Partial Substitution Of Mg Research Articles

Effects of surface and bulk modifications on electrochemical and physicochemical characteristics of MgNi alloys

Effects of partial substitution of Mg in MgNi with both Ti and V and subsequent surface modification by ball-milling with graphite on electrochemical and physicochemical characteristics of amorphous MgNi alloys were investigated. It was found from thermogravimetry (TG) that hydrogen desorbability of the MgNi alloys was improved by either partial substitution with both Ti and V or surface modification with graphite, and that the combination of the partial substitution and the subsequent surface modification enhanced the hydrogen desorbability further. In charge–discharge cycle tests, the partial substitution with Ti and V or surface modification with graphite suppressed the decay of discharge capacity with increasing cycle number. Mg 0.9Ti 0.06V 0.04Ni alloy modified with graphite exhibited further improved cycle performance as compared with either unmodified Mg 0.9Ti 0.06V 0.04Ni alloy or MgNi alloy modified with graphite. These results indicate that modification of both bulk and surface of the MgNi alloys is very effective in improving hydrogen desorbability and charge–discharge cycle performance of the alloys.

Magnesium hydroxide/zinc borate/talc compositions as flame‐retardants in EVA copolymer

The fire-resistance of EVA filled with ternary systems (magnesium hydroxide/zinc borate/talc) has been investigated. The release of water from Mg(OH)2 seemed to be the predominant phenomenon which acts in relation to fire-resistance. The presence of talc as a minor component, mainly in binary compositions by partial substitution of Mg(OH)2, appeared to enhance the flame-retardant properties. It acts by forming a diffusion barrier which is able to limit the transfer of degradation products and oxygen. Synergism was also noticed between talc and zinc borate at constant Mg(OH)2 loading in ternary compositions. © 2000 Society of Chemical Industry

Magnesium hydroxide/zinc borate/talc compositions as flame-retardants in EVA copolymer

The fire-resistance of EVA filled with ternary systems (magnesium hydroxide/zinc borate/talc) has been investigated. The release of water from Mg(OH)2 seemed to be the predominant phenomenon which acts in relation to fire-resistance. The presence of talc as a minor component, mainly in binary compositions by partial substitution of Mg(OH)2, appeared to enhance the flame-retardant properties. It acts by forming a diffusion barrier which is able to limit the transfer of degradation products and oxygen. Synergism was also noticed between talc and zinc borate at constant Mg(OH)2 loading in ternary compositions. © 2000 Society of Chemical Industry

Hydrogen storage properties of nanocrystalline Mg 1.9Ti 0.1Ni made by mechanical alloying

The mechanical alloying technique was used to make nanocrystalline Mg 2Ni and Mg 1.9Ti 0.1Ni powders. Their hydrogen storage properties were characterized and compared with that of polycrystalline Mg 2Ni made by casting. It was found that the ball milled Mg 2Ni and Mg 1.9Ti 0.1Ni can absorb hydrogen at 473 K in the first cycle rapidly without prior activation. The nanocrystalline Mg 1.9Ti 0.1Ni showed the best kinetics, followed in order by mechanically alloyed Mg 2Ni and cast Mg 2Ni. Mg 1.9Ti 0.1Ni absorbs more than 3 wt% H 2 in 2000 s at 423 K while the mechanically alloyed and the cast Mg 2Ni do not form hydride at this temperature. Partial substitution of Mg by Ti reduced the activation energy of desorption from 69 kJ mol −1 for nanocrystalline Mg 2Ni to 59 kJ mol −1 for Mg 1.9Ti 0.1Ni.

Electrochemical characteristics of an amorphous Mg0.9V0.1Ni alloy prepared by mechanical alloying

Electrochemical characteristics of an amorphous MgNi alloy with Mg partially substituted by V were investigated. A Mg0.9V0.1Ni alloy prepared by mechanical alloying (MA) exhibited much better cycle life than MgNi alloy. It was found that the partial substitution of Mg in MgNi with V could suppress the formation of Mg(OH)2 on the alloy surface during the charge–discharge cycling in alkaline solution. This may have unveiled an important factor to improve cycle life of the Mg-based alloy for use in nickel–hydrogen batteries.

Mass-spectrometric investigation of the stabilities and structures of Mn-O and Mn-Mg-O clusters.

Time-of-flight mass spectrometry was used to investigate Mn-O and Mn-Mg-O clusters produced by a gas aggregation technique. The primary stoichiometries observed were (MnO${)}_{\mathit{x}}^{+}$ (x=1--13) and (MnO${)}_{\mathit{x}}$${\mathrm{O}}^{+}$ (x=4--22) clusters, and also these series with partial substitutions of Mg for Mn. The mass spectral abundance patterns suggest that the most stable structures for the stoichiometric clusters are stacks of rings composed of (MnO${)}_{3}$ units, and that the oxygen-rich clusters prefer these structures with a single Mn atom vacancy. The partial substitution of Mg for Mn in the clusters appears to have little effect on these structural preferences. Interesting similarities and differences are observed when the stoichiometric and structural properties of these clusters are compared with the properties of the bulk materials, and also alkaline-earth oxide clusters.

Compositional variation in högbomites from north Connemara, Ireland

AbstractHögbomite occurs in two contrasting mineral assemblages within the Currywongaun-Dough-ruagh intrusion of north Connemara: a cordierite-rich pelitic xenolith and an orthopyroxenite. In the latter, högbomite and green spinel form blebs within magnetite-ilmenite grains. The högbomite displays significant compositional variation from grain to grain: TiO2 (3.0–6.3%), FeO (21.6–21.3%), MgO (10.0–7.5%), ZnO (3.6–2.4%). This chemical heterogeneity appears to represent variable degrees of partial substitution of Mg and Zn by Ti, in the replacement of spinel by högbomite. By contrast, in the cordierite-hornfels, the högbomite compositions are more notably enriched in iron: TiO2 (4.7–7.0%), FeO (29.6–24.3%), MgO (4.2–6.2%), ZnO (2.7–2.1%). This iron-rich högbomite appears to have formed primarily by interaction between opaque ore and adjacent cordierite, rather than by replacement of spinel.Two high-grade metamorphic episodes appear to be necessary for högbomite growth, one determining chemical composition and the other appropriate physical parameters. In the Connemara occurrences thermal metamorphism and partial melting, coupled with contamination of the surrounding magma, controlled the formation of mineral assemblages rich in Fe, Mg, Al, Ti, and Zn. Emplacement of the intrusion was accompanied by amphibolite facies regional metamorphism and it is to this metamorphic event that the growth of högbomite may be attributed.

Pressure DSC study of the hydrogenation and dehydrogenation of some intermetallic compounds Mg2Ni

Pressure differential scanning calorimetry (DSC) has been applied to a study of the hydrogenation and dehydrogenation of some intermetallic compounds Mg 2 Ni. The effects of hydrogen pressure, pulverized compound's sizes as well as chemical composition of the compound, partial substitution of Mg in Mg 2 Ni by Al, and the second phase MgNi 2 dispersed in Mg 2 Ni on the hydrogenation and dehydrogenation of the intermetallic compound Mg 2 Ni are elucidated in some detail by this experimental technique. It is emphasized that a pressure DSC is available as a rapid and convenient experimental means for assessing hydrogen absorption and desorption properties of hydrogen storage materials.

Etude d'alliages de composition CeMg 11M (M = V, Cr, Mn, Fe, Co) et de leur application au stockage de l'hydrogene

Partial substitution of Mg in CeMg 12 by M = V, Cr, Mn, Fe and Co has been investigated for the composition CeMg 11M. For each system at least two phases are obtained. The absorption-desorption hydriding cycles have been compared with that of CeMg 12 itself. Although the hydriding speed is not strongly modified by the presence of the 3d-element, dehydriding is much enhanced. Thanks to their performances and their high weight content, such alloys may be used for hydrogen storage.