The reaction of lithium hydride (LiH) powder with pure water vapor (H2O and D2O) was studied by thermogravimetry and in situ infrared spectroscopy at 298 K over a large pressure range. The mean particle size of LiH is around 27 mu m. At very low pressure, the hydrolysis starts with the formation of lithium oxide (Li2O). Then, both Li2O and lithium hydroxide (LiOH) are formed on increasing pressure, thus, creating a Li2O/LiOH bilayer. The reaction takes place through the consumption of LiH and the formation of Li2O at the LiH/Li2O interface and through the consumption of Li2O and the formation of LiOH at the Li2O/LiOH interface. Above 10 hPa, only the monohydrate LiOH center dot H2O is formed. This hydration reaction of LiOH into LiOH center dot H2O occurs at a lower pressure (8 hPa) after the first hydration-dehydration cycle. The hydrolysis mechanism proposed in this paper suggests that the diffusion of ionic species across the intermediate Li2O layer is the rate limiting step of the reaction. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Hydrolysis of LiH at room temperature and under low relative humidity (RH < 2%) is studied by manometry working with heavy water either in closed (variable water vapor pressure) or open (constant water vapor pressure) system. Products of the reaction are characterized by XRD and FTIR. It is shown for the first time that the hydrolysis reaction occurs in two steps: first water is adsorbed on the LiH surface and then the hydrolysis reaction starts. In open system, for relative humidity lower than 0.04% only the formation of Li2O is observed while for higher moisture the reaction continues with the production of LiOD. The reaction rate is however extremely low and only a very small amount of LiH is transformed. The kinetic can be well predicted by the model of core shrinking limited by the diffusion through the layer of Li2O and/or LiOD surrounded LiH particles. For practical application, it is concluded that if LiH is stored under controlled humidity lower than 0.04% (40 ppm) there is no major risk to form LiOH in significant amount.

The biphasic product CoS2 + Co(OH)(2) obtained by oxidation of cobalt sulfide is known to trap hydrogen at room temperature and low pressure according to a balanced reduction equation. Adding various inorganic compounds to this original absorber induces their reduction by hydrogen in the same conditions at a significant rate: (i) excess cobalt hydroxide is reduced to metallic cobalt; (ii) nitrate ions are reduced to ammonia; (iii) sulfur and sodium thiosulfate are reduced to H2S or NaHS and Na2S, respectively. Without a hydrogen absorber these inorganic compounds are not reduced by H-2, suggesting synergetic effects involving H-2 and the hydrogen absorber. Amorphous cobalt polysulfide, CoS5, is also reduced by hydrogen at room temperature and releases H2S gas. In the presence of a base to neutralize H2S gas, the reaction rate is initially slower than with the CoS2 + Co(OH)(2) mixture due to the higher stability of polysulfide chains but the H-2 trapping yield is improved, making CoS5 a good candidate for H-2 trapping. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

The hydrolysis reaction of LiH powder has been investigated in order to determine the products, rates and mechanisms of this reaction and the influence of the experimental parameters. Raman spectroscopy, X-ray diffraction and gravimetric analysis were used. It was shown that the product of hydrolysis was the hydroxide of lithium (LiOH) for low partial pressure of water (≈50Pa) and LiOH·H2O for a higher partial pressure of water (>2000Pa). Moreover, data obtained using gravimetric analysis inside a glove box containing a controlled partial pressure of water (500ppmv/50Pa at 25°C) were used to determine the rate of the reaction versus particle size. The experimental results were consistent with the shrinking core model showing that initially, the conversion rate is controlled by the chemical reaction.

Palladium and its alloys have been extensively studied because of their faculty to store reversibly hydrogen isotopes. Here, the substitution of palladium with platinum is investigated. Thermodynamical studies have shown an anomalous behaviour regarding to the classical models. This original behaviour is explained by the study of the electronic structure of the binary solid solutions. The drastic decrease of the hydrogen solubility in the Pd–Pt alloys is accounted for by the filling up of the palladium conduction band by the valence electrons of platinum. The anomalous decrease of the stability of the hydride is explained by the large broadening of the valence band due to the substitution.

The study of the physicochemical characteristics of titanium thin films and the corresponding deuterium absorption/desorption kinetics was performed. In order to optimize the production of high-energy neutrons the behaviour of deuteride titanium targets has been studied experimentally by bombardment with 120 and 350kV deuterons by means of electrostatic accelerators. The importance of the deposit evaporation conditions on the efficiency of neutron emission is clearly demonstrated as well as the thermomechanical stability of the Ti thin film by deuteron bombardment. The main parameters involved in the targets behaviour have been discussed from a thermodynamical approach.

In-situ internal stress determinations by X-ray diffraction have been performed during pure iron oxidation (p(O2)=2×10−3 Pa, T=800°C). The compressive stress, initially present in a blank substrate, due to surface preparation, is completely released at 400°C. On yttrium implanted iron no stress is initially present in the substrate. Under oxidising conditions, the in-situ compressive stress level determined in the FeO scale during oxidation does not strongly depend on the presence of implanted yttrium. On blank and implanted specimens, the compressive stress changes from −400±80 to −150±100 MPa after 30 h oxidation. However, after cooling to room temperature, blank specimens show compressive residual stresses, while implanted samples show tensile residual stresses. Our results also indicate that epitaxial relationships between the oxide scale and the substrate can be a source of stress in an oxide scale. A way to lower compressive stresses can be the use of yttrium ion implantation.

This work presents the influence of CeO2 surface modification on the stress developed during pure iron oxidation (p(O-2) = 2x10(.3) Pa, T = 800 degrees C). On blank and coated specimens, the compressive stress varies from -400 +/- 80 MPa to -150 +/- 100 MPa during the 30 hours oxidation test. The in-situ XRD compressive stress level determined in the FeO scale is not strongly dependent upon the presence of a ceria coating under conditions where no strong epitaxial relationships exist between FeO and a blank specimen. Surface modification by low pressure starting conditions induce epitaxial relationships between the FeO scale and iron. This leads to a high in-situ compressive stress in the oxide scale. This indicates that epitaxial relationships can be a source of stress in an oxide scale. A way to lower compressive stress in the scale can be the use of a ceria coating, known to prevent epitaxial relationships.

In situ XRD stress determinations have been performed during oxidation of pure iron (p(O2=2 × 10−3 Pa,T=800°C)). The compressive stress, initially present in the substrate due to surface preparation, is completely released at 400°C. Under the test conditions, the in situ compressive-stress level determined in the FeO scale during oxidation is not strongly dependent upon the presence of a ceria coating. On blank and coated specimens, the compressive stress varies from −400 ± 80 MPa to −150 ± 100 MPa during 30 hr oxidation. The decrease is quicker at the beginning of the test performed on blank specimens. Epitaxial relationships between the wüstite scale and iron (under low-pressure starting conditions) caused thein situ compressive stress in the oxide scale to be two times greater compared to the usual test conditions. This indicates that epitaxial relationships can be a source of stress in an oxide scale that ceria coatings may lower compressive stresses.

Zirconium oxidation mechanism can be studied by X-ray diffraction methods : in fact, the interactions between chemical (oxide growth, phases proportion) and physical process (oxide scale texture, mechanical stresses) are observed The oxide formed is composed of two allotropic structures, monoclinic ZrO2 (highest proportion) and tetragonal ZrO2 (trace). XRD studies show :1) phases analyses: phases gradient are revealed by XRD variable incidence.2) textures: Spatial evolution of monoclinic zirconia texture through the oxide scale is shown, and quantified3) mechanical stresses : several relaxations of the oxide compressive stresses occur at different times of the oxidation. They are correlated to kinetics breakaway, revealed by other methods.A structural mechanism of the oxide formation is then proposed, which prove the XRD interest in the heterogeneous kinetics researches.

This paper describes a device dedicated to studying, by X-ray diffraction the residual stresses developed on surface samples as a function of temperature and atmosphere conditions.The setup consists of:a.) an horizontal axis goniometer which allows the programmed positionning of the sealed X-ray source and of the linear detector.b.) a high temperature controlled atmosphere chamber. Particular attention has been paid to the thermal stability up to 1200 degrees C and the accurate position on the sample.

Uranium metal and U-0.2wt.%V alloy are very sensitive to hydrogen contamination. Prevention of hydride formation, a basic problem, can be approached by modifying the surface characteristics. Implantations of oxygen, nitrogen, carbon and sulphur ions have been tested as a function of dose from 2 × 1016 to 2 × 1018 ions cm−2. The main results are an increase in the induction time, which is multiplied by factors of 20–80 depending on the implanted species, and a change in the nucleation and growth mechanism from instantaneous nucleation (3 × 105 nuclei cm−2, 125 °C, PH2 = 5 kPa) to a pitting attack (from 300 to less than 10 pits cm−2) according to the species. Characteristics of the implanted shells have been determined by secondary ion mass spectrometry and X-ray diffraction.

Samples of LaNi5H6 were synthesized in a high-pressure thermobalance, several sample containers were used, differing in shape, lateral surface and thermal conductivity. Comparative studies were made using thermal analysis. Experimental results show that a large lateral surface of the sample holder improves the heat transfer. In the case of the other holders, the temperature variations are important and experiments cannot be carried under isothermal conditions.

Modelling studies are of practical importance in understanding and characterizing the kinetic behaviour of LaNi5 hydride. Theoretical predictions describing the reaction kinetics under non-isothermal conditions are in good agreement with the experimental data obtained in our experiments.

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