Effect of high-energy milling on hydrogen desorption and the structure of mixtures of Zr-containing materials

Mass-spectrometric investigations of hydrogen liberation from the mixture of powders 3ZrO_0.2H_x + ZrFe₂, the overall composition of which corresponds to Zr₄Fe₂O_0.6H_x, after its treatment by ball milling for 5 and 50 h show a substantial dependence of hydrogen desorption on the time of mechanical treatment. X-ray phase analysis demonstrates a significant disordering of the structure of components after high-energy ball milling. The combination of mechanical treatment and hydrogen desorption from the prepared mixtures does not lead to the formation of the Zr₄Fe₂O_0.6 intermetallic phase as was observed during desorption-recombination in the HDDR process. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 6, pp. 55–59, November–December, 2005.     

Hydrogenation of oxygen-stabilized Zr3NiOx compounds

It is shown that oxygen-stabilized compounds Zr₃NiO_x (x=0.4, 0.6, 0.8, 1.0) interact with hydrogen at ambient temperature and pressure forming saturated hydrides with a filled Re₃B-type structure. The hydrogen storage capacity decreases with increasing oxygen content from 6.65 H/f.u. for Zr₃NiO_0.4 down to 5.58 H/f.u. for Zr₃NiO_1.0. A slight decrease of the crystal lattice parameters of the parent compounds and a substantial increase of these parameters for the saturated hydrides were observed with increasing oxygen content. The partial hydrogen-induced lattice expansion, ΔV/at. H, increases from 2.333 ų for Zr₃NiO_0.4H_6.65 to 3.047 ų for Zr₃NiO_1.0H_5.58. Joint Rietveld refinement using X-ray and neutron powder diffraction data showed a distribution of deuterium atoms on similar positions as in oxygen-free Zr₃FeD_x and Zr₃CoD_x. The oxygen atoms move during deuteration from the octahedral site to one trigonal bi-pyramidal and two tetragonal interstices that are fully occupied in the saturated deuterides jointly by deuterium and oxygen. After deuterium desorption the oxygen atoms fully return to the initial octahedral site.     

Ti–Ni alloys as MH electrodes in Ni–MH accumulators

In hydrogen solid–gas reaction at 300 K and 1 bar, the hydrogen content for Ti_3.87Ni_1.73Fe_0.7O_x (0.2≤ × ≤0.8) alloys was in range 1.93–0.05 (Cwt.H,%), and discharge capacity of 360–235 A h/kg was achieved accordingly. The ΔHH₂$\Delta H_{{\text{H}}_2}$ and ΔSH₂$\Delta S_{{\text{H}}_2}$ values of −32.29 kJ mol⁻¹ and −111.04 J mol⁻¹ K⁻¹, respectively, for Ti_3.87Ni_1.73Fe_0.7O_0.5 alloy were obtained using experimental PCT relations, where hysteresis effect was only slightly visible. The half-cell potentials (vs. Hg/HgO) of metal hydride (MH) electrodes based on Ti_3.87Ni_1.73Fe_0.7O_x (0.2≤ ×≤ 0.8) alloys were calculated.     

Effect of the modification of metal-hydride electrodes based on Ti2Ni alloys on their discharge characteristics

We have developed a new computerized PGStat-8 device for the high-cycle charge-discharge of electrodes under galvanostatic or potentiostatic conditions and, with its help, have investigated the charge-discharge characteristics of metal-hydride electrodes based on Ti₂Ni-type alloys. We show the effect of partial replacement Ti → Zr or V and Ni → Co or Cu, modification with oxygen, homogenizing annealing, polymeric addition, and metallic binder on the discharge capacity and cyclic stability of the prepared metal-hydride electrodes. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 5, pp. 56–64, September–October, 2006.     

Investigation of Ti(Zr–Ni) Hydrogen-Sorbing Alloys as Electrode Materials for Nickel–Metal-Hydride Storage Batteries

We studied cyclic charge–discharge characteristics of partially substituted and oxygen-containing derivatives of a Ti₂Ni alloy by using specially designed equipment based on PI-50-1 potentiostats and a computer. For Ti_3.8Zr_0.2Ni₂O _x alloys, a twofold increase in the discharge capacity was detected as the oxygen content increased from x = 0 to x = 0.3. It was established that the effect of the hydrogenation–desorption–disproportionation–recombination process on the homogeneity of the Ti4Ni2O_0.3 alloy and its electrochemical charge–discharge parameters in alkaline electrolytes is positive.     

Influence of Oxygen Modification and Alloying on the Charge–Discharge Characteristics of Metal-Hydride Electrodes Based on Ti2Ni

An improvement of discharge capacity of metal-hydride electrodes based on hydrides of Ti_4 – x Zr _x Ni₂O _y alloys (0.2 x 0.6; 0.2 y 1.0) was shown during simultaneous partial Ti Zr substitution and oxygen modification. The maximal value of C _p (311 A · h · kg^–1) was experimentally found for a metal-hydride electrode based on Ti_3.6Zr_0.4Ni₂O_0.6H_5.2. High cyclic stability was shown for the oxygen-containing Ti_3.6Zr_0.2V_0.2Ni₂O_0.3 and Ti_3.8V_0.2Ni₂O_0.3 alloys alloyed with vanadium.     

Synthesis and Determination of the Crystal Structure of Hydrides of Er(M,V)<Subscript>2</Subscript>, where M = Fe or Co,Compounds

We study the process of formation of the Laves phases AB₂ in Er(M, V)₂ (M = Fe or Co) systems and determine their hydrogen-sorption properties. The crystal structure of parent compounds and their saturated hydrides is analyzed by the X-ray diffraction method. It is shown that these compounds absorb hydrogen at pressures of 0.1– 0.12 MPa without amorphization. The formation of the ErFe₂ hydride is accompanied by the transformation of a cubic MgCu₂-type structure into a trigonal TbFe₂-type structure. Even an insignificant substitution of Fe with V or Co leads to an increase in the hydrogen-sorption capacity and prevents the changes in the crystal structure.__________Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 40, No. 6, pp. 62–66, November–December, 2004.     

Characterization of metal hydrides by in-situ XRD

In-situ synchrotron radiation powder X-ray diffraction (SR-PXD) technique is a powerful tool to gain a deeper understanding of reaction mechanisms in crystalline materials. In this paper, the implementation of a new in-situ SR-PXD cell for solid–gas reactions is described in detail. The cell allows performing measurements in a range of pressure which goes from light vacuum (10⁻² bar) up to 200 bar and temperatures from room temperature up to 550 °C. The high precision, with which pressure and temperature are measured, enables to estimate the thermodynamic properties of the observed changes in the crystal structure and phase transformations.