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Hydride formation in zircaloy-4 under cyclic thermomechanical loading has been investigated using characterized notched beam samples in four-point beam testing, and microstructurally-representative crystal plasticity modelling of the beam tests which incorporates an atomistically-informed thermodynamically-equilibrium model for hydrogen concentration. The model provided the locations within the microstructure of high hydrogen content, above that required for saturation, hence predicting the anticipated locations of hydride observations in the experiments. The strain rate sensitivity of this alloy over the temperature range considered led to considerable intragranular slip and corresponding stress redistribution, and cyclic strain ratcheting leading to high hydrostatic stresses and in turn hydrogen concentrations, which explains the locations of experimentally observed hydride formation. The interstitial hydrogen interaction energy as well as the intragranular geometrically necessary dislocation density were shown to be important in controlling the spatial distributions of observed hydrides.

Available experimental studies on the effect of the interfacial transition zone (ITZ) on transport properties of cement-based composite materials appear to be ambiguous. The main objective of this work was to enhance the understanding of the relationship between ITZ and transport properties of Portland cement-based materials by using both a rapid chloride migration test and theoretical calculations. A densification factor which is related to aggregate volume content was introduced to further determine the transport properties of ITZ. Results indicate that the overall porosity decreased with increasing aggregate volume content due to the dilution effect by impermeable aggregates. The porosity was above the theoretical dilution line obtained from P0×(1-Vagg) for mortars with more than 20% of aggregate, which can be attributed to the presence of high porous ITZ. On the other hand, more porous ITZ was expected to be accompanied by a denser bulk cement matrix, which leaded to a decrease in the porosity of mortar with less than 35% of aggregate. The ITZ effect would dominate the blocking aggregate, densification and tortuosity of bulk paste when aggregate volume content exceeded 0.35. The ratio between the migration coefficient of the ITZ and that of the matrix (DITZ/Dmatrix) increased with aggregate volume content and assumed ITZ thickness. In addition, the influence of ITZ increased with increasing the degree of interconnection slightly until 1.0. Beyond this value, a sudden increase in DITZ/Dmatrix ratio was observed indicating the negative percolation effect when the adjacent ITZ start to interconnect.

International audience; Cobalt-free AB5-type hydrogen storage alloys have been examined for the purpose of lowering metal hydride raw material costs. For this purpose, the electrochemical behaviour of cobalt-free LaNi3.55Mn0.4Al0.3Fe0.75 alloy was investigated using chronopotentiometry and electrochemical impedance spectroscopy. It was shown that the discharge capacity decreases by 50% after fifty cycles. To investigate the capacity decrease, the impedance measurements were conducted during charging at different stages of life cycle. The experimental impedance spectroscopy reveals that the metal hydride electrode exhibits a porous behaviour. The results were then analyzed on the basis of equivalent circuit model involving the porous electrode behaviour according to de Levie's model, i.e. equivalent cylindrical pores connected in parallel. The pore texture of electrode material was then estimated namely by the pore number, mean values of cylinder radius and effective length. The loss of discharge capacity is due to that of the reactivity of the electrode material and not the collapsing of pore texture.

Novel carbon films with different graphene layer orientations are investigated as electrode materials for Li-ion batteries. It is demonstrated that engineering the crystallographic orientation with graphene layers oriented perpendicular to the surface substantially alters stress evolution during Li insertion. With this crystallographic orientation the intercalating/de-intercalating Li-ions also have direct access to the graphene interlayer spaces, resulting in higher capacity at faster electrochemical cycling, compared to carbon films with graphene layers parallel to the film surface. Electrodes with perpendicular alignment are prepared by supramolecular synthesis using either spin coating or bar coating of chromonic liquid crystal precursors into precursor organic films followed by in situ carbonization. These materials are compared with in situ stress measurements during lithiation/delithiation cycles, and the bar-coated films exhibit a highly anisotropic stress which is consistent with long-range alignment of the graphene layers. In contrast, the in-plane stresses in the spin-coated films are isotropic, which is consistent with the presence of randomly oriented domains (still with graphene layers oriented perpendicular to the surface). Overall, the use of thin film graphitic materials with controlled crystallographic orientations provides a valuable platform for investigating the impact of graphene structure on the properties of Li-ion battery electrode materials.