied for 15 intermetallic compounds of thorium, (five compounds in each of the systems Th-Ni, Th-Co and Th-Fe). With the exception of the compounds richest in 3 d-metal, they all form hydrides by reaction with hydrogen gas at room temperature. The hydrides prepared include the compounds ThCoH 4, ThNi 2H 5 and Th 7Ni 3H 28- Some compounds (Th 2Co 7H 4, Th 2Fe 7H 5) have equilibrium hydrogen pressures near to 1 atmosphere at 300 K. The results are discussed in terms of a model that predicts the enthalpy of formation of a ternary hydride from the knowledge of ΔH for the corresponding binary hydrides and binary intermetallic compounds. In addition we discuss experimental results on hydrogen absorption in LaNi 5 and related compounds, published earlier. The agreement between model predictions and experiment is quite convincing.