210Pb-Derived Bioturbation Rates in Sediments Around Seamounts in the Tropical Northwest Pacific

To evaluate bioturbation coefficients (DB) and mixing depths (L), 210Pb and 226Ra activity was measured in two sediments cores (from water depths of 5,398 m and 4,428 m), which were collected from seamount areas in the Northwest Pacific. Using a steady-state diffusion mode, we estimated DB values of 16.8 and 24.1 cm2/a, higher than those in abyssal sediments and those predicted by traditional empirical equations. Corresponding L values varied between 19.3 and 23.1 cm. These high values indicate that seamounts are the area of active bioturbation. A one-dimensional model for the transport of total organic carbon (TOC) from the surface layer of sediments to the deep layer was developed using the distribution pattern of the specific activity of excess 210Pb (210Pbex) and its relationship with TOC. The model showed that the TOC flux transmitted downward by bioturbation was 0.09 mmol/(cm2⋅a) and 0.12 mmol/(cm2⋅a).

Solide State Diffusion Bonding of Al6061-SiC Nanocomposites

Aluminium matrix composites are both strong and lightweight, and are limited in their applications due to the proper choice of welding process. Conventional welding that is based on fusion at the welded joint is not suitable because it leads to the formation of certain defects at the welded joint. For this reason, solid-state welding such as diffusion bonding is one of the suitable joining methods, as there will be no melting of any of the constituents. The solid-state diffusion bonding at 520° C of Al6061-SiC nanocomposites was investigated. This composite material was made by powder metallurgy, where aluminium alloy Al6061 was selected as the base metal, and SiC nanoparticles with an average size of 50 nm were added as reinforced particles. The effects of bonding time on the microstructures and mechanical properties of the welded material were investigated. The main characterisation techniques were optical microscopy, scanning electron microscopy coupled with energy dispersive spectroscopy, x-ray diffraction, and microhardness measurements. We have found that increasing the holding time up to 3 h at 520° C strengthens the weldability of the two basic composite materials and increases their hardness. X-ray diffraction analysis did not reveal any new phase during diffusion welding; it is considered one of the advantages of using the solid-state diffusion welding technique for the assembly of this kind of composite material. The welding success of this composite material widens its field of use, such as the automotive or space industry, because it is a light material with high mechanical properties.

Photoluminescence (PL) properties of NaLi2PO4:Eu3+ phosphor for solid state lighting application

The polycrystalline NaLi2PO4:xEu (x=0.001,0.002,0.005,0.01 and 0.02) phosphors were successfully synthesized via modified solid state diffusion method [MSSDM]. The structural of prepared phosphor was confirmed by using XRD (X-ray diffraction) technique. Additionally, the photoluminescence (PL) behaviors of NaLi2PO4:xEu phosphor was studied.The XRD pattern of prepared phosphor is well matched with JCPDS file.The PL excitation of prepared phosphor was monitored at 618nm while emission was monitored at 393 nm. The effect of different concentrations of Eu3+ ions in NaLi2PO4 phosphor was studies and optimum PL intensity was obtained at x=0.005 mol. of Eu3+ ion. The CIE co-ordinates were calculated and obtained in orange- red region.

The Polarisation Behaviour of Silver in Potassium Hydroxide Solution at Elevated Temperatures

<p>The Polarisation behaviour of silver in 1 mol kg-1 KOH solution over the temperature range 295-478 K was studied using cyclic voltammetry, potentiostatic, galvanostatic and a.c. impedance techniques. Thermodynamic data for the silver/water system at temperatures up to 573 K is presented in the form of potential-pH diagrams which assist in the interpretation of results at elevated temperatures. The cyclic voltammograms and galvanostatic charging curves indicate the principal changes to be the appearance of additional peaks and arrests, respectively, as the temperature is increased, followed by their disappearance at higher temperatures. The data obtained from cyclic voltammetry and also potentiostatic polarisation are analysed in terms of previously-derived relations for limiting rate control, in particular that due to diffusion. The impedance data are examined using equivalent circuit models from which it is shown that surface roughness of the electrodes has a significant effect on the reaction kinetics over the temperature range studied. It is proposed that substantial changes in the electrochemistry of silver at 478 K are associated with extensive surface roughness that a change in the kinetics of growth of the Ag2O multilayer takes place at elevated temperatures with the rate of nucleation of Ag2O growth centres becoming more important in relation to the rate of solid-state diffusion.</p>

The Polarisation Behaviour of Silver in Potassium Hydroxide Solution at Elevated Temperatures

<p>The Polarisation behaviour of silver in 1 mol kg-1 KOH solution over the temperature range 295-478 K was studied using cyclic voltammetry, potentiostatic, galvanostatic and a.c. impedance techniques. Thermodynamic data for the silver/water system at temperatures up to 573 K is presented in the form of potential-pH diagrams which assist in the interpretation of results at elevated temperatures. The cyclic voltammograms and galvanostatic charging curves indicate the principal changes to be the appearance of additional peaks and arrests, respectively, as the temperature is increased, followed by their disappearance at higher temperatures. The data obtained from cyclic voltammetry and also potentiostatic polarisation are analysed in terms of previously-derived relations for limiting rate control, in particular that due to diffusion. The impedance data are examined using equivalent circuit models from which it is shown that surface roughness of the electrodes has a significant effect on the reaction kinetics over the temperature range studied. It is proposed that substantial changes in the electrochemistry of silver at 478 K are associated with extensive surface roughness that a change in the kinetics of growth of the Ag2O multilayer takes place at elevated temperatures with the rate of nucleation of Ag2O growth centres becoming more important in relation to the rate of solid-state diffusion.</p>

Effect of Post-Weld Heat Treatment on the Solid-State Diffusion Bonding of 6061 Aluminum Alloy

The precipitation-hardenable aluminum alloy 6061 (AA 6061) is favored for aerospace components and automotive parts. However, the tenacious oxide layer on the surface greatly limits the quality and applicability of joining AA 6061. In this study, the joining method of solid-state diffusion bonding was implemented for AA 6061 plates, and the effects of post-weld heat treatment (PWHT) on the joint interface were investigated. The bonding temperatures were within the range of 500–530 °C, and the time periods varied from 30 to 240 min under a static pressure of 5 MPa in a vacuum. The diffusion bonded specimens were subjected to T4- and T6-PWHT to improve the bonding quality. The interfacial microstructure of the joints was analyzed by scanning electron microscopy, and the mechanical properties were evaluated with shear tests. The experimental results showed that the shear strength of the diffusion bonded joint could reach around 71.2 MPa, which was highly dependent on bonding temperature and holding time, and T6-PWHT further enhanced it to over 100 MPa. The effects of PWHT on the diffusion bonded AA 6061 joint were investigated, and the fractography on the sheared surfaces indicated that PWHT-T6 played an important role in enhancing joint strength, which was consistent with the measured shear strength. The sequential PWHT for AA 6061 after diffusion bonding was proven to be feasible for bonding of AA 6061 parts, and the joint strength was sufficient for industrial needs.

Improving Nonenzymatic Biosensing Performance of Electrospun Carbon Nanofibers Decorated With Ni/Co Particles via Oxidation

Electrochemical nonenzymatic biosensors with no immobilization and degradation problem, have recently attracted growing attention due to stability and reproducibility. Here, a comparative study was conducted to precisely evaluate the nonenzymatic glucose sensing of pure/oxidized Ni, Co, and their bimetal nanostructures grown on electrospun carbon nanofibers (ECNFs). This method provides a low-cost free stand electrode. The prepared nanostructures with superb physiochemical features exhibited sensitivity (from 66.28 to 610.6 μA mM−1 cm−2), linear range of 2-10 mM, limit of detection in the range of 1 mM, and response time (<5 s), besides outstanding selectivity and applicability for glucose detection in the human serum. Regarding Co-C and Ni-C phase diagrams, solid-state diffusion phenomena, and rearrangement of dissolved C atoms after migration from metal particles was discussed. This study undoubtedly provides new prospects on nonenzymatic biosensing performance of mono-metal, bimetal, and oxide compounds of Ni and Co elements, which is useful for the fabrication of biomolecules detecting devices.