High-temperature oxidation of pure titanium in CO2 and Ar-10%CO2 atmospheres

The oxidation behavior of pure titanium has been investigated in the temperature range of 1000 K to 1300 K in CO₂ or Ar-10%CO₂. Optical microscopy, electron probe microanalyses, and X-ray measurements on the oxide scales formed during oxidation indicate that their structures are nearly independent of temperature and the corrosion atmosphere. The scales consisted of two layers, an external one and an internal one, having a rutile (TiO₂) structure. The parabolic rate law was confirmed for growth of the external scale and the permeation depth of oxygen in titanium with apparent activation energies of 266 and 226 kJ/mol, respectively. The rate-determining diffusion species in the oxidation processes are discussed.     

Probability of precision micro-machining of insulating Si3N4 ceramics by EDM

Electrical discharge machining (EDM) is used as a precision machining method for the electrically conductive hard materials with a soft electrode material. But recently we succeeded to machine on insulating material by EDM. The technology is named as an assisting electrode method. The EDMed surface is covered with the electrical conductive layer during discharge. The layer holds the electrical conductivity during discharge. For micro-EDM, the wear of tool electrode becomes lager ratio than the normal machining. So the micro-machining is extremely difficult to get the precision sample.

In this paper to obtain a fine and precise ceramics sample, some trials were carried out considering the EDM conditions, tool electrodes material and assisting electrode materials. Insulating Si₃N₄ ceramics were used for workpiece. The machining properties were estimated by the removal rate and tool wear ratio. To confirm the change of micro-machining process, the discharge waveforms were observed. The micro-machining of the Ø0.05 mm hole could be machined with the commercial sinking electrical discharge machine.     

Micromachining of electroformed nickel mold using thick photoresist microstructure for imprint technology

In order to fabricate polymer-based microstructures with feature sizes on the order of micrometers, we have been developing a microimprint technology with a fine nickel (Ni) mold instead of a conventional photolithography technique. The Ni mold was successfully fabricated by electroforming using a positive thick photoresist microstructure patterned on a silicon substrate as a replication master. The photoresist microstructure with excellent edge quality can be obtained under irradiation with single wavelength (g line) selected from a high-pressure mercury lamp. In addition, its sidewall angle in the range of 65° to 84° can be controlled precisely by varying the distance between a photomask and a photoresist surface. On the structured photoresist master, Ni was electroplated up to a thickness of about 110 μm, and then removed from the master. In this process, two-step electroplating at different current densities was carried out in order to prevent deformation of the photoresist master due to stress generated in a Ni electrodeposit. With the Ni mold, fine patterns with a width of 10 or 30 μm and a depth of 24 μm were almost completely transferred to polymetric materials (PMMA). The geometrical dimensions of the fabricated PMMA microstructures were found to be only about 10% reduction against the Ni mold.     

Remarks on the tracking method of neural network weight change for a learning-type neural network feed-forward feed-back controller

Although many neural network controllers have been proposed, we still have to tune several parameters of neural networks in order to obtain a better learning performance in practical applications. Our tracking method provides a new aspect of this tuning of neural network parameters. It has been applied to adaptive and learning-type neural network direct controllers, and an adaptive-type neural network feed-forward feed-back controller. This work applied it to a learning-type neural network feed-forward feed-back controller. Simulation results confirmed its usefulness, and we discuss a transformation of the track on a 2D plane to one-dimensional values.     

Microstructure and properties of (Sr, Ca)CuO2/(Sr, Ca)RuO3 multilayers

Epitaxial multilayer thin films of infinite-layer (Sr, Ca)CuO₂ and perovskite (Sr, Ca)RuO₃ have been prepared on (100) SrTiO₃ substrates by multitarget rf magnetron sputtering. X-ray diffraction analyses revealed that the multilayer structure of (Sr, Ca)CuO₃/(Sr, Ca)RuO₃ was successfully fabricated with a minimum layer thickness of 20 Å. Transmission electron microscopy measurements of the multilayers indicated that there was no dislocation which normally exists in single-layer films with an infinite-layer structure. Resistivities of multilayer films at room temperature ranged from 1 to 10 m cm and showed semiconductor-like dependence against the temperature.     

Probabilistic calibration of discrete element simulations using the sequential quasi-Monte Carlo filter

The calibration of discrete element method (DEM) simulations is typically accomplished in a trial-and-error manner. It generally lacks objectivity and is filled with uncertainties. To deal with these issues, the sequential quasi-Monte Carlo (SQMC) filter is employed as a novel approach to calibrating the DEM models of granular materials. Within the sequential Bayesian framework, the posterior probability density functions (PDFs) of micromechanical parameters, conditioned to the experimentally obtained stress–strain behavior of granular soils, are approximated by independent model trajectories. In this work, two different contact laws are employed in DEM simulations and a granular soil specimen is modeled as polydisperse packing using various numbers of spherical grains. Knowing the evolution of physical states of the material, the proposed probabilistic calibration method can recursively update the posterior PDFs in a five-dimensional parameter space based on the Bayes’ rule. Both the identified parameters and posterior PDFs are analyzed to understand the effect of grain configuration and loading conditions. Numerical predictions using parameter sets with the highest posterior probabilities agree well with the experimental results. The advantage of the SQMC filter lies in the estimation of posterior PDFs, from which the robustness of the selected contact laws, the uncertainties of the micromechanical parameters and their interactions are all analyzed. The micro–macro correlations, which are byproducts of the probabilistic calibration, are extracted to provide insights into the multiscale mechanics of dense granular materials.     

Deformation and Fracture of Micron‐Sized Metal‐Coated Polymer Spheres: An In Situ Study

In situ imaging and analysis of the mechanical behavior of micron‐sized metal‐coated polymer particles under compression is reported. A nanoindentation set‐up mounted in a scanning electron microscope is used to observe the deformation and fracture of 10 μm polymer spheres with Ni, Ni/Au, Au, and Ag coatings. The spheres fracture in one of two metallization‐dependent modes, brittle, and ductile, depending only on the presence of a nickel layer. The metal coating always fractures parallel to the direction of compression. The mechanical properties up to the point of coating fracture are rate‐dependent due to the viscoelastic polymer core. Metal‐coated polymer spheres are an important composite material in electronics packaging, and this study demonstrates a novel method of evaluating the mechanical properties of particles to tailor them for electronic materials.

     

Single-crystal growth and characterization of Cu2O and CuO

We have prepared a large number of crystals of cuprous oxide (Cu2O) by various procedures. Photoluminescence spectra of these crystals were studied to examine the concentration of defects, especially copper vacancy VCu to seek favourable conditions for growing Cu2O crystal. High-quality single crystals of Cu2O were prepared by the floating-zone melting method in air. Several synthetic crystals (specimens FA, FZ and GZ) and also a natural crystal were studied by X-ray analysis, inductively coupled plasma spectroscopy analysis, optical absorption, photoluminescence, photoconductivity and cyclotron resonance absorption, photoluminescence, photoconductivity and cyclotron resonance absorption to characterize their optical and electrical qualities. The best values of mobility and scattering time of photocarriers at T = 4.2 K are estimated to be h1.8 × 105 cm2 V–1 s–1 and h60 ps for positive holes, and 1.3 × 105 cm2 V–1 s–1 and 70 ps for electrons in Cu2O. Further, we report preliminary experimental results on transport property of crystals also of cupric oxide (CuO) purified by the floating-zone melting method.