S. N. Klyamkin

Interaction of intermetallic compounds with hydrogen at pressures up to 250 MPa: the LaCo5−xMnx-H2 and CeNi5−H2 systems

Abstract A new method has been proposed for the synthesis and thermodynamic study of intermetallic hydrides at pressures of gaseous hydrogen up to 250 MPa. From preliminary experiments on hydrogen compressibility and consideration of available p - V - T data for hydrogen at high pressures we have chosen a modified van der Waals equation giving a calculation error of 0.1%–0.5% or less. Absorption and desorption isotherms for the LaCo 5− x Mn x -H 2 ( x −0.05) and CeNi 5 −H 2 systems were measured at temperatures from 195 K up to room temperature. The highest hydrogen content obtained in a hydride composition of LaCo 5− x Mn x does not exceed 8 at. H per formula unit, and for the high pressure plateau ΔH abs = ΔH des =14.4 kJ (mol H 2 ) −1 and ΔS abs = ΔS des =110.2 J K −1 (mol H 2 ) −1 . In the CeNi 5 -H 2 system the existence of a single plateau and considerable hysteresis were observed.

Thermodynamic particularities of some CeNi5-based metal hydride systems with high dissociation pressure

Abstract The thermodynamic behaviour of the CeNi 5 H 2 , Ce 0.8 La 0.2 Ni 5 H 2 and Ce 0.8 La 0.2 Ni 4.7 Cu 0.3 -H 2 systems during a few activation absorption-desorption cycles was studied by means of high gaseous pressure technique. P-C isotherms in the temperature range from 273 to 353 K were measured and thermodynamic parameters for hydride formation and decomposition reactions were calculated. For all studied systems the same hydrogen capacity (6.5–6.8 H atoms per AB 5 unit at 1000 atm and 296 K) and the same isotherm shape with a long nearly horizontal plateau and very large hysteresis were obtained. The change in alloy composition in the range CeNi 5 →Ce 0.8 La 0.2 Ni 5 →Ce 0.8 La 0.2 Ni 4.7 Cu 0.3 led to an increase in plateau length and a decrease in hysteresis factor P abs /P des . The hysteresis factor also decreased considerably after two or three activation cycles, by 4–8 times as compared with the first cycle. This phenomenon was connected not only with an absorption pressure decrease but also with a significant increase in desorption pressure. The relative change P 1 /P act in equilibrium pressure during the activation did not depend on alloy composition for the absorption reaction, but in the case of desorption it decreased with partial substitution of Ce and Ni by La and Cu correspondingly.

Hydrogen interaction with RNi3 type intermetallic compounds at high gaseous pressure

Pressure-composition isotherms for CeNi 3 -H 2 , CeNi 2.2 Mn 0.8 -H 2 and ErNi 3 -H 2 systems were measured at pressures up to 2000 atm and at temperatures from - 78°C to 23°C. New hydride phases RNi 3 Hs 5.5-5.6 were synthesized and characterized by X-ray diffraction. Thermodynamic parameters of formation-decomposition reactions at low temperature for intermediate ErNi 3 H 4 phase were calculated as ΔH = 23.8 kJ mol -1 and ΔS = 103 J K -1 mol -1 . The phenomenon of irreversible hydrogen absorption at high pressure was found for all studied systems. Thermal desorption peculiarities for CeNi 3 H x and ErNi 3 H x hydrides were determined.

Preparation and properties of hydrogen-storage composites in the MgH2-C system

The hydriding properties of magnesium have been studied at temperatures from 670 to 720 K and pressures from 19 to 55 MPa. The results suggest that the hydrogen pressure and hydrogen absorption/desorption cycles influence the nucleation process in the Mg-H2 system. Using mechanical activation of MgH2 + graphite and MgH2 + graphene nanofiber (GNF) mixtures, we have prepared MgH2/graphite and MgH2/NGF composites. Investigation of their hydriding properties has shown that mechanical activation markedly accelerates hydrogen sorption/desorption processes and reduces the thermal stability of the material compared to unmilled magnesium hydride. The mechanisms of hydrogen desorption from the composites in different stages of their thermal decomposition are analyzed.

Radiation-Resistant Erbium-Doped Fiber for Spacecraft Applications

Radiation-induced absorption and lasing efficiency of a hermetically coated erbium-doped fiber saturated with molecular hydrogen are studied. It is shown that H2-loading of hermetically coated erbium-doped fibers prolongs their service time in space more than in 5 times, making such fibers promising for space applications.

Effect of substitution on F.C.C. and B.C.C. hydridephase formation in the TiCr2–H2 system

Abstract Phase transformations of TiCr 1.8 , ZrCr 2 , Ti 0.9 Zr 0.1 Cr 1.8 , Ti 0.7 Zr 0.3 Cr 1.8 and TiCr 1.7 Fe 0.1 intermetallic compounds during their interaction with hydrogen at pressuresfrom 1 to 200 MPa and temperatures of 195 and 295 K are studied. Formation of three types ofhydride phases are stated by X-ray diffraction method: (I) hexagonal Laves phase preserving theMgZn 2 structure of the initial intermetallic, (II) F.C.C. phase of CaF 2 structure type which can be considered as a solid solution in the pseudobinary TiH 2 -CrH 2 system and (III) B.C.C. phase with W-structure type—high temperature β solution in the metallic Ti–Cr system stabilized by hydrogen. It was shown that partialsubstitution of titanium by zirconium up to 30% did not change the general scheme of phasetransformations, while the addition of iron suppressed the formation of phases (II) and (III) in allexperimental pressure and temperature ranges. The conditions of formation, X-ray parameters andthermal stability have been determined for synthesized hydride phases in the TiCr 2 -H 2 and substituted systems.

Influence of MIL-101 Doping by Ionic Clusters on Hydrogen Storage Performance up to 1900 Bar

Ultra-high-pressure hydrogen-storage performance (up to 1900 bar) was investigated for mesoporous chromium terephthalate MIL-101 and its inclusion compounds containing ionic clusters [Re(4)S(4)F(12)](4-) and [SiW(11)O(39)](7-) within the porous framework. The maximum specific hydrogen uptake values (total) for MIL-101 are 12.3 (at 81) and 7.2 wt. % (at 293 K). Such unique measurement conditions allowed us to identify the density of the absorbed hydrogen directly from the excess sorption isotherm curves. The corresponding density values were found to be almost comparable at low temperature, but significantly different at ambient temperature, which indicated an increase of more than double in the number of hydrogen binding sites in the case of the inclusion compounds with rhenium clusters.

Effect of substitution on hysteresis in some high-pressure AB2 and AB5 metal hydrides

Abstract Ti 0.95 Zr 0.05 Cr 1.2 Mn 0.8− x V x –H 2 ( x =0, 0.05 or 0.1), Ti 0.95 Zr 0.05 Cr 1.2 Mn 0.8− y Co y –H 2 ( y =0, 0.1 or 0.2) and Ce 0.8 La 0.2 Ni 5− z Co z –H 2 ( z =0, 0.5, 1.0 or 1.5) systems were studied experimentally in order to (a) find suitable alloys for high-pressure applications, and (b) gain insight into the reasons for the hysteresis and its reduction due to certain partial substitutions. A special volumetric pressure–composition isotherm (PCI) measurement technique at high pressures (up to 400 bar in this case), pressure differential scanning calorimetry (PDSC), and X-ray diffractometry (XRD) of both starting alloys and SO 2 - (or air-) poisoned high-pressure hydrides were applied. Practically hysteresis-free high-pressure alloy–hydrogen systems with good PCI plateau properties were found, e.g. Ti 0.95 Zr 0.05 Cr 1.2 Mn 0.75 V 0.05 –H 2 . Furthermore, it was shown that an intermediate hydride phase in the Ce 0.8 La 0.2 Ni 3.5 Co 1.5 –H 2 system exists, which explains the remarkably reduced hysteresis compared to the less or non-substituted systems. Finally, an experimental correlation between hysteresis and discrete unit cell volume expansion between coexisting phases was displayed. It suggests that the volume expansion is a major reason for the hysteresis, but more experimental data needs to be collected.

Effect of Mechanical Activation on the Reaction of Magnesium Hydride with Water

The effect of the parameters of mechanochemical activation of magnesium hydride and MgH2-graphite binary compositions on the parameters of materials and their hydrolytic activity has been studied. It is concluded that mechanochemical treatment increases the reactivity of magnesium hydride in its reaction with water. Graphite provides an additional activating effect during the mechanochemical treatment of MgH2. A deformation dose of 20 kJ/g was determined to be the optimum one for achieving the highest reactivity in the hydrolysis reaction with the formation of MgH2-graphite composites. As a result of the hydrolysis of such materials, up to 970–1280 mL hydrogen per composite gram is evolved in 40 min of the reaction with water without an additional change in the solution acidity.

Mechanochemical synthesis and hydrogen sorption properties of nanocrystalline TiFe

The equiatomic intermetallic compound TiFe has been prepared by elemental mechanochemical synthesis in a planetary ball mill from Fe and Ti powders. The structural and phase transformations during synthesis were followed using X-ray diffraction. The reaction of the synthesized compound with hydrogen was studied volumetrically. The results demonstrate that the hydrogen capacity of the mechanochemical TiFe is 1.2 wt % at 2.5 MPa. Its absorption isotherm has an extended plateau in the range 1.6–1.7 MPa at room temperature.