Vasiljev A. Kinetic of hydrogen-induced phase trans-formation in intermetallic compounds RFe2 (R=Tb,Dy).

The work is devoted to studying kinetics of the hydrogen induced phase decomposition (HIPD) of an intermetallic compound RFe2 (R=Tb, Dy) onto RH2 and Fe. Highly sensitive measuring technique was developed enabling permanent control the decomposition degree using the ferromagnetic phase re-sponse. Experimental data validated using X-ray diffraction analysis. HIPD kinetics was studied in the hydrogen pressure range from 1.6 to 16.2 kPa and temperature range from 450°С to 600°С. It was established that: -Intermetallic compounds RFe2 reveal two-stage HIPD kinetics. The first stage is characterized by a constant decomposition rate. The second stage is characterized by the steadily decreasing de-composition rate. -HIPD is thermally activated process with the activation energy within 48 to 60 kJ/mol. The process rate grows with hydrogen concentration (pressure) increase as well as specific phase inter-face area increase. -HIPD kinetics for hybrid intermetallic compounds TbnDymFe2(m+n) is determined by the metal with lowest affinity to hydrogen. -HIPD mechanism consists in direct nucleation and growth of RH2 and Fe phase domains due to contraction of RFe2 domains without any intermediate or amorphous phases.