Molten-Salt Synthesis and Characterization of Nickel-Doped Forsterite Nanocrystals

Nickel-doped forsterite (Ni²⁺:Mg₂SiO₄) nanocrystals have been synthesized by a facile molten-salt approach in the presence of NaCl and a surfactant (NP-7.5). The products were characterized by X-ray diffraction, transmission electron microscopy (TEM), high-resolution TEM, selected area electron diffraction (SAED), and luminescence spectra measurements. The crystal size could be controlled by tailoring the synthesis parameters. TEM, high-resolution TEM, and SAED results revealed the single crystalline character of Mg₂SiO₄ nanoparticles. A possible model for the growth of Ni²⁺:Mg₂SiO₄ nanocrystals was postulated. The obtained Ni²⁺:Mg₂SiO₄ nanocrystals show strong, super broad, near-infrared luminescence at room temperature. These doped Mg₂SiO₄ nanocrystals are promising gain mediums for super broadband optical amplification.     

Preparation of a crosslinked polyelectrolyte membrane for fuel cells with an allyl methacrylate based two‐step reaction

In this study, a proton‐exchange membrane for fuel cells was prepared via a two‐step reaction with an allyl methacrylate (AMA) as an asymmetric crosslinking agent. First, a linear‐chain polymer was synthesized, consisting of hydrophilic 2‐acrylamido‐2‐methylpropanesulfonic acid (AMPS), hydrophobic 2,2,2‐trifluoroethyl methacrylate (TFEMA), and AMA. Subsequently, we crosslinked the linear‐chain polymer by reacting the remaining allyl group during dry heating. The proton conductivity of the prepared membrane was 7 × 10^?2 S/cm at room temperature. The membrane was characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, and atomic force microscopy. The polymer electrolyte membrane fuel cell (PEMFC) performance was evaluated for a membrane electrode assembly composed of the crosslinked AMPS–TFEMA–AMA/ fluoroalkyl graft polymer (FGP) membrane. As a result of a power‐generation test, a maximum power density of 174 mW/cm² at a current density of 400 mA/cm² was observed for a PEMFC single cell. Consequently, it was confirmed that the AMPS–TFEMA–AMA/FGP membrane for PEMFC could easily be prepared via a two‐step reaction at a low cost and that PEMFC exhibited a cell performance and that of cells with the Nafion membrane. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Direct Observation of Crack Tip Geometry of SiO2 Glass by High-Resolution Electron Microscopy

Crack tips in thin SiO₂ glass films were observed directly by high-resolution/high-voltage electron microscopy. An elliptical crack with radius of curvature ∼ 1.5 nm was observed. When the glass film with the crack was soaked in water at 90°C for 7 d, the crack tip became blunt by a process of dissolution and precipitation.     

Plasma polymerized membranes and gas permeability. I

Gas permeability of composite membrane prepared by plasma polymerization of various organic compounds was studied. In the membrane, a pinhole-free polymeric thin film was formed on a porous substrate. This film below 0.2 μm in thickness had sufficient mechanical strength for gas separation. The composite membranes were recognized to have high permeability and high permselectivity. Especially, the membranes prepared from hexamethyldisiloxane showed high permeation rate for oxygen, and those prepared from 1-hexene or cyclohexane showed high permselectivity between oxygen and nitrogen. chemical structure of plasma-polymerized film prepared from hexamethyldisiloxane was similar to that of dimethylpolysiloxane with a crosslinking of the polymer. The high permeability and high permselectivity of this film is considered to be due to its structure as mentioned above.     

Thermochromic properties and low emissivity of ZnO:Al/VO2 double-layered films with a lowered phase transition temperature

We studied the optical and semiconductor-metal (S-M) transition properties of ZnO:Al/VO₂/substrate double-layered films that consisted of a ZnO:Al top layer and a VO₂ bottom layer. ZnO:Al and VO₂ films were grown on fused silica substrates by radio frequency magnetron sputtering and polymer-assisted deposition, respectively. The ZnO:Al/VO₂/substrate films displayed low emissivity (0.31-0.32) with integrated luminous transmittance (T_lum>46%) and thermochromic properties (ΔT_sol>4.1%). The low emissivity and thermochromic properties were independently introduced by the transparent conductive ZnO:Al layer and the VO₂ layer. In addition, the S-M transition temperatures for VO₂ shifted to lower temperatures after the ZnO:Al deposition process, which was due to the formation of surface nonstoichiometry—oxygen deficiency that was induced by the ZnO:Al deposition process.     

Polymeric materials having a porous structure prepared by radiation polymerization

Polymeric materials having a porous structure were prepared by radiation polymerization of 2-hydroxyethyl methacrylate-water system at various temperatures, and its nature was studied. The materials prepared at low irradiation temperatures below about –20°C had a cylindrical (continuous) pore structure, and those at high irradiation temperatures 0°C had a noncontinuous pore structure. The pore size varied with radiation polymerization conditions such as monomer concentration, irradiation temperature etc. The orientation of the pore in the materials prepared at low irradiation temperatures was observed.     

Hot hardness of (Fe,Cr)3C and (Fe,Cr)7C3 carbides

Hot hardness was measured on the primary carbides, (Fe, Cr)₃C and (Fe, Cr)₇C₃, in unidirectionally solidified iron-carbon-chromium hypereutectic alloys with chromium more than 4.8 wt %. The hardness-temperature relation was represented by two Ito-Shishokin formulae,H _v =A(— BT), and thus was drawn by two lines on a semilogarithmic graph. The inflection temperature where the two lines intersected was found at 730 to 860 K for (Fe, Cr)₃C carbide containing 0 to 14 wt % Cr, increasing with an increase in the chromium concentration in the carbide, and at about 910 K for (Fe, Cr)₇C₃ carbide containing 36 to 76 wt % Cr. With increasing chromium concentration in each carbide, the hardness of the carbide increased and the thermal softening coefficients decreased. The effect of chromium on the hardness, the inflection temperature and the thermal softening coefficients was more pronounced for (Fe, Cr)₃C carbide than for (Fe, Cr)₇C₃ carbide. Each of the thermal softening coefficients,B ₁(T<T _t),B ₂(T>T _t), the inflection temperature,T _t, room-temperature hardness,H _v(T _RT), and the hardness atT _t,H _v(T _t), related linearly to the chromium concentration in the carbides, and hence the hot hardness of the carbides could be expressed as functions of temperature and chromium concentration in the carbides. The relationships betweenH _v(T _RT) andH _v(T _t) and between the thermal softening coefficient,B ₂, and the activation energy for creep,Q _c(kJ mol^–1), were represented by the following equations:H _v(T _t)0.7H _v(T _RT),B ₂=1.26/Q _c.     

Wheel/rail contact geometry on tight radius curved track: simulation and experimental validation

In this investigation, a numerical procedure for wheel/rail one and two-point contact geometry analysis is developed for predicting the location of contact points in curved negotiations on a tight radius curved track. The proposed method accounts for the change in the longitudinal location of contact point along the curved track as well as the circumferential contact point on the wheel flange. For the purpose of validation, simulation results for one and two-point contact scenarios are compared with those obtained using the experiment. The experiment is performed on a test track of R48 curve using an actual truck, and the location of contact points for given lateral and yaw displacements are measured on the tight radius curved track. It is demonstrated that good agreements are obtained between the simulation and experimental results in tread and flange contacts.