چكيده به لاتين
In this study the hydrogen storage properties of the nanocrystalline Mg-Ti-Cr-Fe composite powders were evaluated. Two kind of nanocrystalline composite with the same Compound of Mg-60 at. % (28Ti-32Cr-40Fe) was synthesized via mechanical milling under argon atmosphere. In the first composite, called sample A, all Metal elements of Mg, Cr, Fe & Ti was milled up to 60 hour together. In the second composite, called sample B, at the first 30 hour of ball milling, three elements of Mg, Cr & Fe Were present. After 30 hours, Ti Elemental Powder was addet to vial and the milling operation was continued up to 60 hours. The hydrogen absorption/desorption properties of these two composite powders were investigated. The phases formed after 60 hours milling in sample A were consist of: FeTi, Cr2Ti, Cr0.26Fe1.74 & Ti5Cr7Fe17 and in sample B were: FeCr, Cr2Ti & Fe2Ti. the phases which were formed after hydrogenation, in Sample A were: Cr0.26Fe1.74, Cr1.8TiH5.3, FeTiH, FeTiH2, Ti5Cr7Fe17H0.07, β-MgH2 & γ-MgH2 and in sample B were: FeCr, Cr1.8TiH5.3, Fe2Ti & β-MgH2. the crystallite size of magnesium matrix was reduced up to 6 nm in sample A and 18 nm in Sample B. Significant differences in the particle morphology were observed in sample A than sample B. in sample A more particle refinement and homogenous dispersion of particles, in the shape and size, was achieved. Therefore the composites containing Ti from the beginning of milling operation was led to the formation of compounds with enhanced catalytic effect, more homogeneous morphology, smaller particle size and more fine grained nanostructure. In the temperature of 400 °C, sample A absorb 3.4 wt. % H2 at the equilibrium pressure of 0.27 MPa and desorb 3.3 wt. % H2 at the equilibrium pressure of 0.12 MPa. At the same temperature, sample B absorb 2.9 wt. % H2 at the equilibrium pressure of 0.42 MPa and desorb 2.7 wt. % H2 at the equilibrium pressure of 0.21 MPa. It is obviously seen that sample A has higher hydrogen storage capacity and enhanced hydrogen absorption/desorption properties. As a result, these improved features of sample A could be attributed to the presence of Ti from the Beginning of mechanical milling process.
