Fabrication of Nanocomposite Ceramics by Crystallization of Rapidly Solidified Eutectic Melts

Eutectic melt solidification is shown to avoid cracking during solidification by quenching an amorphous phase. Subsequent annealing results in micro/nanostructure ceramics. This strategy has been applied to HfO₂–Al₂O₃–GdAlO₃ and Y₂O₃–CaO–Al₂O₃ ternary systems that have deep eutectics. In most cases, ceramic materials cracks when they are solidified from melt due to the thermal stress accumulated on the grain boundaries, the large specific volume difference between the melt and the crystalline solid, etc. The main reason why this strategy works is that a eutectic composition yields an amorphous phase from the melts by rapid cooling and the amorphous phase enables to design crystallization without cracking by postannealing. Appropriate postannealing for the quenched amorphous enables to control the crystallization behavior from the amorphous phase, which yields nanostructured composites without cracking. For the HfO₂–Al₂O₃–GdAlO₃ case, the melt solidification and postannealing yields a nanocomposite with high transparency due to reduced scattering of 5–10 nm crystallites. For the Y₂O₃–CaO–Al₂O₃ case, a plate-shaped bulk composite is obtained without cracking by molding the melt and postannealing.     

Source-synchronization and timing vernier techniques for 1.2-GB/sSLDRAM interface

This paper describes a validation system for an SLDRAM interface. The SLDRAM system utilizes two techniques to achieve a high data-transfer rate with a conventional module mounting style. The first technique is a source-synchronization scheme. Since the chip that transmits data also supplies the data clock, the clock and data are completely synchronous. The second is the timing vernier technique. A wait time for output data is programmable in each SLDRAM. Therefore, the time at which data arrive at the controller from any SLDRAM can be set by the controller with a 200-ps step size. The validation chip is designed to emulate these operations. The chip is fabricated using a 0.35-μm CMOS process technology and packaged in a conventional 0.65-mm pitch thin small out-line package, mounted on a single-chip module, and put into an eight-module system. A stub series terminated logic (SSTL)-like interface is adopted for high-speed signals. From system-level measurements, the data eye width of 600 ps is obtained at a data rate of 600 Mbps. Errorless data transmission is observed in both read and write operations in a bit-error rate testing. The validation system has successfully demonstrated a data-transmission rate of 1.2 GB/s (600 Mbit/s/pin) using source-synchronization and timing vernier techniques at the supply voltage of 2.5 V     

Preparation of novel porous solids from alumina-pillared fluorine micas by acid-treatment

New porous solids from alumina-pillared fluorine micas (APMs), which were obtained from synthetic Na-tetrasilicic fluorine mica [NaMg_2.5Si₄O₁₀F₂], were prepared by sulfuric acid-treatment under mild conditions at 25 °C. The products were investigated by XRD, ICP, SEM, TEM and N₂ adsorption–desorption isotherm at 77 K. XRD measurements indicated that the interlayer pillared structure having a large basal spacing collapsed during the early stages of the acid-treatment. ICP analyses indicated that Al³⁺ and Mg²⁺ ions were leached out from the pillared micas during the acid-treatment. The pore properties of the leached products were found to differ from those of the mother pillared micas: the acid leaching of the pillared micas leads to the formation of mesopores around 3.2 nm in diameter. The correlation between the change in pore properties and cation elution behavior suggests that the mesopore formation results from the leaching of Mg²⁺ ions from the octahedral sheet of the pillared micas. The leached products thus obtained retained the flaky morphology of the mother pillared micas. These results show that the mild acid-treatment using APMs provides a novel route for obtaining unique mesopore solids having the large particle sizes of the mother micas.     

Research in Japan on the tracking phenomenon of electricalinsulating materials

This review describes the development and status of tracking research in Japan. First, the fundamentals of tracking and the influences of environmental stresses on tracking will be treated. Then, the principal tracking test methods currently in use will be characterized. Finally, some techniques for improving the tracking resistance of outdoor polymer insulating materials will be discussed     

Determining the relative permeability and conductivity of thin materials

In order to determine the relative permeability and conductivity of thin materials that could not be found using traditional methods, we constructed a shield box and developed a measuring system to estimate the unknown electric parameters of exotic shielding materials such as thin cloths. Thin electromagnetic shielding sheets of both nonmagnetic materials and ferromagnetic materials were used. The shielding effectiveness of the materials was measured as a function of frequency, and the results were compared with the calculated solutions for a multilayered model that was evaluated using the Sommerfeld integral that expresses near-field spherical waves by a composition of cylindrical waves. In these calculations, the relative permeability and conductivity were varied to determine the solution closest to the measured results. The least squares method was used to determine the best fitted values. Initially the nominal values of relative permeability were assumed, and the conductivity was found using the fitting technique. Then this determined value of the conductivity was assumed, and the relative permeability was found using the fitting technique. For the nonmagnetic materials, the estimated relative permeability was the same as the nominal values. For the ferromagnetic materials, the estimated relative permeability varied 0%-30% from the nominal values. For both types of materials, the estimated conductivities were 0%-9.8% different from nominal values. This research details a new method for evaluating the attenuation of interfering electromagnetic waves for thin materials.     

Temporal integration as a function of signal and gap intensity in rats (Rattus norvegicus) and pigeons (Columba livia).

Previous data suggest that rats (Rattus norvegicus) and pigeons (Columba livia) use different interval-timing strategies when a gap interrupts a to-be-timed signal: Rats stop timing during the gap, and pigeons reset their timing mechanism after the gap. To examine whether the response rule is controlled by an attentional mechanism dependent on the characteristics of the stimuli, the authors manipulated the intensity of the signal and gap when rats and pigeons timed in the gap procedure. Results suggest that both rats and pigeons stop timing during a nonsalient gap and reset timing after a salient gap. These results also suggest that both species use similar interval-timing mechanisms, influenced by nontemporal characteristics of the signal and gap. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of carbonization temperature on the basic properties of woodceramics impregnated with liquefied wood

In this paper, a new woodceramics impregnated with liquefied wood is developed and the effect of carbonization temperature on the dimension shrinkage, weight loss, density, compressive strength, and volume electrical resistivity is investigated. The results show that, the higher the carbonization temperature is, the higher the dimension shrinkage is, the higher the compressive strength is, and the lower the electrical resistivity is.     

On-Site Fabrication of Crystalline Cerium Oxide Films and Patterns by Ink-Jet Deposition Method at Moderate Temperatures

Crystalline CeO₂ films and patterns have been successfully fabricated in a "single-step process" at moderate temperature. In this process, the combination of the ink-jet technique and depositing the precursor on a hot substrate (≤300°C) gave crystalline CeO₂ without further heat treatment. X-ray diffraction analysis revealed that the phase formed was crystallized ceria with nanosized (<10 nm) crystallites. The film thickness was several hundred nanometers and the pattern width was about 150 μm. Scanning electron microscopy analysis showed that the films and patterns were free of cracks and adhered to the substrate. This is the first report about the direct patterning of crystalline CeO₂ without postfiring or posttreatments like masking, etching, etc.     

Synthesis of TiN and TiC powders by a reduction/nitridation method using arc image heating

Journal of Materials Science Letters -     

Hydrothermal synthesis of hydroxyapatite whiskers with sharp faceted hexagonal morphology

We report an effective method for the synthesis of hydroxyapatite whiskers with sharp faceted hexagonal shape employing a low temperature (90 °C) hydrothermal route with calcium nitrate tetrahydrate, diammonium phosphate and urea as starting materials. The key parameters of the synthesis process i.e. duration, temperature cycle of the treatment and starting pH value are carefully varied and the end products are investigated using powder X-ray diffraction (XRD), Raman-scattering, infrared spectroscopy (IR), elemental analysis, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), electron diffraction (ED), and high-resolution TEM (HRTEM) in order to find the optimal reaction conditions that lead to the desired hexagonal morphology of HA whiskers. The results demonstrate that gradual and greater increase in solution pH during the hydrothermal process favors large quantity of the single-crystalline hydroxyapatite whiskers with well defined hexagonal morphology.