Studies on improvement of hydrogen storage capacity of AB 5 type:MmNi 4.6Fe 0.4 alloy (original) (raw)

In this work, the mechanical milling of a FeTiMn alloy for hydrogen storage purposes was performed in an industrial milling device. The TiFe hydride is interesting from the technological standpoint because of the abundance and the low cost of its constituent elements Ti and Fe, as well as its high volumetric hydrogen capacity. However, TiFe is difficult to activate, usually requiring a thermal treatment above 400 ºC. A TiFeMn alloy milled for just 10 min in a 100 L industrial milling device showed excellent hydrogen storage properties without any thermal treatment. The as-milled TiFeMn alloy did not need any activation procedure and showed fast kinetic behavior and good cycling stability. Microstructural and morphological characterization of the as-received and as-milled TiFeMn alloys revealed that the material presents reduced particle and crystallite sizes, even after such short time of milling. The refined microstructure of the as-milled TiFeMn is deemed to account for the improved hydrogen absorption-desorption properties.

The hydrogenation characterizations of the hydrogen storage alloy MmNi4.22Co0.48Mn0.15Al0.15 (Mm= mischmetal), and the effect of hydrogenation/dehydrogenation (H/D) cycling on its structural and morphological properties are investigated. The results indicate that after several H/D cycles the alloy was pulverized into fine particles, but it kept its hexagonal CaCu5-type structure. The pressure-composition (PC) isotherms for hydrogen absorption/desorption and absorption kinetic were measured in temperature range of 293-338 K. The absorption plateau pressures were determined to be ~ 0.51, 1.22 and 2.49 bar at 293, 313 and 33 K respectively, with a maximum hydrogen storage capacity of about 5.78 at 293 K. The enthalpy (H), entropy (S) and the activation energy of reactions (Ea) were also calculated. The results show that the hydrogenation reaction rate increases with an increase in the operating temperature or pressure. The Jander diffusion (JDM) and Johnson-Mehl-Avrami (JMA) models were employed and the kinetic of hydrogenation was analyzed in detail for hydriding reaction (rate controlling steps) mechanism. The obtained results indicate that the MmNi4.22Co0.48Mn0.15Al0.15 alloy has potential to be suitable for use in practical applications.

The effects of different synthesis procedures on the microstructure and hydrogen uptake characteristics of the Mg15Fe materials were studied. The applied processes of synthesis consisted basically on ball milling in argon atmosphere followed by a hydriding reaction. Two mill devices with distinct milling modes were employed, i.e. a low energy mill (LEM) (Magneto Uni-Ball-Mill II) and a high energy mill (HEM) (Fritsch Planetary Mill, P6). The HEM sample showed better Mg–Fe mixing degree than the sample obtained from the LEM process due to the small particles of Fe resulting from the larger amount of mechanical energy transferred to the materials by the HEM device. The better Mg–Fe contacting was responsible for the higher hydrogen capacity and faster hydrogen uptake rate of the high energy milled material. Therefore, the HEM procedure was more effective than the LEM. The hydrogen uptake properties of the HEM synthesized material were compared with other Mg-based materials obtained via inert and reactive ball milling without a subsequent activation step. This study showed that Mg15Fe mixture of powders synthesized via reactive ball milling in hydrogen (RBM–LEM) has higher hydrogen capacity (5.5 wt% H) and faster kinetics than samples with the same composition milled in argon (LEM – 1.65 wt% H and HEM 1.87 wt% H). Nevertheless, a superior hydrogen capacity (6.5 wt% H) were obtained by adding LiBH4 to Mg15Fe via HEM in argon atmosphere.

ABSTRACT Mg76Ti12Fe12-xNix(x=0,4,8,12) alloys were prepared by mechanical alloying and the hydrogen storage properties were investigated systematically. In Mg76Ti12Fe12 and Mg76Ti12Ni12Ti12 alloys, the main binary alloy phase is Fe2Ti and Mg2Ni, respectively. There are same binary alloy phase structures included Fe2Ti, Mg2Ni and NiTi in Mg76Ti12Fe8Ni4 and Mg76Ti12Fe4Ni8 alloys. For Mg76Ti12Fe12-xNix(x=0,4,8,12) alloys, the hydrogen storage capacity is 2.88, 3.31, 3.12 and 2.24 wt%, respectively. The hysteresis between hydrogen absorption and desorption decreases gradually with increasing the amount of substitution Ni for Fe. Mg76Ti12Fe8Ni4 shows the highest hydrogen absorption and desorption rate among Mg76Ti12Fe12-xNix(x=0,4,8,12) alloys. Fe and Ni coexistence is favorable to improve hydrogen storage properties. For Mg76Ti12Fe8Ni4 alloy, the amorphous degree increase with the milling time, and the amorphous degree increase is unfavorable to improve hydrogen storage capacity.

Abstrak Hidrogen memiliki nilai kalor tertinggi dari semua unsur kimia, regeneratif dan ramah lingkungan. Untuk aplikasi secara mobile dan stasioner kepadatan volumetrik dan gravimetrik hidrogen dalam bahan penyimpanan menjadi sangat penting. Paduan Fe-Ti sebagai penyimpan hidrogen telah diterapkan di berbagai bidang karena mampu menyerap hidrogen pada suhu kamar. Sayangnya, kapasitas menyimpan hidrogen sangat rendah. Sintesis dan karakterisasi paduan Ti-Fe-Al dengan perbandingan atom Fe: Ti: Al = 10: 10: 1 dibuat dengan teknik pemaduan mekanik dalam larutan toluena dan sifat penyerapan hidrogen dari sintetik yang dihasilkan telah dilakukan. Serbuk Fe-Ti-Al digiling bersama-sama dengan waktu milling 30 jam di dalam mesin ball mill energi tinggi. Spesimen yang digiling dianalisis dengan difraktometer sinar-X. Analisis kualitatif dan kuantitatif dihitung dengan metode Rietveld yang dikembangkan oleh Fuji Izumi. Analisis pola difraksi sinar-x hasil giling paduan Fe-Ti-Al menunjukkan ha...