Mechanically activated metathesis reaction in NaNH2–MgH2 powder mixtures

Abstract

The present work addresses the kinetics of chemical transformations activated by the mechanical processing of powder by ball milling. In particular, attention focuses on the reaction between NaNH 2 and MgH 2 , specific case studies suitably chosen to throw light on the kinetic features emerging in connection with the exchange of anionic ligands induced by mechanical activation. Experimental findings indicate that the mechanical treatment of NaNH 2 -MgH 2 powder mixtures induces a simple metathetic reaction with formation of NaH and Mg(NH 2 ) 2 phases. Chemical conversion data obtained by X-ray diffraction analysis have been interpreted using a kinetic model incorporating the statistical character of the mechanical processing by ball milling. The apparent rate constant measuring the reaction rate is related to the volume of powder effectively processed during individual collisions, and tentatively connected with the transfer of mechanical energy across the network formed by the points of contact between the powder particles trapped during collisions.

Efficient Synthesis of Alkali Borohydrides from Mechanochemical Reduction of Borates Using Magnesium–Aluminum-Based Waste

“…where α represents the mass fraction of LiBH 4 formed during the mechanochemical reaction and k is the apparent rate constant. The best-fitted line (dark full line) allows an estimate of the k value for the LiBH 4 formation process, which is equal to 5.68 10 −3 min −1 , one order of magnitude higher, for example, than the one estimated in the mechanically-induced metathesis reaction of Mg(NH 2 ) 2 (8.39 10 −4 min −1 ) [66]. In contrast, NaBH 4 was not identified for the sample after 5 h of ball milling.…”

Preface to the special section on mechanochemical synthesis

“…There are three articles [6][7][8] dealing with different materials for hydrogen production and storage. Garroni et al [6] and Hlova et al [7] focused on the use of mechanical milling to induce a metathesis or displacement reaction and produce metal hydrides. Garroni et al [6] showed a fine example of the differences in the reaction pathways of a specific system, when it is either thermally or mechanically activated.…”

“…Garroni et al [6] and Hlova et al [7] focused on the use of mechanical milling to induce a metathesis or displacement reaction and produce metal hydrides. Garroni et al [6] showed a fine example of the differences in the reaction pathways of a specific system, when it is either thermally or mechanically activated. Hlova et al described [7] a novel, quantitative, and solvent-free mechanochemical method to produce alane at room temperature, from a mixture of NaH and AlCl 3 .…”

Recent Progress and New Perspectives on Metal Amide and Imide Systems for Solid-State Hydrogen Storage

“…Effect of high-energy ball milling on the NaNH 2 /MgH 2 systems with different stoichiometry, 2:1 and 2:3, have also been evaluated [155][156][157]. The mechanically activated metathesis reaction occurred for the 2:1 system, ball milled for a prolonged milling time.…”