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The structure of the V–15Ni at.% alloy before and after hydrogen permeability tests was investigated by means of XRD and SEM with EDS analysis. We have found that decomposition of supersaturated V-based solid solution with variable Ni content occurred during testing. The volume fraction of the solid solution decreased and the fraction of V3Ni phase increased during permeability testing, thus bringing the alloy to nearly equilibrium. The membrane without Pd coating showed satisfactory hydrogen fluxes with a significant impact of the surface dissociation rate of hydrogen. The shape of hydrogen permeation curves at the downstream side of the membrane at various temperatures was unusual. We attribute it to the high concentration of dissolved hydrogen in the metal lattice and its effect on the hydrogen diffusivity and solubility. In addition, the multiphase structure with non-uniform distribution of nickel both between the phases and within the BCC solid solution (and, consequently, different hydrogen concentrations) may cause dilatation or compressing effect on neighbouring micro-volumes of the alloy.

We study the process of hydrogen release from magnesium hydride under the conditions of uniaxial pressing in a vacuum at room temperature up to pressures of about 2.4 ton/cm2. It is shown that the desorption of hydrogen occurs under loading. The amount of hydrogen almost linearly depends on the applied pressure. The measured coefficient is 5 ·10– 3 wt.%· cm2 /ton.

Speed-up of thermal decomposition of magnesium hydride due to uniaxial pressing, including pressing in presence of nickel catalyst, was studied by barometry, SEM, DSC, XRD methods, and using mathematical modeling. Pressing even with no catalyst is shown to hasten the hydrogen desorption. The most probable reason for this is the formation of multiple defects in crystal lattice. They can serve as nucleation centers: metal nuclei significantly hasten hydrogen desorption. Besides, metal magnesium not converted to the hydride during the synthesis stage can possibly appear at surface. Adding nickel powder before pressing hastens dehydriding process even more. Comparing hydrogen evolution curves for samples with different amount of nickel allowed to propose the probable mechanism of hydrogen evolution. It is based on description of reactions of hydrogen desorption and hydride decomposition and of the metal-hydride phase morphology change due to these reactions. We develop a mathematical model in form of ordinary differential equations that fits the experimental data well. The model is based on conservation and symmetry assumptions. The fitting allowed to evaluate rate parameters of hydride phase decomposition.

We have studied the activation of magnesium hydride decomposition by means of its pressing with a catalyst. It is established that pressing leads to the formation of metal nuclei, which favor a decrease in the temperature threshold of magnesium hydride decomposition. The introduction of catalytic additives also reduces the temperature of dehydrogenation. The most effective in this respect was found to be the addition of nickel powder.

The hydrogen permeation technique in the surface-limited regime (SLR) was first used to study the isothermal decomposition of zirconium hydride. It is shown that under isothermal conditions, the hydrogen terminal solid solubility in the α-phase for hydride precipitation (TSSp) and dissolution (TSSd) differ only by 6%, in contrast to the 20–30% indicated in the available literature. It is demonstrated that even the minimum heating/cooling rate (1 C/min) used in the traditional methods of studying TSSp and TSSd is too high to exclude the effect of kinetics on the results obtained.

The synthesis procedure of a thin aluminum-hydrogen film on a silicon substrate is described and its result thoroughly investigated by a number of experimental methods. The reactive sputtering deposition was carried out to obtain a structure containing aluminum hydride. The resulting film has characteristic non-metallic properties, though according to thermal desorption studies its hydrogen content is close to AlH1.1, which is lower than stoichiometric aluminum hydride AlH3. Thermal desorption of hydrogen differs significantly from that of AlH3 powder as it has not one but several peaks. According to transmission electron microscopy the film is mostly amorphous but contains crystalline phase. Our interpretation of the experimental data suggests that some hydride phase microcrystals were formed as the film was deposited, but most hydrogen was stored inside the film without forming a crystalline structure in both bounded and unbounded states. The luminescent properties of the synthesized film are similar to aluminum hydride, and it can be concluded that the amorphous Al-H structure of the synthesized film shows resemblance with AlH3 crystals populated with hydrogen vacancies.

We studied cathodoluminescence and photoluminescence of α-AlH3 – a likely candidate for use as possible hydrogen carrier in hydrogen-fueled vehicles. Luminescence properties of original α-AlH3 and α-AlH3 irradiated with ultraviolet were compared. The latter procedure leads to activation of thermal decomposition of α-AlH3 and thus has a practical implementation. We showed that the original and UV-modified aluminum hydride contain luminescence centers ‐ structural defects of the same type, presumably hydrogen vacancies, characterized by a single set of characteristic bands of radiation. The observed luminescence is the result of radiative intracenter relaxation of the luminescence center (hydrogen vacancy) excited by electrons or photons, and its intensity is defined by the concentration of vacancies, and the area of their possible excitation. UV-activation of the dehydrogenation process of aluminum hydride leads to changes in the spatial distribution of the luminescence centers. For short times of exposure their concentration increases mainly in the surface regions of the crystals. At high exposures, this process extends to the bulk of the aluminum hydride and ends with a decrease in concentration of luminescence centers in the surface region.

We present a distributed mathematical model and fit discharge curves of Ni–MH anode made of new alloy La 2 MgNi 9 . Conditions justified the single-particle approximation with the shrinking core morphology of the hydride phase. We used the connection between voltage on the MH electrode and hydrogen concentration in the solid solution near the electrolyte facing surface. This connection is based on shift of the Fermi energy of the metal due to hydrogen dissolution. The model takes hydrogen diffusion and free phase boundary into account. It can be built into more general models describing discharge of Ni–MH rechargeable batteries.

In present work we have developed a theoretical model for the description of the electrochemical discharge process in the metal hydride anodes of the metal hydride batteries at various current densities. The model is based on the description of the assembly of the spherically shaped metal hydride particles where the process of electrochemical discharge is fit using a shrinking core model, with a shell of the H storage alloy growing inside the particle by decreasing volume of the internal metal hydride core. The model accounts results of the D.O.S. calculations for La2MgNi9 intermetallic alloy and has been tested for this metal hydride anode material having an electrochemical discharge capacity of 400 mAh/g and hydrogen storage capacity of 13 at.H/f.u. La2MgNi9. It allows to quantitatively describe kinetic behaviors of the electrode at various applied current densities and to estimate the diffusion coefficient for hydrogen and equilibrium content of H in the solid solution domain of hydrogen in La2MgNi9. This model has a general applicability and can be used for the optimization of the materials and the electrodes of the metal hydride rechargeable batteries at high current densities.

We investigated the mechanism of activation of α-AlH 3 powder decomposition by irradiation with ultraviolet (UV) light using barometry, photoluminescence (PL), cathode luminescence (CL) and X-ray diffraction (XRD) methods. Exposing the samples under a mercury lamp through the filters we have shown that only the line, corresponding to the energy of 4.88 eV, leads to activation, whereas the spectral lines of lower energy are ineffective. XRD shows that after continued UV activation the aluminum clusters with metallic properties are formed on the surface of the AlH 3 powder particles at room temperature. The analysis of results of performed calculations of the absorption spectrum of the perfect crystal α-AlH 3 using DFT method showed that hydrogen vacancies are involved in activation by UV light. Studying of dynamics of CL and PL spectra at different UV expositions permitted to suggest the following mechanism of activation. Absorption of a photon implies that vacancy captures an electron from a neighboring hydrogen atom. Hydrogen atom then can leave its regular position in the lattice and form a new vacancy next to the first. Clustering of vacancies occurs. Continued UV activation is accompanied by merging of vacancies, which deprives the aluminum atoms of hydrogen bonds connecting them. Thus the aluminum clusters with metallic properties are formed.

The aim of the research was to understand decomposition of hydrides of metals and determine the most significant limiting reactions. We used functions that describe real physical processes, such as decomposition of hydride phase, desorption and diffusion of hydrogen, and morphology of phases. Dividing hydride materials to two classes depending on the type of bonding (metallic or non-metallic) allowed to explain details of kinetics of dehydriding. We show that for decomposition of non-metallic hydrides morphology of “nucleation and growth” is typical; while for metallic ones the “shrinking core” morphology is more common. In both cases hydrogen diffuses from the hydride-metal boundary to the outer surface through the metal phase rather quickly, so diffusion does not influence on the decomposition kinetics. The most probable limiting factor is the rate of hydrogen desorption from the metal phase. For the “shrinking core” morphology rate of hydride decomposition can also influence on the kinetics during the final stages of the process.

We investigated activation of thermal dehydriding of α-AlH3 crystal by preliminary irradiation by ultraviolet light using thermal desorption spectroscopy, barometry, and cathode luminescence methods. It is shown that hydrogen vacancies appear due to irradiation; they serve as points where metal nuclei probably appear, so dehydriding becomes significantly faster. Possible explanation of transformation of hydrogen vacancies to metal phase nuclei is suggested: new vacancies are more likely to appear near the first one compared to remote places. Using density functional theory method we calculated the electronic structure of stoichiometric α-AlH3 and α-AlH3 with a hydrogen atom removed from a regular lattice site with a vacancy in place of it. It is suggested that an appearance of a new vacancy near the first vacancy needs less energy compared to the first one. From cathode luminescence data we see that appearance of vacancies can also be activated thermally. The model of hydrogen desorption from α-AlH3 activated by UV light is suggested and kinetic parameters of desorption are evaluated.

Kinetics of dehydrogenation was studied using isothermal barometry, TDS and SEM methods. Two stages of the decomposition process are considered: incubation preceding the formation of metallic nuclei on the surface of the particle and hydrogen evolution via these metallic regions serving as facilitating channels for desorption. Duration of the first stage depends on the temperature of the sample. Relationship with material's electronic band structure is discussed. Kinetics of the second stage is controlled by two reactions: desorption of the hydrogen molecules from the surface and shift of the metal-hydride interphase in the bulk. Physical mechanisms of decomposition with detailed reaction kinetics are proposed and kinetic parameters are evaluated.

New approach to analyse hydride decomposition kinetics operating with integral morphological parameters as well as kinetic parameters of possible rate-limiting reactions (nucleation, desorption and reaction at interface) is proposed. Morphology of new phase growth in powder particle is described in terms of specific values of new phase volume, outer surface occupied by new phase, interface area and their interrelations (“morphological trajectories”). The approach describes H-release kinetics for free-form shape of particles and growing nuclei. The applicability of the approach is limited by the requirements of fast enough H-diffusivity in metal areas of powder particles and of nucleation at the outer surface of particles. Alane powder completely meets these requirements. It was found that the rate-limiting step is the reaction at the interface with activation energy 104 kJ/mol. Morphology of the transformation depends on experiment conditions: the higher is reaction temperature, the smaller is quantity of new phase nuclei.

A method of thermocycling in a hydrogen medium for studying the kinetics of the interaction between hydride-forming metals and hydrogen is proposed. The method is applied to the titanium powder with a grain size of 15–20 μ m. Thermocycling curves were obtained in a wide range of temperatures and concentrations for α - and β -titanium. Evaluations of the kinetic parameters of absoprtion and desoprtion as well as the heat of sorption in α - and β -titanium are presented.

Erbium was used as a model hydride-forming metal to study the possibility of applying thermal desorption spectroscopy (TDS) to research into hydride decomposition. The possibility of varying heating rates and final temperatures makes TDS acceptable for providing experimental information about the kinetics of decomposition. Discrimination of models and evaluation of rate constants were performed by fitting computer-simulation derived curves to experimental ones. The most probable models have boundary-value problems in which the rates of decomposition, desorption and migration of hydrogen are taken into account. The movement of an interface between hydride and solid solution of hydrogen is determined by all these reactions.

In the presented research, a new algorithm of detection and analysis of non-stationary phases (NSPh), characterizing sudden changes in heart rate variability (HRV) parameters was used. Physiological reactions of air traffic controllers during the performance of training scenario were estimated. 39 participants - 14 experienced air traffic controllers and 25 students performed a 40-minute scenario, which included 3 stressful incidents: a rapid increase in air traffic density, low fuel level and plane engine failure. Students also performed the scenario after brief training. The results have shown that as expertise grows respondents show a significant decrease in duration and change in patterns of non-stationary phases of heart rate arising in response to the stressful incidents. These changes of parameters of non-stationary phases are connected with increased efficiency of air traffic controllers' cognitive performance in stressful conditions. The research has illustrated that the analysis of non-stationary phase parameters complements classical HRV measures and may be used for assessment of physiological responses of operators in Augmented Cognition applications.