Solid State Synthesis of Non-Equilibrium Phase in Mg-Co and Mg-Fe Systems via Bulk Mechanical Alloying

Abstract

Mg-Co and Mg-Fe systems were employed as a candidate hydrogen storage alloy. Different from Mg-Ni system, there exist no line compounds of Mg 2 Co and Mg 2 Fe. Non-equilibration of these compounds is indispensable to make solid state synthesis. Bulk mechanical alloying was applied to this non-equilibration of Mg 2 Co with success. Planetary ball milling was also utilized to discuss the process efficiency of bulk mechanical alloying. In particular, the on-line monitored energy density was used to describe the homogeneous refining and solid-state reaction with increasing the number of cycles. Through SEM observation of intermediate phase change, the solid-state reaction commences when the total energy density exceeds the critical limit. SEM/EDX and XRD analyses assured that the synthesized non-equilibrium phase should be Mg 2 Co. The Goldschmidt-factor analysis was used to determine that the synthesized Mg 2 Co has mainly fcc-structure. No significant change of XRD profiles was observed even when increasing the holding temperature. This Mg 2 Co is quasi-stable, non-equilibrium phase even at the elevated temperature. In case of Mg-Fe system, the initial elemental particle mixture was homogeneously refined. Under the similar condition to the solid-state synthesis of Mg 2 Co, however, Mg 2 Fe was not synthesized even via bulk mechanical alloying. Through precise analysis, nonequilibrium phase with high iron content was recognized, so that non-equilibration via the bulk mechanical alloying might well be effective to investigate the solid state synthesis of binary compounds even in Mg-Fe system.

Enhancing superconducting properties of MgB2pellets by addition of amorphous magnetic Ni–Co–B nanoparticles

“…Phase diagrams of Mg-Ni system show that Mg 2 Ni occurs as a stable phase at concentrations of Ni less than 35% [35][36][37]. For Mg-Co system, there is only one stable compound, MgCo 2 [35][36][37][38].…”

“…Therefore XRD analysis cannot confirm that the above phases formed, most likely because these phases were in the form of nanoparticles with poor crystallinity. [35,39,40].…”

Solid-State Synthesis of Thermoelectric Materials in Mg–Si–Ge System

“…[9][10][11] In the present study, the bulk mechanical alloying (BMA) is applied to the solid-state synthesis of ternary, semiconductive solid solution, Mg 2 Si 1Àx Ge x at the room temperature. This process was successfully used to yield various magnesium base alloys and compounds: e.g., solid-state synthesis of Mg 2 Si 12,13) and non-equilibration of Mg 2 Ni and Mg 2 Co. [14][15][16] In addition, BMA with hot pressing (HP) or hot extrusion has become a new processing to make anisotropic control of crystalline structure for improvement of thermoelectric properties in Bi-Te systems. [17][18][19][20] Although the synthesis of Mg 2 Si 1Àx Ge x was made by the melting and solidification method, 10,11) no reports were found for its solidstate synthesis at room temperature.…”

Solid-State Synthesis of Hydrogen Storage Mg<SUB>2</SUB>Co Alloys <I>via</I> Bulk Mechanical Alloying

“…The number of cyclic loading (N) was varied from N ¼ 0 to N ¼ 2500 to describe the alloying process from elemental mixture to compounds with increasing N. Details in the forging facilities and loading schedule were found elsewhere. 7,8) All through BMA, the sample material was processed in BMA at argon atmosphere and under forced cooling conditions.…”

“…It needs shorter process time, and has less or even no contamination which is an obstacle in solid-state reactions in the conventional repeated milling or attrition. 7,8) In the present study, this BMA method is applied to fabrication of Mg 2 Co alloy from the starting element constituent mixtures of magnesium and cobalt. This solidstate reaction process is first described by on-line measurement of imposed mechanical energy on BMA as well as XRD and DTA analyses.…”