Joining of Hypereutectic Al-50Si Alloys Using Lead-Free Brazing Filler Glass in Air

Hypereutectic Al-Si alloys are attractive materials in the fields of electronic packaging and aerospace. A Bi2O3-ZnO-B2O3 system lead-free brazing filler glass was employed to braze hypereutectic Al-50Si alloys in air. The hypereutectic Al-50Si alloys were pre-oxidized and the low-temperature glass powder was flake-shaped in the brazing process. The effects of brazing temperature and time on joints microstructure evolution, resulting mechanical strength, and air tightness were systematically investigated. The results indicated that the maximum shear strength of the joint was 34.49 MPa and leakage rate was 1.0 × 10−10 Pa m3/s at a temperature of 495 °C for 30 min. Crystalline phases, including Bi24B2O39 and Bi2O3, were generated in the glass joint. The formation of a diffusion transition layer with a thickness of 3 μm, including elements of Al, Si, Zn, Bi, Na, and B, was the key to form an effective joint. The elements of Al, Si, and Bi had a short diffusion distance while the elements of Zn, Na, and B diffused in a long way under brazing condition.

Direct Observation of Long Electron-Hole Diffusion Distance in CH3NH3PbI3 Perovskite Thin Film

In high performance perovskite based solar cells, CH3NH3PbI3 is the key material. We carried out a study on charge diffusion in spin-coated CH3NH3PbI3 perovskite thin film by transient fluorescent spectroscopy. A thickness-dependent fluorescent lifetime was found. By coating the film with an electron or hole transfer layer, [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) or 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (Spiro-OMeTAD) respectively, we observed the charge transfer directly through the fluorescence quenching. One-dimensional diffusion model was applied to obtain long charge diffusion distances in thick films, which is ~1.7 μm for electrons and up to ~6.3 μm for holes. Short diffusion distance of few hundreds of nanometer was also observed in thin film. This thickness dependent charge diffusion explained the formerly reported short charge diffusion distance (~100 nm) in films and resolved its confliction to thick working layer (300–500 nm) in real devices. This study presents direct support to the high performance perovskite solar cells and will benefit the devices’ design.

Hierarchical dispersed multi-phase nickel cobalt oxide mesoporous thorn microspheres as superior rate anode materials for lithium ion batteries

The short diffusion distance, large active area for Li+, the suppressed side reaction and volume change make the dispersed multi-phase nickel cobalt oxide porous thorn microspheres exhibit superior rate and cyclic properties.

Optimization of AC Electrokinetic Mixing by Nanocomposite Monolayer

The mixing of fluids using AC Electrokinetic is presented in this paper. Both AC electrothermal (ACET) and AC electroosmosis (ACEO) techniques are investigated for mixing operation. AC electrokinetic mixing utilizes the characteristics of short diffusion distance and large specific interface area, and the characteristics of laminar flow and multiphase flow in a microchannel. The proposed mixer will have advantages of easy implementation and compatibility with microchip fabrication. Furthermore low and high conductive fluid has been experimented for mixing operation. In this research, the ACET and ACEO mixing will be optimized by surface modification using a biocompatible hydrophobic nanocomposite monolayer. This coating will modify the mixer surface to a hydrophobic surface and improve the friction losses at the interface, and eventually increase the mixing rate. Both ACEO and ACET flow is a promising technique in microfluidic mixing toward laboratory automation applications, such as clinical diagnostics and high-throughput drug screening. But the mixing efficiency and type of AC electrokinetic usage depends on the conductivity range of the fluids. These mixers can be integrated with the lab-on-a-chip and can provide inexpensive disposable devices.

Synthesis and Electrochemical Properties of V2O5 Nanostructures

In this seminar, I will present our recent work on the growth and electrochemical properties of single crystalline vanadium pentoxide (V2O5) nanorod and Ni-V2O5·nH2O nanocable arrays. These nanostructures were prepared by solution synthesis and template-based electrodeposition. Processing, morphology, structure and electrochemical properties of these nanostructures will be discussed. These nanostructured electrodes of vanadium pentoxide demonstrate significantly enhanced intercalation capcity and charge/discharge rate compared to the plain film electrodes, due to the high surface area and short diffusion distance offered by nanostructure.

The Effect of Initial Activation on Microstructures of Mg/Cu Super-laminates and Hydrogen Absorption Properties

Microstructures and hydrogen storage properties of Mg/Cu super-laminates were compared to clarify the effect of initial activation. The initial activation change micro/nano-structures of Mg/Cu super-laminates into Mg2Cu with layered structure in fine grain size of about 1μm and pores highly dispersed between layers in sub-micrometer size. Large surface area, dense defects and short diffusion distance for the reaction enable Mg/Cu super-laminates to absorb hydrogen very quickly.

Synthesis and Electrochemical Properties of InVO4 Nanotube Arrays

A capillary-enforced template-based method is described for the preparation of InVO4 nanotube arrays. Nanotube arrays of InVO4 were prepared by filling the InVO4 sol into pores of polycarbonate membranes and pyrolyzing through sintering. Another type of InVO4 nanotube arrays (InVO4/acac) are obtained from the sol with the addition of acetylene acetone (acac). For comparison purposes, InVO4 films were prepared by drop casting from InVO4 same sol. Films and the two types of nanotube arrays of InVO4 annealed at 500°C consist of mixed monoclinic (InVO4-I) and orthorhombic (InVO4-III) phases. Scanning electron microscopy (SEM) characterizations indicate that the nanotubes are well-aligned, perpendicular to substrate surface with the outer diameter of ~200 nm for short InVO4 nanotubes and ~170 nm for long InVO4 nanotubes. Chronopotentiometry results reveal that InVO4/acac nanotube array has the highest charge capacity (790 mAh/g), followed by InVO4 nanotube array (600 mAh/g) then InVO4 film (290 mAh/g). Such enhanced lithium-ion intercalation properties are ascribed to the large surface area and short diffusion distance offered by nanostructures and amorphisation caused by acetylene acetone in the case of InVO4/acac nanotube arrays.

Age-dependent changes in contraction and regional myocardial myosin heavy chain isoform expression in rats

The goals of this study were to measure the relative levels of the α- and β-isoforms of myosin heavy chain (MHC-α and MHC-β, respectively) in multiple, specific regions of the adult rat heart and to determine whether age-dependent changes in isoform levels in different regions are uniform. Relative amounts of MHC-α and MHC-β were determined in right and left atria and left ventricular (LV) Purkinje fibers (PF), papillary muscles, trabeculae, and endo-, mid-, and epicardial regions at 2, 5, 10, 16, and 21 mo. PFs contained substantial amounts of myosin and were striated and capable of generating force and shortening on activation. Levels of MHC-β increased in all LV compartments with age, especially between 2 and 5 mo. There was more MHC-β in PFs than other LV sites. There were regional differences in the level of MHC-β throughout the LV at all ages, and the rates of change within regions differed. Ca2+-activated tension in PFs and trabeculae was compared at 2 and 22 mo. PF tension was less than trabecula tension, and this difference may be explained by differences in MHC content. Vmax and tension-generating ability in PFs decreased with age. Maximal tension generated by trabeculae did not change during aging. A large proportion of the increase in the level of MHC-β that is normally associated with aging occurs at a relatively early age in rat LV. PFs, with their small diameters and short diffusion distance, should be considered for skinned multicellular myocardial studies.