Chemical hydrogenation of La(Fe,Si) family of intermetallic compounds

- The new method of hydrogenation of La(Fe,Si)13 compounds has been proposed.
- Method is based on the hydrogen production during reaction between La(Fe,Si)13 compounds (20-50 μm grain) and acids.
- Thermal annealing at 80 °C is needed for hydrogen homogenization in the sample after initial hydrogenation.
- ΔTad of hydrogenated LaFe11.8Si1.2 was equal to 3 K at B = 1.7T, while ΔSM = 8.5 J/kg*K at B = 2T.
- Desorption of hydrogen is a two-step process related to interface (1 step) and interstitial (2 step) hydrogen release.

In the present work, the chemical hydrogenation process of La(Fe,Si)13 compounds has been shown. It was found, that the La(Fe,Si) compound can be easily saturated with hydrogen by performing reaction with 0.6 M hydrochloric acid (HCl) for 2 h. After reaction, the heat treatment process is necessary to make hydrogenated powder homogenous. For the LaFe11.8Si1.2 micronized (<50 μm) and hydrogenated powder, the strength of the magnetocaloric effect was estimated by means of magnetocalorimetric measurements on plates consolidated with PVDF thermoplastic polymer. Magnetic entropy change was calculated by use of magnetization data acquired at magnetic fields with induction up to 2T. The adiabatic temperature change is equal to 3 K in magnetic field change 0-1.7T at 335 K, while magnetic entropy change is equal 13 J/kg*K at 2T. The structural homogeneity of initial and hydrogenated powders was validated by powder X-ray diffraction method. The amount of hydrogen in the hydrogenated compounds was evaluated using thermogravimetry method (4 H atoms per formula unit LaFe11.8Si1.2).

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