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International audience; Tungsten heavy alloys (Co-Ni-W) of different compositions were prepared by powder metallurgy (solid sintering), heat treated at 800°C and 1000°C and subsequently analyzed. The experimental phase identifications and composition measurements emphasized discrepancies compared to the isothermal ternary sections simulated with commercial thermodynamic databases. The isothermal sections at 800°C and 1000°C were found more complex than expected since a new intermetallic phase appeared to be stable (D0a structure-Cu3Ti prototype). Likewise, an interpretation of phase equilibria evolution with temperature was established to reach agreement with high temperature data. Formation enthalpies associated with the new phase were obtained through first-principles calculations and supported experimental results as they confirmed the stabilizing role of Ni addition for the D0a structure.

Accelerator magnets that can reach magnetic fields well beyond the Nb-Ti performance limits are presently being built and developed, using Nb3Sn superconductors. This technology requires reaction heat treatment (RHT) of the magnet coils, during which Nb3Sn is formed from its ductile precursor materials (a “wind and react” approach). The Nb3Sn microstructure and microchemistry are strongly influenced by the conductor fabrication route, and by the phase changes during RHT. By combining in situ differential scanning calorimetry, high energy synchrotron x-ray diffraction, and micro-tomography experiments, we have acquired a unique data set that describes in great detail the phase and microstructure changes that take place during the processing of restacked rod process (RRP), powder-in-tube (PIT), and internal tin (IT) Nb3Sn wires. At temperatures below 450 °C the phase evolutions in the three wire types are similar, with respectively solid state interdiffusion of Cu and Sn, Cu6Sn5 formation, and Cu6Sn5 peritectic transformation. Distinct differences in phase evolutions in the wires are found when temperatures exceed 450 °C. The volume changes of the conductor during RHT are a difficulty in the production of Nb3Sn accelerator magnets. We compare the wire diameter changes measured in situ by dilatometry with the phase and void volume evolution of the three types of Nb3Sn wire. Unlike the Nb3Sn wire length changes, the wire diameter evolution is characteristic for each Nb3Sn wire type. The strongest volume increase, of about 5%, is observed in the RRP wire, where the main diameter increase occurs above 600 °C upon Nb3Sn formation.

T2-Al2MgC2 was synthesized from the elements in a Mg-Al melt at 1000 °C using sealed Ta crucibles. Single crystals of T2-Al2MgC2 were extracted by evaporating the Mg-Al matrix. The crystal structure of T2-Al2MgC2 was refined for the first time on the basis of single-crystal X-ray diffraction. The crystal is trigonal (space group P-3m1, Z = 1) with lattice parameters of a = 3.3767(11) A, c = 5.807(2) A and V = 57.34(5) A3. Based on the refined crystal structure, DFT calculations were conducted to evaluate the thermodynamic properties and the electronic structure of the phase. The heat of formation of T2-Al2MgC2 was calculated to be −23.6 kJ/mol of atoms at 298 K. The heat capacity of T2-Al2MgC2 was measured by DSC from 300 to 871 K and calculated by DFT from 0 to 1000 K. Based on the calculated heat capacity, the entropy of formation of the phase at 298 K was determined to be 70.0 J/mol/K. The band structure and the electronic density of state of T2-Al2MgC2 was calculated leading to an indirect band gap value of 1.73 eV.

International audience; The Al–C system is the backbone of wide variety of applications in multicomponent systems, and was therefore studied intensively. Yet, considerable disagreements remain in the reported data, and the phase equilibria in the binary system as well as the standard enthalpy of formation of Al4C3 are still debated. In order to establish a reliable thermodynamic description of the Al–C system a thorough and critical assessment of the literature was conducted. The data on the solubility of carbon in liquid Al and on the thermodynamic properties of Al4C3 were assessed, and the peritectic decomposition temperature of Al4C3 was confirmed at 2425 ± 15 K by thermal analysis. Thermodynamic modeling of the Al–C system is provided and compared to previous works. The proposed description was found to be more robust and to carry more physical meaning than any previous modeling of the system, which imply an easier extrapolation of the binary into higher-order systems.

We investigate the formation and dissolution of hydrides in commercially pure zirconium powder in-situ using high-energy synchrotron X-ray radiation. Experimental results showed a continuous phase transition between the δ and e zirconium hydride phases with indication of a second order phase transformation.

We have studied the influence of the oxygen partial pressure $\text{pO}_{2}$ up to 5.5 bar on the phase changes that occur during the melt processing of a state-of-the-art Bi-2212 multifilamentary wire. Phase changes have been monitored in situ by high energy synchrotron X-ray diffraction. We found that the stability of the Bi-2212 phase is reduced with increasing $\text{pO}_{2}$ . For $\text{pO}_{2} > 1\ \text{bar}$ , a significant amount of the Bi-2212 phase decomposes upon heating in the range of 400 °C–650 °C. The extent of decomposition strongly increases with increasing pO2, and at $\text{pO}_{2}=5.5\ \text{bar}$ Bi-2212 completely decomposes in the solid state. Textured Bi-2212 can be formed during solidification when pO2 is reduced to 0.45 bar when the precursor is molten. Since the formation of current-limiting second phases is very sensitive to pO2 when it exceeds 1 bar, we recommend to reduce the oxygen partial pressure below the commonly used $\text{pO}_{2}=1\ \text{bar}$ , in order to increase the pO2 margins and to make the overpressure process more robust.

Alloying of vanadium with a combination of titanium and chromium has been investigated in this study. Hydrogenation/desorption of several alloys under similar experimental conditions has been performed and sequentially followed by means of in situ X-Ray powder diffraction. This latter technique has been used as a probe of formation or decomposition of hydrides. Geometrical effects are discussed and account for the observed similarities of the sorption properties.

International audience; In the scope of supporting the development of Mg–Al alloys and related materials, an experimental study coupled with a CALPHAD thermodynamic modeling of the Al–C–Mg system was conducted. The peritectic decomposition of Al2MgC2 to form Al4C3, graphite and a liquid phase was measured at 1559 ± 10 K by DTA. In order to model the Mg solubility in Al4C3, DFT calculations were performed on the end-member phases Mg4C3, Al2Mg2C3 and Mg2Al2C3 and it was shown that Mg substitutes on the Al2 crystallographic site of the carbide structure. Based on recent literature data and a revised Al–C binary, a model description of the Al–C–Mg ternary is proposed for the first time. More specifically, it is used to calculate the liquidus projection and the phase formation sequence during Scheil solidification of a 91Mg–9Al wt% alloy inoculated with carbon. This work provides a convincing argument that Al2MgC2 is the nucleant responsible for the grain refinement of Mg–Al alloys inoculated by C.

The reaction tending toward thermodynamic equilibrium during the synthesis of Ti/TiC MMC prepared by the powder metallurgy route was studied by in situ synchrotron X-ray diffraction. The carbide composition was found to change rapidly from its initial stoichiometric value TiC0.96 toward a substoichiometric value (TiC0.57) corresponding to thermodynamic equilibrium with the C-saturated Ti matrix. The reaction rate is very fast, and the solid-state reaction is almost complete after only a few minutes at 1073 K (800 °C) for the smallest particles, whereas the rate-limiting step remains the particle size. In addition, modeling of the diffusion processes in MMCs, i.e., initial dissolution of particles and their trend toward equilibrium composition, was performed using three particles size classes and the calculations were performed using the ThermoCalc and Dictra package. First, dissolution of the smallest particles (10% of the initial TiC0.96 particles) is expected to be achieved after only 1 s at 800 °C. Second, the change in TiC composition leads to an increase in the total amount of carbide in the composite from 16 to 19 mass%. The consequences on the industrial process of Ti/TiC MMC synthesis have also been considered. A typical industrial heat treatment of a MMC billet, 1 h at 900 °C, was modeled, and the results showing an increase in the total amount of carbide in the composite from 16 to 22 mass% are in rather good agreement with the experimental value (21 mass%). This highlights the potential of thermodynamic and kinetic modeling to help understand and optimize industrial processes for MMC synthesis.

Grain refinement of Mg–Al based alloys is challenging because it is known that Zr, which is extremely effective in many Al-free alloys, cannot be used. The addition of carbon through various routes by using carbon-containing sources is considered as an option. The grain refinement mechanisms are still under debate. The present work is focused on the ternary base system Mg–Al–C, including the potential nucleants Al4C3 and Al2MgC2, presently without consideration of Al2CO. The ternary carbide Al2MgC2 was synthesized and characterized using sealed Ta crucibles. The decomposition of the carbide was measured at 1290 °C by Differential Thermal Analysis under a pressure of 8 bar. Practical difficulties, including high vapor pressure of Mg and high affinity of Mg with oxygen, as well as rapid hydrolysis of the Al2MgC2 carbide have been overcome.

A metal matrix composite has been obtained by a novel synthesis route, reacting Al 3 Ti and graphite at 1000 °C for about 1 min after ball-milling and compaction. The resulting composite is made of an aluminium matrix reinforced by nanometer sized TiC particles (average diameter 70 nm). The average TiC/Al ratio is 34.6 wt.% (22.3 vol.%). The microstructure consists of an intimate mixture of two domains, an unreinforced domain made of the Al solid solution with a low TiC reinforcement content, and a reinforced domain. This composite exhibits uncommon mechanical properties with regard to previous micrometer sized Al–TiC composites and to its high reinforcement volume fraction, with a Young’s modulus of ∼110 GPa, an ultimate tensile strength of about 500 MPa and a maximum elongation of 6%.

The evolution of TiC reinforcement during the high-temperature consolidation step of a particulate-reinforced Ti matrix composite has been studied. A four-step scenario has been highlighted starting with the dissolution of the smallest particles to reach C saturation of the Ti matrix, followed by a change in the TiC stoichiometry from the initial TiC0.96 composition to the equilibrium composition (TiC0.57). This change in composition induces an increase in both the total mass fraction of reinforcement and the particle diameter. The diameter increase promotes contact between individual particles in the most reinforced domains and initiates an aggregation phenomenon that is responsible for the observed high growth rate of particles for heat treatment times shorter than 1 h. Finally Ostwald ripening is responsible for the growth of particles for longer heat treatment times.

We report an in operando study of the hydrogenation and dehydrogenation of MgH 2 –TiVCr composites. The experiment was performed by means of in situ synchrotron XRD in order to get insights on the influence of the TiVCr additive on the sorption properties of the MgH 2 based composite. Sequential Rietveld refinement analysis was performed to investigate the structural changes of MgH 2 and of the additive during hydrogenation and dehydrogenation processes. Significant non-monotonic changes in the lattice volume of the TiVCrH x solid solution were observed concomitantly to the MgH 2 formation or decomposition. These volume changes are assigned to the variation of the hydrogen content in TiVCrH x . These results provide evidence of cooperative effects between the H 2 storage material and the additive.

© 2013 International Union of Crystallography, Different solutions have been proposed over the years to optimize control of the temperature and atmosphere over a catalyst in order to reach an ideal reactor behavior. Here, a new innovative solution which aims to minimize temperature gradients along the catalyst bed is demonstrated. This was attained by focusing the infrared radiation generated from the heating elements onto the catalyst bed with the aid of an aluminium shield. This method yields a ∼0.13Kmm-1 axial temperature gradient ranging from 960 to 1173K. With the selection of appropriate capillaries, pressures of 20bar (2MPa) can be attained., The research leading to these results has been funded by the Spanish CICYT (CTQ2010-14872/BQU) and the European Union's Seventh Framework Programme (FP7/2007–2013) under grant agreement No. 253445. KCC acknowledges Marie Curie Action – Intra-European Fellowship (FP7-PEOPLE-2009-IEF-253445) for a postdoctoral fellowship.

Synchrotron X-ray diffraction was used to evaluate strain evolution observed in Zircaloy-4 undergoing hydride precipitation during a range of thermal operations. During continuous heating, a change in the constraining effect of the matrix was observed at a temperature of 280 °C, thought to be the result of matrix dilatation from interstitial hydrogen. A deconvolution of the thermal, chemical and mechanical sources of strain during quench and dwell operations identified a non-negligible mechanical effect in the matrix. During these dwells, slow strain rate relaxation of elastic strains was seen in the matrix and hydride, suggesting that time dependent relaxation of misfit stresses may be possible at reactor relevant temperatures. Notable anisotropy was observed between the rolling and transverse directions, identified as being the likely product of a similar anisotropy in the relaxation of the hydride misfit between the 11 2 ¯ 0 > α and 1 1 ¯ 00 > α matrix directions, owing to the differing coherency of these two interfaces.

International audience; The present study focused on kinetics of hydrogen release through hydrolysis of sodium borohydride NaBH4 in the presence of cobalt nanoparticles. Our experimental conditions were quite severe as we worked over the widest temperature range ever reported (i.e. 10–90 °C) and at high content of hydride (mol ratio NaBH4/water of 9; i.e. 18.9 wt% NaBH4 or 6.18 mol L−1). From the hydrogen evolution curves, the reaction constant versus the NaBH4 concentration, apparent activation energy, rate constant, adsorption constant and adsorption enthalpy were determined. It was noticed that the hydrolysis kinetics depends on (i) temperature of reaction and (ii) NaBH4 concentration. Hence, the kinetic constants were analyzed using existing kinetic models. The bimolecular Langmuir–Hinshelwood model satisfactorily captured the behavior of our catalyst consisting of cobalt nanoparticles (in our experimental conditions). Herein, the kinetic data, the kinetic model, the hydrolysis mechanism and the issues still to be addressed are reported and discussed.

International audience; Today there is a consensus regarding the potential of NaBH4 as a good candidate for hydrogen storage and release via hydrolysis reaction, especially for mobile, portable and niche applications. However as gone through in the present paper two mains issues, which are the most investigated throughout the open literature, still avoid NaBH4 to be competitive. The first one is water handling. The second one is the catalytic material used to accelerate the hydrolysis reaction. Both issues are object of great attentions as that can be noticed throughout the open literature. This review presents and discusses the various strategies which were considered until now by many studies to manage water and to improve catalysts performances (reactivity and durability). Published studies show real improvements and much more efforts might lead to significant overhangs. Nevertheless the results show that we are still far from envisaging short-term commercialization.

The preparation of a new trisodium triborate, Na(3)[B(3)O(4)(OH)(4)], and its complete characterization in terms of molecular structure and thermal behavior are reported. Synthesis of this compound was achieved either by NaBH(4) hydrolysis or by thermal treatment of Na[B(OH)(4)].2H(2)O. The crystal structure was determined by single-crystal X-ray diffraction. The trisodium triborate crystallized in the monoclinic system (a = 12.8274(6) A, b = 7.7276(4) A, c = 6.9690(3) A, and beta = 98.161(3) degrees ), space group Cc, Z = 2. The structure of Na(3)[B(3)O(4)(OH)(4)] comprised [B(3)O(4)(OH)(4)](3-) polyanions, based on B-O-containing rings with two tetracoordinated boron atoms and one tricoordinated boron atom in the fragments BO(2)(OH)(2) and BO(3), respectively. These polyanions are interconnected by four intermolecular hydrogen bonds and presented a tilt of 10.470(4) degrees compared to the a axis. Thus, they are stacked by rotation of about 180 degrees around an axis defined by the three-coordinated boron atoms and parallel to the c axis. Such polyanions were only observed previously in two synthetic compounds, M(3)[B(3)O(4)(OH)(4)].2H(2)O with M = K and Rb, which were isostructural. The originality of the present work was the synthesis and the description of a different crystallographic structure containing this polyanion. Characteristic peaks ranging from 500 to 1500 cm(-1) and around 3300 cm(-1) highlighted the presence of the B-O rings and hydroxyl groups, respectively. The decomposition temperature T = 155 degrees C was obtained by thermogravimetric analysis, and the following equivalent formula in terms of hydration degree was proposed: NaBO(2).(2)/(3)H(2)O. Na(3)[B(3)O(4)(OH)(4)] decomposed into Na(3)[B(3)O(5)(OH)(2)] in equilibrium with its vapor.

International audience; In the present work, hydrogen generation through hydrolysis of a NaBH4(s)/catalyst(s) solid mixture was realized for the first time as a solid/liquid compact hydrogen storage system using Co nanoparticles as a model catalyst. The performance of the system was analysed from both the thermodynamic and kinetic points of view and compared with the classical catalyzed hydrolysis of a NaBH4 solution. The kinetic analysis of the NaBH4(s)/catalyst(s)/H2O(l) system shows that the reaction is first order with respect to the catalyst concentration, and the activation energy equal to 35 kJ molNaBH4−1. Additionally, calorimetric measurements of the heat evolved during the hydrolysis of NaBH4 solutions evidence the global process energy (−217 kJ molNaBH4−1). Characterization of the cobalt nanoparticles before and after the hydrolysis associated with the calorimetric measurements suggests the “in situ” formation of a catalytically active CoxB phase through “reduction” of an outer protective oxide layer that is regenerated at the end of reaction.

Chemical interaction of Ti3SiC2 substrate with silver–copper (Ag–Cu) melt is studied after several minutes of contact at 800 °C and 900 °C. Experimental evidence of Cu insertion into the crystallographic structure of Ti3SiC2 is given both by X-ray energy dispersive spectroscopy (composition is about Ti47Cu8Si13C32) and by electronic diffraction patterns obtained by transmission electronic microscopy for single grains. Moreover, the X-ray diffraction pattern shows that insertion of Cu induces a slight increase in the lattice parameters and a modification of peak intensities.

Commercial-grade Zr powder loaded with hydrogen in situ and phase transformations between various Zr and ZrHx phases have been monitored in real time., For the first time, various hydride phases in a zirconium–hydrogen system have been prepared in a high-energy synchrotron X-ray radiation beamline and their transformation behaviour has been studied in situ. First, the formation and dissolution of hydrides in commercially pure zirconium powder were monitored in real time during hydrogenation and dehydrogenation, then whole pattern crystal structure analysis such as Rietveld and Pawley refinements were performed. All commonly reported low-pressure phases presented in the Zr–H phase diagram are obtained from a single experimental arrangement.

Polarization reversal in polycrystalline ferroelectrics is shown to occur via two distinct and sequential domain reorientation steps. This reorientation sequence, which cannot be readily discriminated in the overall sample polarization, is made apparent using time-resolved high-energy x-ray diffraction. Upon application of electric fields opposite to the initial poling direction, two unique and significantly different time constants are observed. The first (faster time constant) is shown to be derived by the release of a residual stress due to initial electrical biasing and the second (slower time constant) due to the redevelopment of residual stress during further domain wall motion. A modified domain reorientation model is given that accurately describes the domain volume fraction evolution during the reversal process.

The nature of liquid-solid phase equilibria in the Al-rich corner of the Al-Si-Ti system are determined by drawing three isothermal sections at 620, 680 and 727 °C. The solubility of Ti in Al-Si liquids is determined for four different compositions (0, 9, 13 and 18 at.%Si) at temperature below 800 °C. Combination of the two sets of experimental results leads to an attempt of liquidus projection. The primary crystallization surface of Al3Ti is found to extend up to 9.5 at.%Si in the liquid phase at 620 °C and 11 at.%Si at 727 °C. The solubility of Ti is found to be not significantly dependent on the Si content of the liquid. From DSC measurements and deduction on microstructure, the last invariant reaction of the solidification path is found to be quasi-peritectic: $${\text{L}} + \uptau_{1} - {\text{Ti}}_{7} {\text{Al}}_{5} {\text{Si}}_{12} \Leftrightarrow {\text{Al}} + {\text{Si}} .$$

International audience; The solubility of group IV transition metals Ti, Zr, and Hf in liquid Al was measured by the settling technique coupled with ICP-AES analysis after dissolution in hydrochloric acid. The kinetic aspect of the settling technique was studied in order to show that, after a cooling step, thermodynamic equilibrium between the liquid and solid phases could be achieved after only 1 h. Finally, it was verified that solubility values obtained after a cooling or a heating step were fully consistent. The present results demonstrate that the immersion-and-settling technique allows reliable solubility values to be determined. The results confirm the values previously reported in the literature and the good description for the three binaries by the existing CALPHAD optimizations concerning the liquidus below 800 C.

A high-pressure–high-temperature gas-loading system (GLS) is described for combinedoperandoX-ray diffraction and mass spectrometry investigations during catalysed gas/solid or liquid/solid reactions. The pressure cell consists of a single-crystal sapphire tube which serves as both high-pressure container and reaction cell, with up to 6 mm inner diameter. The system can operate in two different configurations, under either static high pressure or dynamic pressurized flow. The transportable reaction cell can be filled under inert atmosphere inside a glove box, enabling studies with oxygen-sensitive compounds to be conducted. The five main benefits of this system can be summarized as follows: (i) the temperature, pressure and gas-flow ranges of 298–1273 K, 10−3 mbar–200 bar (0.1–2 × 107 Pa) and 0–1 l min−1, respectively, (ii) the combination of different gases, (iii) the flexibility of the cell design, (iv) the full rotation of the pressurized cell, and (v) the combination of X-ray diffraction and mass spectrometry as analytical tools. These key points open new possibilities for studying the evolution of catalysts or compounds from a fundamental point of view as well as for industrial applications, in both cases inoperandoconditions.

International audience; The formation of ultra-small Mg-based particles nanoconfined into the mesopores of a carbon template was studied by in situ synchrotron diffraction. Either Mg2Ni or Mg2NiH4 nanoparticles can be directly formed starting from separate Ni and MgH2 nano-species by tuning the H2 pressure and temperature. Both ultra-small Mg2Ni and Mg2NiH4 nanoparticles (∼4 nm) are extremely stable against coalescence during hydrogen sorption cycling and prolonged exposure to high temperature as compared to Mg and MgH2 nanoparticles that show severe coalescence under same experimental conditions. The structural transition reported in bulk Mg2NiH4 from high temperature cubic to low temperature monoclinic structure is no longer observed for the nanoconfined particles. Hydrogen absorption/desorption in nanosized Mg2Ni is reversible and sorption kinetics proceed very quickly (∼5 min) even at 483 K. On the contrary, the thermodynamics properties are not altered by nanoconfinement. This study opens new routes for successful nanoconfinement of stoichiometric hydrides into the pores of carbon hosts along with a better understanding of the underlying nanochemistry.

The binary phase diagram NaBO2–H2O at ambient pressure, which defines the different phase equilibria that could be formed between borates, end-products of NaBH4 hydrolysis, has been reviewed. Five different solid borates phases have been identified: NaBO2·4H2O (Na[B(OH)4]·2H2O), NaBO2·2H2O (Na[B(OH)4]), NaBO2·2/3H2O (Na3[B3O4(OH)4]), NaBO2·1/3H2O (Na3[B3O5(OH)2]) and NaBO2 (Na3[B3O6]), and their thermal stabilities have been studied. The boundaries of the different Liquid + Solid equilibria for the temperature range from −10 to 80 °C have been determined, confirming literature data at low temperature (20–50 °C). Moreover the following eutectic transformation, Liq. → Ice + NaBO2·4H2O, occurring at −7 °C, has been determined by DSC. The Liquid–Vapour domain has been studied by ebullioscopy. The invariant transformation Liq. → Vap. + NaBO2·2/3H2O has been estimated at 131.6 °C. This knowledge is paramount in the field of hydrogen storage through NaBH4 hydrolysis, in which borate compounds were obtained as hydrolysis reaction products. As a consequence, the authors propose a comparison with previous NaBO2–H2O binary phase diagrams and its consequence related to hydrogen storage through NaBH4 hydrolysis.

The hydrogen sorption properties of LaCuMg 8 are investigated. LaCuMg 8 crystallizes in the La 2 Mg 17 structure type with the lattice parameters a = 10.1254(2) A and c = 10.0751(2) A. An absorption mechanism in 2 steps was reported earlier: (i) the first step, which is irreversible, induces the decomposition of LaCuMg 8 into an intimate mixture of 3 phases of sub-micronic size ( i.e. LaH 3 , MgCu 2 and MgH 2 ); (ii) the second step consists in the reversible absorption of the “LaCuMg 8 activated powder” with kinetics better than for pure magnesium. In order to get a better understanding of the absorption process, it was investigated from thermodynamic, kinetic and morphology points of view. From thermodynamic point of view, the “LaCuMg 8 activated powder” behaves like a mixture. Concerning the kinetics, the activation energy was evaluated at about 65 kJ/mol H 2, using Avrami–Erofeev model and Arrhenius law. To explain the enhancement of the kinetics, both effects of (i) Mg 2 Cu/MgCu 2 transformation and (ii) morphology induced by the decomposition have been considered.

Non-destructive, quantitative and precise determination of internal strain distributions within structural materials and components can be accomplished by only a few experimental techniques, amongst which diffraction of penetrating radiation (X-ray and neutron beams) plays a central role. However, due to the various limitations of these methods, the 2-D and 3-D mapping of internal strains within bulk cross-sections at a spatial resolution of 0.1 mm or better has long remained a challenge. The principle of "strain tomography" proposed by the present authors (an instance of broader "rich" tomography methodology) makes use of the reconstruction tomography technique widely employed in imaging applications. In the present paper we report successful practical implementation of this principle to the study of bending strains in sintered polycrystalline zirconia used in the fabrication of multi-unit fixed prosthetic dentures. The results demonstrate the power of the technique, and pave the way to wider application of this approach to cross-sectional strain mapping in complex-shaped components under various loading conditions. © 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

The present study reports fundamental results about the spontaneous hydrolysis of sodium borohydride NaBH4, which is a potential hydrogen storage material for small, portable applications. The reaction (without stabilizing agent or catalyst) was carried out at temperatures of 30–80 °C, initial NaBH4 concentrations of 0.63–6.19 mol L−1 (2.3–18.9 wt%), and for unbuffered solutions, which are harsher experimental conditions than those reported so far. The H2 evolution and the subsequent pH variation were observed to determine the reaction kinetic parameters and characterize the hydrolysis intermediates, i.e. the hydroxyborates BH4−z(OH)z−, by XRD, IR and 11B NMR. It was found that: (i) the apparent activation energy of the reaction was 98 ± 10 kJ mol−1 and the reaction order versus the initial NaBH4 concentration was 0; (ii) all of the reactions BH4− → BH3(OH)−, BH3(OH)− → BH2(OH)2−, BH2(OH)2− → BH(OH)3− and BH(OH)3− → B(OH)4− took place simultaneously; (iii) only 25 mol% of B(OH)4− and 75 mol% of BH4− were found at 25% of conversion; (iii) the hydroxyborates are very short-lived intermediates and only traces of BH3(OH)− were detected.

Potassium borohydride KBH4 is an attractive chemical hydride for H2 generation and storage in portable fuel cell applications. Nevertheless, the control of the by-products, in terms of stability and solubility in aqueous solutions, is one of the limiting steps of the hydrolysis reaction of H2 release. We report here some physicochemical properties of concentrated KBO2 aqueous solutions: solubility and gravimetric density are measured as function of temperature between 10 to 80°C. The stability of hydrated metaborates KBO2.xH2O solid phases (with x = 4/3 and 4) in alkaline aqueous solutions is also evaluated at 20°C.

International audience; Reaction zones formed at 790 °C between solid titanium and liquid Ag-Cu eutectic alloys (pure and Ti-saturated) have been characterized. When pure Ag-Cu eutectic alloy with 40 at.% Cu is used, the interface reaction layer sequence is: alpha-Ti / Ti2Cu / TiCu / Ti3Cu4 / TiCu4 / L. Because of the fast dissolution rate of Ti in the alloy, the reaction zone remains very thin (3-6 µm) whatever the reaction time. When the Ag-Cu eutectic alloy is saturated in titanium, dissolution no longer proceeds and a thicker reaction zone with a more complex layer sequence grows as the reaction time increases. Four elementary chemical interaction processes have been identified in addition to Ti dissolution in the liquid alloy. These are growth of reaction layers on Ti by solid state diffusion, nucleation and growth from the liquid of TiCu4, isothermal solidification of silver and, finally, chemical conversion of the Cu-Ti compounds by reaction-diffusion in the solid state. A mechanism combining these processes is proposed to account for the constitution of Ti/ Ag-Cu/ Ti joints brazed at 780-800 °C.

International audience; Titanium has been successfully joined to aluminium nitride AlN at a temperature as low as 795 ◦C, using Ag–Cu Cusil® commercial braze alloy. While reactive wetting and spreading proceeds at the AlN/braze alloy interface, chemical interactions develop at the titanium side rendering possible isothermal solidification of the joint. The determining factor in the solidification process is the fast formation of TiCu4 crystals by heterogeneous nucleation and growth in the liquid phase. As a consequence, the braze alloy is depleted in Cu and solid Ag precipitates. After annealing, the re-melting temperature of the resulting joint can be increased up to about 910 ◦C which is nearly 130 ◦C higher than the melting point of the starting braze alloy.

International audience; This paper presents observations of in situ heating and cooling cycles using synchrotron X-ray diffraction carried out on Zircaloy-4 plates charged to different levels of hydrogen content. The diffraction peak intensities were used to derive the weight fraction of hydrogen in solid solution and the solvi curves upon dissolution and precipitation. The heating and cooling rate did not seem to have a major influence on the solvi. Fast-cooling/dwell experiments showed that the precipitation kinetics are very fast. Finally the evolutions of the lattice strains from individual grain families were studied during dissolution and precipitation. The aim was to understand the role of interphase misfit stresses on the mechanisms of hydride formation and hysteresis between dissolution and precipitation. The results emphasise that changes in dissolved H concentration are responsible for a non-negligible part of the lattice distortion in the matrix, and that the diffraction strains must therefore be analysed with care.Highlights► Dissolution and precipitation of Zr hydrides followed in situ using X-ray synchrotron diffraction. ► Fast kinetics of precipitation at 400 °C. ► Little contribution of heating/cooling rates to the hysteresis. ► Significant expansion of the hcp lattice in the matrix by the addition of interstitial hydrogen atoms during dissolution.