RESUMEN
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.
RESUMEN
We report the dramatic effect of applied pressure and magnetic field on the layered intermetallic compound Pr(0.5)Y(0.5)Mn(2)Ge(2). In the absence of pressure or magnetic field this compound displays interplanar ferromagnetism at room temperature and undergoes an isostructural first order magnetic transition (FOMT) to an antiferromagnetic state below 158 K, followed by another FOMT at 50 K due to the reemergence of ferromagnetism as praseodymium orders (T(C)(Pr)). The application of a magnetic field drives these two transitions towards each other, whereas the application of pressure drives them apart. Pressure also produces a giant magnetocaloric effect such that a threefold increase of the entropy change associated with the lower FOMT (at T(C)(Pr)) is seen under a pressure of 7.5 kbar. First principles calculations, using density functional theory, show that this remarkable magnetic behavior derives from the strong magnetoelastic coupling of the manganese layers in this compound.
RESUMEN
Structural, magnetic and magnetocaloric properties of the Mn(0.94)Ti(0.06)CoGe alloy have been investigated using x-ray diffraction, DC magnetization and neutron diffraction measurements. Two phase transitions have been detected, at T(str) = 235 K and T(C) = 270 K. A giant magnetocaloric effect has been obtained at around T(str) associated with a structural phase transition from the low temperature orthorhombic TiNiSi-type structure to the high temperature hexagonal Ni(2)In-type structure, which is confirmed by neutron study. In the vicinity of the structural transition, at T(str), the magnetic entropy change, -ΔS(M) reached a maximum value of 14.8 J kg(-1) K(-1) under a magnetic field of 5 T, which is much higher than that previously reported for the parent compound MnCoGe. To investigate the nature of the magnetic phase transition around T(C) = 270 K from the ferromagnetic to the paramagnetic state, we performed a detailed critical exponent study. The critical components γ, ß and δ determined using the Kouvel-Fisher method, the modified Arrott plot and the critical isotherm analysis agree well. The values deduced for the critical exponents are close to the theoretical prediction from the mean-field model, indicating that the magnetic interactions are long range. On the basis of these critical exponents, the magnetization, field and temperature data around T(C) collapse onto two curves obeying the single scaling equation M(H,ε) = ε(ß)f ± (H/ε(ß+γ)).
RESUMEN
In Malaysia, most colored wastewater from dyeing factories is discharged to the environment causing serious problems. In this paper the influence of several reacting conditions, i.e. H2O2, pH, Ultraviolet (UV) intensity and dye concentration, on the performance of the immobilized system is discussed. The pH of the solution was varied from 3 to 11 while H2O2 concentration tested was from 10(-4) M to 5 x 10(-2) M. UV was tested at 365 nm and 254 nm, while dye concentration ranged from 2.5 x 10(-4) M to 10(-3) M. The influence of the reacting conditions was assessed based on absorbance. Using an OG concentration of 10(-3) M, the degradation increases from 17.8% to 49.7%. Optimum concentration of H2O2 was found to be 5 x 10(-3) M for degradation. Increasing the intensity of the UV light via shorter light wavelength also improves the performance of the system. Increasing the concentration of the dye reduces the overall performance of the system. Using the dye concentration of 2.5 x 10(-4) M (H2O2 = 10(-2) M, lambda = 254 nm, pH = 11), gives a degradation of 93.2%. At dye concentration of 10(-3) M, the performance was reduced to 53.1%.