Mechanical Properties and Microstructure of Binary In-Sn Alloys for Flexible Low Temperature Electronic Joints.

This research evaluates the mechanical properties of a variety of binary In-Sn alloys as potential candidates for low temperature electronic joints. The tensile and hardness tests of as-cast In-5Sn, In-12.5Sn, In-25Sn, In-30Sn, In-35Sn, In-40Sn, In-50Sn, In-60Sn, In-80Sn (wt.%) were assessed at room temperature and compared to those of pure In and Sn. The ultimate tensile strength (UTS) increased from 4.2 MPa to 37.8 MPa with increasing tin content in the alloys under the testing condition of 18 mm/min and the results showed little difference under a lower strain rate (1.8 mm/min). Most compositions showed good ductility in tensile testing with an average of 40% elongation. A melting point range of 119.3 °C to 194.9 °C for tested alloys was measured using differential scanning calorimetry (DSC). The microstructure investigated by scanning electron microscopy (SEM) was discussed with respect to the mechanical properties and it has been found that the presence of the Sn-rich γ-InSn4 phase in the microstructure has a significant impact on mechanical properties. The fundamental data from this study can be used for the development of new low temperature In-Sn alloys.

In Situ Observation of Liquid Solder Alloys and Solid Substrate Reactions Using High-Voltage Transmission Electron Microscopy.

The complex reaction between liquid solder alloys and solid substrates has been studied ex-situ in a few studies, utilizing creative setups to "freeze" the reactions at different stages during the reflow soldering process. However, full understanding of the dynamics of the process is difficult due to the lack of direct observation at micro- and nano-meter resolutions. In this study, high voltage transmission electron microscopy (HV-TEM) is employed to observe the morphological changes that occur in Cu6Sn5 between a Sn-3.0 wt%Ag-0.5 wt%Cu (SAC305) solder alloy and a Cu substrate in situ at temperatures above the solidus of the alloy. This enables the continuous surveillance of rapid grain boundary movements of Cu6Sn5 during soldering and increases the fundamental understanding of reaction mechanisms in solder solid/liquid interfaces.

Effect of Na and Cooling Rate on the Activation of Mg-Ni Alloys for Hydrogen Storage.

In spite of favourable hydrogen storage properties such as low density, high theoretical capacity (7.6 wt% H/MgH2) and economics, commercial use of Mg-based alloys is not feasible due to long activation times, slow hydrogen sorption kinetics, and a high temperature for hydrogen release. Mg- Ni alloys have been considered promising materials for hydrogen storage systems as the Mg2Ni intermetallic phase enhances the kinetics of hydrogen absorption in Mg-Ni alloys through a catalytic effect. It has been suggested that the refinement of eutectic in Mg-Ni alloys can further improve hydrogen absorption kinetics and that this can be achieved through trace Na additions. However, the refinement of the eutectic can also be achieved by increasing the cooling rate during solidification. In this study we investigate the effect of cooling rate and Na additions to Mg-Ni alloys on hydrogen absorption kinetics. Our results indicate that Na additions improve the hydrogen absorption kinetics independent of eutectic refinement and that the effect of the latter is relatively small.

The Effects of Trace Sb and Zn Additions on Cu6Sn5 Lithium-Ion Battery Anodes.

Sn-based compounds are promising candidates for application as anodes in lithium-ion batteries (LIBs) due to the favourable storage capacity of Sn at 993 mAh g-1 compared to carbon at 372 mAh g-1. The use of Sn-based anodes also avoids some of the safety concerns associated with carbon anodes. However, the large volume changes during lithiation and delithiation of pure Sn anodes often results in poor cyclic performance. Alloying Sn with Cu, an element inactive with respect to Li, buffers the expansion stresses and can improve cycling performance. Cu6Sn5 is therefore a promising candidate anode material. In this work, the effects of Sb and Zn additions on the morphology, crystal structure, atomic arrangements and the electrochemical performance of the anodes were evaluated. Characterisation with synchrotron X-ray powder diffraction and Cs-corrected transmission electron microscopy revealed the larger lattice parameters, higher symmetry crystal structures and well-ordered atomic arrangements in the Sb and Zn modified electrodes, which resulted in a more than 50% increase in cycling capacity from 490 mAh g-1 to 760 mAh g-1.

(Al,Mg)3La: a new phase in the Mg-Al-La system.

During an investigation of the Mg-rich end of the Mg-Al-La system, a new ternary phase with the composition of (Al,Mg)3La was identified. The crystal structure of this phase was determined by conventional X-ray powder diffraction and transmission electron microscopy analysis and refined using high-resolution X-ray powder diffraction. The (Al,Mg)3La phase is found to have an orthorhombic structure with a space group of C2221 and lattice parameters of a = 4.3365 (1) Å, b = 18.8674 (4) Šand c = 4.4242 (1) Å, which is distinctly different from the binary Al3La phase (P63/mmc). The resolved structure of the (Al,Mg)3La phase is further verified by high-angle annular dark-field scanning transmission electron microscopy.

Reply to 'Comments on "Evidence of the hydrogen release mechanism in bulk MgH2"'.

In a comment on our Article "Evidence of the hydrogen release mechanism in bulk MgH2", Surrey et al. assert that the MgH2 sample we studied was not MgH2 at any time but rather MgO; and that the transformation we observed was the formation of Kirkendall voids due to the outward diffusion of Mg. We address these issues in this reply.

Evidence of the hydrogen release mechanism in bulk MgH2.

Hydrogen has the potential to power much of the modern world with only water as a by-product, but storing hydrogen safely and efficiently in solid form such as magnesium hydride remains a major obstacle. A significant challenge has been the difficulty of proving the hydriding/dehydriding mechanisms and, therefore, the mechanisms have long been the subject of debate. Here we use in situ ultra-high voltage transmission electron microscopy (TEM) to directly verify the mechanisms of the hydride decomposition of bulk MgH2 in Mg-Ni alloys. We find that the hydrogen release mechanism from bulk (2 µm) MgH2 particles is based on the growth of multiple pre-existing Mg crystallites within the MgH2 matrix, present due to the difficulty of fully transforming all Mg during a hydrogenation cycle whereas, in thin samples analogous to nano-powders, dehydriding occurs by a 'shrinking core' mechanism.

Aluminium phosphide as a eutectic grain nucleus in hypoeutectic Al-Si alloys.

Aluminium phosphide (AlP) particles are often suggested to be the nucleation site for eutectic silicon in Al-Si alloys, since both the crystal structure and lattice parameter of AlP (crystal structure: cubic F43m; lattice parameter: 5.421 A) are close to that of silicon (cubic Fd3m, 5.431 A), and the melting point is higher than the Al-Si eutectic temperature. However, the crystallographic relationships between AlP particles and the surrounding eutectic silicon are seldom reported due to the difficulty in analysing the AlP particles, which react with water during sample preparation for polishing. In this study, the orientation relationships between AlP and Si are analysed by transmission electron microscopy using focused ion-beam milling for sample preparation to investigate the nucleation mechanism of eutectic silicon on AlP. The results show a clear and direct lattice relationship between centrally located AlP particles and the surrounding silicon in the hypoeutectic Al-Si alloy.