Mechanochemically driven nonequilibrium processes in MNH2–CaH2 systems (M=Li or Na)

Mechanochemical transformations in NaNH2-MgH2 mixtures

“…A similar discrepancy was recently reported in 2LiNH 2 -CaH 2 system, which under thermochemical conditions decomposes to Li 2 Ca(NH) 2 and can be hydrogenated to Ca(NH 2 ) 2 and LiH, in analogy to (R2) [18]. However, neither Li 2 Ca(NH) 2 nor Ca(NH 2 ) 2 is formed during mechanical milling of 2LiNH 2 -CaH 2 mixture [19].…”

“…During the thermal decomposition of 2NaNH 2 + 3MgH 2 mixture, Mg(NH 2 ) 2 and NaMgH 3 are observed as intermediates, whereas only MgNH is detected as the intermediate product during mechanochemical reaction. These observations indicate that, in contrast to thermochemical transformations, which proceed in accordance with thermodynamic equilibrium, the reactions induced by mechanical energy may drive the reaction through nonequilibrium configurations leading to formation of different intermediate species [19].…”

Hydrogen release and structural transformations in LiNH2–MgH2 systems

“…3b) of Li:Mg 600 sample confirms a single desorption event at about 285 • C under 3 atm He, where the diffraction peaks of both Li 2 NH and unknown (X) phase decrease, together with the appearance of ␤-Li 2 Mg(NH) 2 phase and the increase of the Mg 3 N 2 phase. Even though it is known only an hexagonal MgNH phase [24] this reaction step supports the presence of a MgNH compound as the unknown (X) phase. This event may open space for the occurrence of a cubic metastable MgNH in certain conditions, with a structure similar to that of the CaNH phase.…”

“…SXRD data are reported as a function of the scattering vector Q = 4 sin(Â)/ and assessment of structural information was made using MAUD, a diffraction analysis software based on the Rietveld method with focus on materials science studies [20]. Structural information of the Li-Mg-N-H were taken from literature: ␣-and ␤-Li2Mg(NH)2 [15], Li2Mg2(NH)3 [21], LiMgN [22], LiNH2, Mg(NH2)2 [23], and MgNH [24]. …”

Two-Peak Mystery of LiNH2–NaH Dehydrogenation Is Solved? A Study of the Analogous Sodium Amide/Lithium Hydride System

“…10 In both cases, ammonia is also produced in addition to N 2 and H 2 . Except these preliminary reports, only some scattered reports on NaNH 2 −MgH 2 , 11 NaNH 2 −CaH 2 , 12 NaNH 2 −LiAlH 4 , 13 etc. are available in the literature without detailed investigation.…”