E. Grigorova

Addition of nanosized Cr2O3 to magnesium for improvement of the hydrogen sorption properties

Abstract The combination of (i) the catalytic effects of Cr2O3, (ii) reactive mechanical grinding (RMG), and (iii) nanosize particles allow a huge improvement in the sorption properties of magnesium. For short milling duration, the absorption kinetics were already as good as that reported for nanocrystalline (Mg+Cr2O3) mixtures. The desorption process is also improved but not in a similar manner. It is assumed that the RMG of nanosized particles of Cr2O3 results in the formation of some Cr atoms in the mixture which greatly influence the sorption behavior.

Hydrogen sorption properties of an Mg-Ti-V-Fe nanocomposite obtained by mechanical alloying

Abstract The absorption–desorption characteristics with respect to hydrogen of a magnesium-based nanocomposite obtained by high-energy ball milling have been investigated. The composite contains 5 wt.% (∼3at.%) Ti, 10 wt.% (∼5.5 at.%) V and 10 wt.% (∼5 at.%) Fe, of which the former two transition metals only form a binary hydride. It has been shown that at 623 K the composite may be hydrided up to a very high absorption capacity whose values remain appropriate for practical purposes even at much lower hydriding temperatures. Part of the iron present in the composite has been found to interact with magnesium and hydrogen under the hydriding conditions, the ternary hydride Mg 2 FeH 6 being formed. Its presence in the composite-hydrogen system has been assumed to be responsible for the reduced rate of hydrogen desorption from the particle surfaces and for some peculiarities of the composite behaviour during hydriding.

Hydrogen sorption properties of the nanocomposites Mg–Mg2Ni1−xFex

Abstract The hydrogen sorption properties of the composites 85 wt.% Mg–15 wt.% Mg 2 Ni 1− x Fe x ( x =0, 0.1 and 0.3) prepared by high-energy ball milling were studied. It was shown that the presence of a Mg 2 Ni 1− x Fe x additive significantly improved the kinetics of hydrogen absorption and desorption of magnesium, the absorption capacity remaining sufficiently high even at temperatures between 423 and 573 K. The catalytic effect of the Mg 2 Ni 1− x Fe x intermetallics was explained as due to the formation of a second hydride, Mg 2 NiH 4 , to the appearance during the mechanical alloying of defects facilitating the formation of hydride nuclei and to the presence of Ni and Fe clusters on the surface of nanocomposite particles.

Hydrogen sorption properties of the nanocomposite 90 wt% Mg2Ni+10 wt% V

Abstract The absorption–desorption characteristics of the nanocomposite 90 wt% Mg2Ni+10 wt% V obtained by mechanical alloying under argon or hydrogen atmosphere have been investigated. The effect of vanadium, the activation time and the gas medium during the milling on these characteristics have been shown. The absorption capacity of the sample activated for 30 min under argon is found to be 1.94% at T=573 K and P=1 MPa, whereas for the hydrogen-activated sample the capacity is 2.3% and some absorption is observed even at room temperature. The hydrogen sorption properties of the Mg2Ni+10% V composite are compared with those of an alloy with the composition Mg2Ni0.9V0.1.

Hydrogen sorption characteristics of magnesium-based composites with addition of Mg2Ni0.7Co0.3 and graphite

AbstractMagnesium-based composites of 75 wt% Mg — (10, 15, 20) wt% Mg2Ni0.7Co0.3 — (15, 10, 5) wt% C mechanically activated for 30 min under argon in a planetary mill, were obtained. Their absorption-desorption characteristics were investigated under a pressure P = 1 MPa and temperatures of 623, 573, 473, 423 and 373 K. Desorption was carried out at 623 K and 573 K and a pressure of 0.15 MPa. All the three composites showed improved hydriding kinetics as compared to pure magnesium. However, the desorption temperature was somewhat higher than needed for practical application.