Alloys- hydrogen accumulators: experimental investigations :: SPE RESST

Alloys-hydrogen accumulators: experimental studies

Among the problems, the successful solving of which will permit to realize a wide introduction of hydrogen power engineering, the key one is the problem of efficient and inexpensive hydrogen storage. One of advanced technologies of hydrogen accumulation and storage is the metal-hydride technology including the hydrogen accumulation in the alloys-accumulators with subsequent hydrogen release as a result of alloy heating.

For hydrogen accumulation the most promising are the alloys of Zr-V type, in particular, ZrV₂alloys. Hydrides of these alloys are applied as a source of pure and active hydrogen in different plasma processes. As a rule, in this case one uses the compound ZrV₂, obtained by the arc-melting method, having a rather coarse-grained structure.

The goal of the fulfilled experimental studies was to study the influence of structure and composition on the properties of Zr-V alloys as hydrogen absorbers. The presented work is carried out jointly with the Institute of Solid State Physics and Materials Science of NSC KIPT.

For investigations selected were four compositions: stoichiometric ZrV₂ alloy, alloys being on the left and on the right from the stoichiometry (Zr_0.29V_0.71 и Zr_0.38V_0.62), and eutectic Zr_0.6V_0.4alloy. Every of alloys were investigated in both the fast-quenching form and the cast form.

The investigation of the hydrogen capacitance of alloys under pressure to 3.5 atm was carried out by the volumetric method: in the closed volume an alloy specimen was exposed to the contact with hydrogen.

The facility (see Figure 1) comprises a working chamber with a test specimen, a pumping system, a pressure measuring system, a system of evacuation and specimen regeneration. The working chamber is a stainless-steel container with the specimen of 10 mm diameter and 140 mm length connected to other facility systems via the ripple joint. For changing the test specimen the container bottom is cut, the specimen is changed and the container is welded by the argon-arc welding.

Figure 1 – Layout view of the installation for investigation of the processes of hydrogen release from the hydrogen-saturated alloys in the course of vacuum heating.

Figure 2 presents the characteristic results obtained by the mass-spectrometric investigations of the processes of hydrogen release from the hydrogen-saturated alloys in the course of vacuum heating.

Figure 2 – Temperature curves of hydrogen release from the hydrogen-saturated Zr-V alloys in the fast-quenched state.

The main results of these investigations are given below.

In Table 1 given are the maximum amounts of hydrogen desorbed at temperatures to

Table 1 - Maximum amounts of hydrogen desorbed at temperatures to 900°С obtained from the results of mass-spectrometric investigations.

Composition	Wt % H
Zr_0,6V_0,4 эвт + H₂	2,38
ZrV₂ + H₂	2,308
Zr_0,37V_0,62 + H₂	2,86
Zr_0,28V_0,71 + H₂	2,97
Zr_0,6V_0,4 эвт FQ + H₂	1,758
Zr – V₂ FQ + H₂	1,16
Zr_0,37V_0,62 FQ + H₂	2,4
Zr_0,28V_0,71 FQ + H₂	2,776

FQ - Fast Quenched

The temperature of hydrogen absorption activation is essentially dependent on the composition and structural state of alloys. A minimum activation temperature (100°С) was observed for Zr_0.29V_0.71 alloy being in the fast-quenched state;

In the case of Zr-V alloy saturation in the temperature range to 400°С, independently on the composition and the state, the main part of hydrogen is absorbed to pressure of 0.05 MPa;

The structural state exerts essential influence on the alloy-hydrogen interaction. Analysis of the hydrogen amount retained by alloys shows that in all the cases cast alloys absorb a greater amount of hydrogen (up to 2.7wt %);

The processes of hydrogen release are depending also on the composition and state of alloys. A complex character of these processes represents a multiphase character of the alloys under consideration.