Dependence of hydrogen sorption-desorption on the structure of amorphous and amorphous-crystalline Fe62

Dependence of hydrogen sorption-desorption on the structure of amorphous and amorphous-crystalline Fe_62.7Nd_33.7B_1.1Cu_1.5Ti_1.0 alloys

Chem. Met. Alloys 11 (2018) 85-91

https://doi.org/10.30970/cma11.0372

Gregory BREKHARYA, Tetyana PRYADKO, Volodymyr DEKHTYARENKO, Vasyl LYAKISHEV, Nataliya LYASHENKO, Vira BOVDA

Thin films of Fe_62.7Nd_33.7B_1.1Cu_1.5Ti_1.0 alloy, promising for use as permanent magnets with high values of H_Сjand B_r, were obtained by quenching from the liquid state in pure helium atmosphere. The sorption properties and kinetics parameters of the hydrogenation and dehydrogenation processes of amorphous and amorphous-crystalline alloys were investigated by Sieverts’ method. The temperature of onset of intensive hydrogen absorption was determined by the kinetic dependence T = f(t), p = f(t). The amount of absorbed hydrogen m_H[g] and the hydrogenation rate change v [g/s] in the process of hydrogen saturation were calculated from the pressure change in a closed volume. It was established that the hydrogenation process is controlled by the degree of amorphousness of the obtained thin films. The more amorphous the component, the slower the hydrogen absorption, and it occurs at higher temperatures. It was found that at ~790±5 K the amorphous component decomposes into an equilibrium of Nd, Fe₁₄Nd₂B, and Fe₄Nd_1,1B₄ phases in both types of film and precipitated Nd takes part in the hydrogenation process at this temperature. The coexistence of two metal hydride phases possessing different properties is possible in partially hydrogenated films and their volume ratio can be regulated by appropriate selection of the sorption-desorption process parameters. The hydrogen brittleness of the samples may be used to obtain microstructured films with a grain size of 50-300 nm.

X-ray diffraction patterns of hydrogenated (а, c) and dehydrogenated (b, d) Fe_62.7Nd_33.7B_1.1Cu_1.5Ti_1.0 alloy films (а, b – 1^st cycle, c, d – 2^nd cycle).

Keywords

Permanent magnets / Amorphous-crystalline state / Hydrogenation-dehydrogenation process / Disproportionation / Hydride phases