Hydrogen-occluding alloy and method for production thereof

Abstract

A hydrogen storage alloy and its production method are disclosed, which has an extremely high effective hydrogen storage capacity in the pressure range from 0.001 to 10 MPa, and a variety of use. The alloy is principally of a body-centered cubic crystal structure, and represented by the compositional formula Cr a Ti b V c Fe d M e X f (M: Al etc.; X: La etc.; 30≦a≦70, 20≦b≦50, 5≦c≦20, 0≦d≦10, 0≦e≦10, and 0≦f≦10, a+b+c+d+e+f=100). The alloy contains 0.005 to 0.150 wt % of O 2 , and has hydrogen absorption-desorption capability of not less than 2.2% of its weight from 0 to 100° C. and from 0.001 to 10 MPa. The method includes step (a) of melting starting materials for the alloy, deoxidizing step (b) such as step (b1) of blowing Ar into the alloy melt, and casting step (c).

What is claimed is:  
     
         1 . A hydrogen storage alloy principally of a body-centered cubic crystal structure, and represented by the compositional formula Cr a Ti b V c Fe d M e X f , wherein M stands for one or more elements selected from the group consisting of Al, Mo, and W; X stands for one or more elements selected from the group consisting of La, Mm (misch metal), Ca, and Mg; a, b, c, d, e, and f each denotes a value in atomic percent, and 30≦a≦70, 20≦b≦50, 5≦c≦20, 0<d≦10, 0≦e≦10, and 0≦f≦10, provided that a+b+c+d+e+f=100, 
 wherein said alloy comprises 0.005 to 0.150 wt % of O 2 , and has hydrogen absorption-desorption capability of not less than 2.2% of its weight in a temperature range from 0 to 100° C. and in a pressure range from 0.001 to 10 MPa.  
 
     
     
         2 . The hydrogen storage alloy of  claim 1 , wherein e in the compositional formula satisfies 0<e≦10.  
     
     
         3 . The hydrogen storage alloy of  claim 1 , wherein f in the compositional formula satisfies 0<f≦10.  
     
     
         4 . The hydrogen storage alloy of  claim 1 , wherein e in the compositional formula satisfies 0<e≦10, and f satisfies 0<f≦10.  
     
     
         5 . A method for producing a hydrogen storage alloy of  claim 1 , comprising: 
 melting step (a) of melting starting materials for a hydrogen storage alloy of  claim 1  to prepare an alloy melt;    at least one deoxidizing step (b) selected from the group consisting of deoxidizing step (b1) of blowing argon gas into the alloy melt, deoxidizing step (b2) of retaining the alloy melt in vacuum of not higher than 0.1 Pa, and deoxidizing step (b3) of adding and retaining in the alloy melt one or more elements selected from the group consisting of La, Mm, Ca, and Mg; and    casting step (c) of solidifying the alloy melt.    
     
     
         6 . The method of  claim 5  further comprising, after step (c), step (d) of retaining a solidified alloy in a temperature range from 1150 to 1450° C. for 1 to 180 minutes, followed by cooling to 400° C. or lower at a cooling rate of not lower than 100° C./sec.  
     
     
         7 . The method of  claim 5 , wherein a melting temperature in said melting step (a) is not higher than 1700° C.  
     
     
         8 . The method of  claim 5 , wherein said starting materials in said melting step (a) comprise at least one of a Fe—V alloy, a Cr—Ti alloy, a Cr—V alloy, or V metal containing Al prepared by the thermit process.