Abstract:
A material for storing hydrogen consisting of a titanium-iron alloy having 5-30 at.% of one or more metals of the group chromium, zirconium, manganese and vanadium.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a material for storing hydrogen which contains titanium and iron in a mutual ratio in gram-atoms between 4:1 and 0.67:1. The invention further relates to the hydrides formed from such materials, to a method for storing and giving off hydrogen while using such materials and their hydrides, and to an apparatus containing such materials and their hydrides for storing and giving off hydrogen. 
     It is known that mixtures of iron and titanium in the form of compounds and alloys are suitable for storing hydrogen by forming hydrides under pressure at ambient temperature. By decreasing the pressure surrounding the material and/or heating the material, hydrogen is released from the material. U.S. Pat. No. 3,516,263 and U.S. Pat. No. 3,508,414 disclose a material which contains, by weight 35-75% Ti, the remaining percent being Fe. It appears that in practice an elaborate treatment of the material is necessary, after preparation, before the material can be made to quickly absorb and release hydrogen at ambient temperature. 
     This &#34;activation treatment&#34; may, for example, consist of heating the material to a temperature of 400° C. or higher in a vacuum and while continuously evacuating, followed by cooling the material to room temperature and supplying hydrogen to a pressure of approximately 35 atmospheres, whereafter the hydrogen is again released from the material by vacuum-pumping and heating. This procedure must be repeated various times to obtain such a degree of activation that at approximately 20° C. the material can reversibly absorb and release hydrogen at a sufficient speed which depends upon the pressure surrounding the material. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to provide a material which, compared with materials which exclusively contain titanium and iron can be activated in a simple manner at room temperature. 
     It is a further object of the invention to provide an apparatus and a method for storing and giving off hydrogen while using a material which, compared with materials which exclusively contain titanium and iron, can be activated in a simple manner at room temperature. 
     In accordance with this invention these objects are satisfied by a material which contains, besides titanium and iron in the said ratios one or more materials from the group comprising by chromium, zirconium, manganese and vanadium. 
     Preferably, the composition of the material in gram-atoms is, based on the total material, 5 to 30% of one or more of the elements of the group comprising the metals chromium, zirconium, manganese and vanadium. The remainder of the material is titanium and iron in the specified mutual ratio. 
     The presence of these metals in the material results, in many cases, in the same quantity of hydrogen being absorbed at a lower hydrogen pressure as compared with materials which contain titanium and iron, only while the total capacity of absorption, in ml of hydrogen per gram of material, is in general of the same order of magnitude as with materials which contain titanium and iron only. This has the advantage that the reservoirs may be simpler in construction, as they need only be able to withstand relatively lower pressures. Furthermore, there is a greater freedom of choice so that it is possible for a given application to utilize a material having the most favorable properties as regards hydrogen absorption. For energy storage by means of hydrogen absorption, in which one wants to permit hydrogen pressures to a maximum of 2 atmospheres at approximately 20° C. in a simple apparatus, a material which contains, Ti and Fe in a mutual ratio of between 2.5:1 and 1.1:1 and Mn in a quantity of 5 to 30 atom % based on the total material has appeared particularly suitable. An example of such a material is TiFe 0 .8 Mn 0 .2. 
     The materials according to the invention are prepared by fusing the composite metals in the proper ratio by means of arc melting in a non-oxidizing, for example neutral or reducing, atmosphere or in vacuo and by cooling the casting down to room temperature. If desired the casting may now be pulverized. Activating can now be done in a simple manner at approximately 20° C. by exposing the material to hydrogen with a pressure of 30 to 40 atmospheres. Usually the material reaches its maximum capacity after only one cycle of loading with hydrogen and a subsequent release of hydrogen. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The sole FIGURE is a diagrammatic and partly cross-sectional view of an apparatus for storing hydrogen while using the materials according to the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     By fusing the relevant elements in the required quantities (namely Ti and Fe in a mutual ratio in gram-atoms of from 4:1 to 0.67:1, and one or more of Cr, Zr, Mn, and V in a quantity of 5-30 atom % of the total material) casting were produced having compositions which may be indicated by the following formulae. 
     
         ______________________________________1. TiFe.sub.0.9 Cr.sub.0.1                7. TiFe.sub.0.4 Mn.sub.0.62. TiFe.sub.0.8 Cr.sub.0.2                8. TiFe.sub.0.9 V.sub.0.13. TiFe.sub.0.7 Cr.sub.0.3                9. TiFe.sub.0.8 V.sub.0.24. TiFe.sub.0.9 Zr.sub.0.1               10. Ti.sub.0.9 FeZr.sub.0.15. TiFe.sub.0.9 Zr.sub.0.2               11. Ti.sub.0.8 Zr.sub.0.2 Fe6. TiFe.sub.0.8 Mn.sub.0.2______________________________________ 
    
     The materials indicated by the compositions 1 to 11 were activated by exposing them, at a temperature of 20° C., to hydrogen having a pressure of 30 atmospheres until hydrogen was no longer absorbed. Thereafter, hydrogen was removed from the materials while measuring the quantity of absorbed hydrogen. After this activation treatment was completed, an equilibrium was obtained in all cases within a few minutes further on exposure to a hydrogen atmosphere. The table below specifies for the above-mentioned compounds the activation time and the absorption capacity in ml of hydrogen per gram of material at 20° C. 
     
                       TABLE______________________________________                             Absorption                             capacity (2)Example  Composition Activation time (1)                             in ml/gr.______________________________________1      TiFe.sub.0.9 Cr.sub.0.1              +              2252      TiFe.sub.0.8 Cr.sub.0.2              ++             2233.     TiFe.sub.0.7 Cr.sub.0.3              +++            2294      TiFe.sub.0.9 Zr.sub.0.1              +++            2415      TiFe.sub.0.8 Zr.sub.0.2              ++++           2706      TiFe.sub.0.8 Mn.sub.0.2              ++             1907      TiFe.sub.0.4 Mn.sub.0.6              +++            2308      TiFe.sub.0.9 V.sub.0.1              ++             2429      TiFe.sub.0.8 V.sub.0.2              ++++           27310     Ti.sub.0.9 FeZr.sub.0.1              +++            24211     Ti.sub.0.8 FeZr.sub.0.2              +++            217A      TiFe        ---            230______________________________________ (1) - more than 24 hours + within 10 hours ++ within 5 hours +++ within 60 minutes ++++ within 5 minutes (2) at a hydrogen pressure of 30 atm and at 20° C. 
    
     The invention will be further explained with reference to the drawing, the only FIGURE of which shows diagrammatically and partly in cross-section an apparatus for storing hydrogen while using the materials according to the invention. In the FIGURE there is a reservoir 1 for the material 2 provided with a pressure gauge 5. A supply and discharge pipe 6 is provided with a controllable shut-off valve 4 for the hydrogen. A heating device 3 is wound around the reservoir 1. 
     Loading the material 2 with hydrogen is effectuated by pumping hydrogen, after the reservoir 1 has been evacuated, into the reservoir 1 until the pressure in the reservoir 1 rises to above the equilibrium pressure of the material 2. The hydrogen can be released from the material 2 by reducing the hydrogen pressure above the material 2 the below the equilibrium pressure or by increasing the temperature of the material 2 to above ambient temperature. 
     An advantage of the materials according to the invention is, that the equilibrium pressure at a given temperature is generally lower as compared to materials which contain only Ti and Fe, so that the reservoirs need not be designed for relatively high pressure and the reservoirs need not be exposed to high temperatures when activating the material.