Nurul Hayati Idris

Nanolayer-like-shaped MgFe2O4 synthesised via a simple hydrothermal method and its catalytic effect on the hydrogen storage properties of MgH2

In this study, the effect of nanolayer-like-shaped MgFe2O4 that is synthesised via a simple hydrothermal method on the performance of MgH2 for hydrogen storage is studied. MgH2 + 10 wt% MgFe2O4 is prepared by using the ball milling method. The MgFe2O4-doped MgH2 sample started to release H2 at approximately 250 °C, 90 °C and 170 °C lower than the milled and pure MgH2 respectively. At 320 °C, the isothermal desorption kinetic study has shown that the doped sample has desorbed approximately 4.8 wt% H2 in 10 min while the milled MgH2 desorbed less than 1.0 wt% H2. For isothermal absorption kinetics, the doped sample can absorb approximately 5.5 wt% H2 in 10 min at 200 °C. Meanwhile, the undoped sample absorbs only 4.0 wt% H2 in the same condition. The activation energy of 10 wt% MgFe2O4-doped MgH2 composite is 99.9 kJ mol−1, which shows a reduction of 33.1 kJ mol−1 compared to the milled MgH2 (133.0 kJ mol−1). X-ray diffraction spectra display the formation of new species which are Fe and MgO after dehydrogenation, and these new species are believed to act as the real catalyst that plays a crucial role in improving the sorption performance of the MgFe2O4-doped MgH2 system by providing a synergetic catalytic effect.

Systematically study on the magnetism and critical behaviour of layered NdMn1.4Cu0.6Si2

The strong dependence of the field-induced on the body-centered tetragonal ThCr2Si2-type and the critical behaviour of magnetic phase transition in NdMn2-xCuxSi2 based compounds guide us to study the substitution Mn (atomic radius = 1.35 A) by Cu (atomic radius = 1.28 A) in layered NdMn1.4Cu0.6Si2 compound. Room temperature x-ray diffraction study indicates clearly that most of the reflections can be identified with ThCr2Si2-type structure with space group I4/mmm. It found lattice parameters a slightly increases and lattice parameter c decrease compare to NdMn2Si2 as indicated the decreasing of volume structure. The Neel temperature TN is found at 340 K while Curie temperature TC found at 75 K respectively. The increasing concentration of Cu in replacement of Mn changes the magnetic phase transition from first order type for NdMn2Si2 to second order type for layered NdMn1.4Cu0.6Si2 compound as been determined by particular the S-shaped nature of the Arrott plot near TC. Our results indicate that the magnetic-field-induced magnetic phase transition plays a critical role on producing large magnetocaloric effect in these systems especially on second order type as the key for further investigation. The critical behaviour analysis in the vicinity of TC demonstrates that the magnetism of the layered NdMn1.4Cu0.6Si2 compound is governed by long range interactions.The strong dependence of the field-induced on the body-centered tetragonal ThCr2Si2-type and the critical behaviour of magnetic phase transition in NdMn2-xCuxSi2 based compounds guide us to study the substitution Mn (atomic radius = 1.35 A) by Cu (atomic radius = 1.28 A) in layered NdMn1.4Cu0.6Si2 compound. Room temperature x-ray diffraction study indicates clearly that most of the reflections can be identified with ThCr2Si2-type structure with space group I4/mmm. It found lattice parameters a slightly increases and lattice parameter c decrease compare to NdMn2Si2 as indicated the decreasing of volume structure. The Neel temperature TN is found at 340 K while Curie temperature TC found at 75 K respectively. The increasing concentration of Cu in replacement of Mn changes the magnetic phase transition from first order type for NdMn2Si2 to second order type for layered NdMn1.4Cu0.6Si2 compound as been determined by particular the S-shaped nature of the Arrott plot near TC. Our results indicate that the magne...