Search

A hydride-forming element titanium (Ti) was selected as an additive to improve the hydrogen uptake and release properties of MgH2. The hydrogen uptake and release properties of three Ti-added MgH2 alloys [named MgH2-xTi (x = 6, 12, and 15)] prepared by milling in hydrogen (reactive mechanical grinding) were investigated and those of MgH2-12Ti were studied in more detail because it had the highest initial hydrogen uptake and release rates and the largest quantities of hydrogen absorbed and released for 60 min. At the cycle number, n, of one (n = 1), MgH2-12Ti absorbed 4.01 wt.% H for 2.5 min and 6.39 wt.% H for 60 min at 573 K in 12 bar H2, having an effective hydrogen storage capacity of 6.39 wt.%. MgH2-12Ti released 0.44 wt.% H for 2.5 min and 1.86 wt.% H for 60 min at 593 K in 1.0 bar H2. γ-MgH2, TiH1.924, and MgO were formed during reactive mechanical grinding. We believe that the brute forces and tensile, compressive, or shear stresses, which are applied to the materials during reactive mechanical grinding, introduce imperfections, fabricate cracks, expose fresh and clean surfaces, decrease the particle size, and disperse the additive among the particles. The γ-MgH2, TiH¹.924, and MgO formed during reactive mechanical grinding and their pulverization during reactive mechanical grinding are believed to make these effects stronger. [ABSTRACT FROM AUTHOR]

Magnesium has excellent hydrogen-storage properties except low hydriding and dehydriding rates. In the present work, titanium (Ti) was chosen as an additive to increase the hydriding rate of Mg and the dehydriding rate of MgH2. 15 wt.% Ti was added to MgH2 by milling in hydrogen (reactive mechanical grinding). The hydriding and dehydriding features of the Ti-added MgH2 composite (named 85 MgH2 + 15 Ti) were investigated. At the first cycle (n = 1), 85 MgH2 + 15 Ti absorbed 2.96 wt.% H for 2.5 min and 5.51 wt.% H for 60 min at 593 K in 12 bar H2, having an effective hydrogenstorage capacity of 5.51 wt.%. β-MgH2, γ-MgH2, TiH1.924, MgO, and MgTi2O4 were formed during reactive mechanical grinding. Reactive mechanical grinding of MgH2 with Ti is believed to create imperfections, produce cracks and clean surfaces, and decrease particle sizes. The phases formed during reactive mechanical grinding and their pulverization during reactive mechanical grinding are believed to make these effects stronger. [ABSTRACT FROM AUTHOR]

The addition of CMC (Carboxymethylcellulose, Sodium Salt) may improve the hydrogen uptake-release properties of Mg since it has a relatively low melting point and the melting of CMC during transformation-involving milling may make the milled samples be in the good states to absorb and release hydrogen rapidly. Samples with compositions of 95 w/o Mg + 5 w/o CMC (named Mg-5CMC) were made through transformation-involving milling. Mg-5CMC was activated in about 3 hydrogen uptake-release cycles. After activation, Mg-5CMC had a higher beginning hydrogen uptake rate and a larger amount of hydrogen absorbed in 60 min, U (60 min), than milled Mg. At the third cycle (CN = 3), Mg-5CMC had a very high beginning hydrogen uptake rate (1.45 w/o H/min) and a very large U (60 min) (7.18 w/o H), showing that the activated Mg-5CMC has an effective hydrogen-storage capacity of about 7.2 w/o at 593 K in hydrogen of 12 bar at CN = 3. Mg-5CMC after transformation-involving milling contained Mg and very small amounts of ß-MgH2 and MgO, with no evidence of the phases related to CMC. The milling in hydrogen of Mg with CMC is believed to fabricate defects and cracks and lessen the particle size. To the best of our knowledge, this study is the first one in which a polymer CMC is added to Mg by transformation-involving milling to improve the hydrogen uptake-release properties of Mg. [ABSTRACT FROM AUTHOR]