Melting behavior of MgO-based inert matrix fuels containing (Pu,Am)O2−x

The melting behavior of MgO-based inert matrix fuels containing (Pu,Am)O_2−x ((Pu,Am)O_2−x-MgO fuels) was experimentally investigated. Heat-treatment tests were carried out at 2173 K, 2373 K and 2573 K each. The fuel melted at about 2573 K in the eutectic reaction of the Pu-Am-Mg-O system. The (Pu,Am)O_2−x grains, MgO grains and pores grew with increasing temperature. In addition, Am-rich oxide phases were formed in the (Pu,Am)O_2−x phase by heat-treatment at high temperatures. The melting behavior was compared with behaviors of PuO_2−x-MgO and AmO_2−x-MgO fuels.     

Fabrication and characterization of porous ZrO2 with a high volume fraction of fine closed pores

A novel technique for the fabrication of porous ZrO₂ with a high volume fraction of fine closed pores was investigated. A partially stabilized ZrO₂ (3 mol% Y₂O₃; Y-PSZ) body, with a 97–99% relative density and containing a small amount of impurities, exhibited a large volume expansion related to the formation of closed pores after heating at 1700 °C for 10 min in N₂. These closed pores seemed to mainly form due to the vaporization of hydroxyl apatite: Ca₁₀(OH)₂(PO₄)₆ as an impurity and superplasticity of the ZrO₂ during heating. Porous ZrO₂ with approximately 24.6% closed pores (total porosity: 26.7%) was successfully fabricated by the addition of 1 mass% SiO₂, 1 mass% TiO₂, and 1 mass% hydroxyl apatite. The closed pore size and morphology of the resultant porous ZrO₂ bodies were investigated, and the formation mechanism of the closed pores was examined on the basis of chemical thermodynamics.     

Alcohol electrooxidation at Pt‐Ru sputter‐deposited electrode

The use of various alcohols including methanol has been considered as the fuel of direct alcohol fuel cells (DAFCs). Thus far, the Pt alloys have mainly been studied as anode electrocatalysts for DAFCs. Pt itself is poisoned by chemical species produced during the alcohol oxidation. There exist many reports that the addition of Ru is effective for alcohol oxidation. In this work, we prepared a Pt‐Ru co‐sputtered electrode by changing the Ru content, sputtering time, and Ar pressure for the sputtering. By using the prepared electrocatalysts, relationships between sputtering conditions and electrocatalytic activity were measured for some alcohols. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 163(2): 14–21, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20594     

Mapping of extended defects in B-doped (001) homoepitaxial diamond films by electron-beam-induced current (EBIC) and cathodoluminescence (CL) combination technique

We have studied on a spatial distribution of extended defects with shell-shape pits in B-doped (001) homoepitaxial diamond films using electron-beam-induced current (EBIC) and cathodoluminescence (CL) combination technique. The EBIC image corresponded to the comprehensive one of band-A emission (430 nm) in CL measurements. In addition, both EBIC and CL images also corresponded to optical microscope image (Nomarski) with shell-shape pits. These experimental results indicate that the shell-shape pits are accompanied with localized electrically-active-defects originating from extended defects such as dislocation with band-A CL emission. It is suggested that extended defects such as dislocations result in the formation of shell-shape pits.     

Effect of Grain Contiguity on the Thermal Diffusivity of Aluminum Nitride

Thermal diffusivity of AlN-based ceramics was studied as a function of second-phase amount and heat-treatment time. The Y₂O₃·Al₂O₃ contents varied over the range of 13-31 vol%. The thermal diffusivity decreased as the amount of second phase increased. After sintering at 1850°C, the AlN ceramics consisted of rounded, largely isolated grains. Heat treatment of these samples for 5-50 h at 1800°C resulted in microstructures that consisted of largely contiguous AlN grains. There was a substantial increase in the thermal diffusivity after the heat-treatment step, and the incremental improvement was essentially constant for the three compositions that have been studied. The amount of second phase was unchanged during heat treatment; therefore, the increase in thermal diffusivity is assumed to be a direct result of the enhanced contiguity of AlN grains.     

Thermal Conductivity of ß-Si3N4: I, Effects of Various Microstructural Factors

Calculations based on a simple modified Wiener's model for thermal conductivity of a composite material predict that the thermal conductivity of ß-Si₃N₄ decreases quickly as the grain-boundary film thickness increases within a range of a few tenths of a nanometer and also that it initially increases steeply with increased grain size, then reaches almost constant values. Because of the faceted nature of the ß-Si₃N₄ crystal, the "average" grain-boundary film thickness is much greater than that in equilibrium. The present study demonstrates both theoretically and experimentally that grain growth alone cannot improve the thermal conductivity of ß-Si₃N₄.     

The selective formation of unsaturated alcohols by hydrogenation of α,β-unsaturated aldehydes in supercritical carbon dioxide using unpromoted Pt/Al2O3 catalyst

When α,β-unsaturated aldehydes are reduced by hydrogen in supercritical carbon dioxide using an unmodified Pt/Al₂O₃ catalyst, unsaturated alcohols are highly selectively produced, in contrast to previous results with organic solvents in which such a selective hydrogenation is difficult to achieve with monometallic Pt catalysts. The selectivity of unsaturated alcohols depends mainly on pressure of carbon dioxide while the conversion depends on both carbon dioxide and hydrogen pressures. The selectivity increases with increasing pressure and then does not change so much at higher pressures. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hydrogen-induced phase transformation

Hydrogen-induced amorphization (HIA) of intermetallic compounds was simulated by the molecular dynamics (MD) method using pairwise potentials. The microscopic mechanism of HIA in AB₂ C15 Laves phase compound is discussed. The hydrogenation causes elastic softening in the bulk modulus and induces elastic instability. A phase transformation by elastic instability follows paths with minimal activation barriers, and nonequilibrium transformations including amorphization can be realized. The HIA can be considered as a case. The key to induce HIA is the expansion of the B atoms in a Laves phase; it facilitates the instability of the sublattice of B atoms. If the amount of hydrogen exceeds a critical value, HIA occurs. The HIA is a potential-driven phase transformation, and the resultant amorphous structure is potentially favored over the hydrogenated crystal. We also report the fracture process by isotropic loading and compare it to HIA.