Notable hydriding properties of a nanostructured composite material of the Mg2Ni-H system synthesized by reactive mechanical grinding

Protium Absorption/Desorption Characteristics of Mg<SUB>2</SUB>Ni/LaNi<SUB>5</SUB> Composite

“…7,8) This phenomenon occurs when the phase capable of protium absorption/desorption at low temperatures undergoes expansion/contraction during the reaction with protium and this expansion/contraction applies strain to the other neighbouring phase that can only absorb/desorb protium at high temperatures, thereby facilitating the reaction of the latter at low temperatures. The same result was also obtained by Zaluska et al 9) Furthermore, Orimo et al 2) reported that synergy effect occurred in ball-milled Mg-Ni alloys during hydrogen desorbing process for the nano-amorphous region. Similarly, Nagai et al 10) reported that in Mg-x mass%LaNi 5 (x = 10-60) sintered composite, LaNi 5 addition significantly lowered the temperature at which the hydrogen absorption of magnesium was initiated during the initial hydrogenation process, and the subsequent hydriding rate was also accelerated by the addition of up to 30% LaNi 5 , beyond which the hydriding rate decreased steeply.…”

“…The LaNi 5 phase of the composite is expected to absorb protium of 0.7 mass%, which is half of the theoretical absorption content of LaNi 5 single phase. Similarly, the protium content of the Mg 2 Ni phase of that composite should be 1.8 mass%, which is half of the theoretical absorption content of Mg 2 Ni single phase. Therefore, the maximum theoretical absorption content of Mg 2 Ni-50 mass%LaNi 5 composite is 2.5 mass%.…”

“…This phenomenon is the so-called 'cooperative phenomenon that hydrogen exhibits in nano-composite systems by elastic interactions'. 2,16) Other specimens start desorbing protium like as-cast Mg 2 Ni alloy. 14) Since protium absorption at 250…”

“…However, it has problems of high protium absorption/desorption temperature and slow reaction kinetics. Therefore, numerous studies are being carried out on the use of nanocryastalline and amorphous phases obtained by mechanical alloying [2][3][4] for the purpose of lowering the protium absorption and desorption temperature. Furthermore, development of new protium absorbing Magnesium system alloys is also being vigorously pursued.…”

Hydrogenation properties of mechanically milled Mg2Ni0.8Cr0.2-CoO/Al2O3 composites

“…However, as Mg-based alloys desorb hydrogen at temperatures higher than 600 K, they are not applicable to practical use. Many researches have studied to improve hydriding/dehydriding kinetics and to lower the working temperature (Wang et al, 2002;Tsushio et al, 1998;Spassov and Köster, 1998;Orimo et al, 1997). Among various methods, ranging from element substitution, addition of a catalytic component, and surface treatment to the introduction of non-conventional fabrication methods, composite formation has been generally accepted as a simple and effective method.…”