An optical study of alumina films thermal evolution upon ammonia annealing

The physical and structural evolution of alumina films deposited by ALCVD annealed at high temperatures in N₂ has been studied.Low temperature post deposition treatments in NH₃ (PDN) have been performed to evaluate the impact of nitrogen incorporation in the alumina film on its thermal stability. Thermal evolution has been studied by deep UV spectroscopic ellipsometry and grazing X-ray reflectance techniques. AFM measurements were also performed to confirm and complete the ellipsometric and GXR analysis.The change of the crystalline structure was detected by ellipsometry by the different UV refractive index, while the GXR provided a unique thickness evaluation.It was therefore possible to determine the layer densification after the thermal treatment and the impact of the PDN on the transition temperature.     

Nanoconfined LiBH4 as a Fast Lithium Ion Conductor

Designing new functional materials is crucial for the development of efficient energy storage and conversion devices such as all solid‐state batteries. LiBH₄ is a promising solid electrolyte for Li‐ion batteries. It displays high lithium mobility, although only above 110 °C at which a transition to a high temperature hexagonal structure occurs. Herein, it is shown that confining LiBH₄ in the pores of ordered mesoporous silica scaffolds leads to high Li⁺ conductivity (0.1 mS cm^?1) at room temperature. This is a surprisingly high value, especially given that the nanocomposites comprise 42 vol% of SiO₂. Solid state ⁷Li NMR confirmed that the high conductivity can be attributed to a very high Li⁺ mobility in the solid phase at room temperature. Confinement of LiBH₄ in the pores leads also to a lower solid‐solid phase transition temperature than for bulk LiBH₄. However, the high ionic mobility is associated with a fraction of the confined borohydride that shows no phase transition, and most likely located close to the interface with the SiO₂ pore walls. These results point to a new strategy to design low‐temperature ion conducting solids for application in all solid‐state lithium ion batteries, which could enable safe use of Li‐metal anodes.     

Interlaminar crack onset in co‐cured and co‐bonded composite joints under mode I cyclic loading

Composite joints exhibit different behavior in regard to delamination resistance when dealing with fatigue phenomenon. This research work focuses on an investigation to understand the failure mechanisms on the interfacial strength domain for delamination onset in cocured and cobonded joints. The analysis was based on strain energy release rate versus number of cycles plots that were obtained from fatigue tests in mode I with a stress ratio R = 0.1. The analysis encompassed from the microscopic to mesoscopic level obtained from scanning electron microscopic, and the images processed to extract the most relevant fracture patterns. The main difference between the two technologies was the stress concentration at the crack tip in which the cobonded joint presents a fabric carrier that blunts the adhesive layer, then delaying the delamination. This paper provides important information and guidelines to aid designers in the selection of the best composite joint for high‐performance structural applications.     

On the decomposition of the 0.6LiBH4-0.4Mg(BH4)2 eutectic mixture for hydrogen storage

The dehydrogenation reaction of the 0.6LiBH₄-0.4Mg(BH₄)₂ eutectic system was investigated by Temperature-Programmed-Desorption and Pressure-Composition-Isotherm methods, in the range of 25–540 °C and 0.1–150 bar of p(H₂). A sequence of four decomposition steps was found by TPD measurements; they occur at 235, 315, 365 and 460 °C for p(H₂) = 3 bar, with a clear T decrease with respect to pure LiBH₄ and Mg(BH₄)₂. In the PCI experiments, the first two steps could not be resolved but appeared merged in a single process. The amounts of H₂ release at each step and the Δ_rH and Δ_rS values derived from van’t Hoff plots were analyzed and compared with known results for relevant possible reactions. A scheme of interpretation was then proposed for all four processes. In particular, a fraction of LiBH₄ and Mg(BH₄)₂ would react together in the range of 300–350 °C according to 2LiBH₄ + Mg(BH₄)₂ → 2B + 2LiH + MgB₂ + 7H₂, thus explaining the quite large H₂ yield therein observed. The first and fourth steps correspond to decompositions of pure remaining Mg(BH₄)₂ and LiBH₄, respectively, and the third one to dehydrogenation of MgH₂ produced in the first step.