Electrical conductivities of M3P2O8 (M = Ca,Ba)

Two-probe conductivity measurements made for M₃P₂O₈ (M = Ca, Ba) suggested that the electrical conduction of these phosphates would primarily be due to the migration of Ca²⁺ and Ba²⁺ ions. At relatively low temperatures and high oxygen partial pressures, in contrast to Ca₃P₂O₈, however, Ba₃P₂O₈ shows partial electronic conduction.     

System identification theory of the thermal network model and an application for multi-chamber airflow measurement

A comprehensive theory of multi-chamber air infiltration measurement using a single tracer gas is introduced from the general stand point of system identification. The thermal network model can be applied not only to the temperature transfer and diffusion system but also to the tracer gas transfer system. This model is formulated mathematically in a state equation. The coefficients in the state equation represent airflow rates of infiltration. Two theories for estimating these coefficients are deduced from the least square. These are batch and successive identification. Further, the evaluation method of estimation errors that has been so far insufficient is described. Finally, the accuracy and the practicality of the theory are confirmed by the actual measurement system and experiments.     

Synthesis and properties of platinum-dispersed carbon by pressure pyrolysis of organoplatinum copolymer

Platinum-dispersed carbon was synthesized by pressure pyrolysis of divinylbenzenebis (2-allylphenyl)platinum (APPt) and phenylacetylene-APPt at 550 °C and 125 MPa. The crystallinity of platinum dispersed in the carbon matrix synthesized from phenylacetylene(PA)-APPt was higher than that from divinylbenzene(DVB)-APPt. Platinum particles less than 60 nm were dispersed in the carbon matrix synthesized from DVB-APPt at 550 °C and 125 MPa. The carbon matrix formed from PA-APPt contained platinum particles of about 120 nm. The specific area of platinum-dispersed carbon synthesized at 550 °C and 125 MPa increased on subsequent heat treatments in argon, and reached 90 m² g^–1 after heat treatment at 800 °C for 1 h. The activity of platinum-dispersed carbon for the hydrogenation of cyclohexene increased with increasing specific area. Platinum-dispersed carbon formed from DVBAPPt was more active for hydrogenation reaction than that from PA-APPt. The highly active platinum-dispersed carbon could be synthesized from DVB-APPt at 520 °C. The surface area reached 154 m² g^–1 after heat treatment at 800 °C.     

Interfacial layer in homoepitaxial InP grown by organometallic vapor phase epitaxy with TMIn and TBP

The effects of interfacial layers with high impurity concentration on the properties of homoepitaxial InP layers have been studied by far-infrared (FIR) magnetoabsorption, in addition to dc mobility, Hall effect, and photoluminescence (PL) measurements. The layers are grown by organometallic vapor phase epitaxy with trimethylindium and tertiarybutylphosphine. Impurity absorption as well as cyclotron resonance is observed in the FIR measurements. Variations in the intensity of the resonance signals and the mobilities obtained from the linewidths of the cyclotron resonance are interpreted by a double layer model, i.e. a bulk layer with an interfacial layer. Carrier concentrations, dc mobilities, and PL intensities of both bound excitons and free excitons are also explained by the model.     

High oxide ion conduction in sintered oxides of the system Bi2O3-WO3

The ionic conduction in sintered oxides of the system Bi₂O₃-WO₃ was investigated by measuring conductivities and ion transference numbers under various conditions. The ion transference number was measured by an oxygen concentration cell employing the specimen tablet as the electrolyte.It was found that a compound 3Bi₂O₃ WO₃ and its solid solution were high oxide ion conductors, the conductivities of which were about one order of magnitude higher than those of the well-known oxide ion conductors such as stabilized zirconias. In contrast to pure Bi₂O₃ which is a completely electronic conductor below 730°C, these materials showed high oxide ion conduction even below 700°C accompanied by little electronic conduction. 3Bi₂O₃ WO₃ has the face centered cubic structure, probably of the fluorite type, and the oxide ion conduction was thought to be attributed to the migration of oxide ion vacancies in the crystal.     

Improvement of dispersion stability and characterization of upconversion nanophosphors covalently modified with PEG as a fluorescence bioimaging probe

Upconverting (UC) phosphors (UCPs) are ceramic materials doped with rare earth ions. These materials can absorb and upconvert infrared (IR) radiation to emit visible light by the stepwise excitation among discrete energy levels of the rare earth ions. UCPs are potentially useful reagents for use in bioimaging since the use of low energy photons avoids photo-toxicity. The use of UCP nanoparticles as bioimaging probes requires surface modifications in an effort to improve dispersion stability in aqueous milieu. In this study, we covalently attached poly(ethylene glycol) (PEG) to the surface of Er-doped Y₂O₃ nanoparticles and firstly demonstrated that PEG covalently bound to the Y₂O₃ surface markedly improved dispersion stability in water. UC emission of PEG-modified Er–Y₂O₃ nanoparticles excited with IR light was successfully observed. We also showed that PEG-modified Er–Y₂O₃ nanoparticles exhibit no cell-toxicity. These observations lend strong support to the potential use of PEG-modified UCP nanoparticles as bioimaging tools.     

Consolidation of SiC/BN composite through MA-SPS method

Hexagonal-BN has been selected as a second phase for SiC/BN composite to improve SiC’s machinability and thermal shock resistance. In this research, nano-metric SiC/BN was prepared through mechanical alloying (MA) from Si + C + BN powder and then consolidated by SPS without any sintering aids. XRD results after MA revealed the absence of sharp peaks corresponding to SiC and BN. The density and the intensity of the SiC and BN peaks on XRD increased with temperature during SPS. The final density of the composite reached approximately 90–99% with 50/50 of SiC/BN to 100/0. During the consolidation process, crystallization, phase separation, and ordering were observed simultaneously. This phenomenon could accelerate the mass transfer for the consolidation and the preparation of bulk SiC/BN composite without any sintering aids. In a 50/50 SiC/BN ratio, the Vickers hardness of the nano-structured reference sample prepared by the conventional method with sintering aids could not be measured due to high porosity. However, the well-consolidated sample prepared in our research showed a hardness of approximately 3 GPa.     

Interlayer dissolution of montmorillonite observed by internal refraction interferometry

Dissolution behavior of a clay mineral such as montmorillonite is one of the most important phenomena for a long-term safety of high-level radioactive waste disposal. Dissolution rates of aggregated montmorillonite samples in basic solutions at room temperature were investigated in flow-through experiments by using internal refraction interferometry with an enhanced phase-shift interferometry. Conventional solution analysis methods cannot measure the effects of dissolution occurring within the interlayer of montmorillonite. Internal refraction interferometry can measure the crystal dissolution of montmorillonite, including both the dissolution of the outer surface and the interlayer of montmorillonite. The dissolution rate of montmorillonite in the interlayer was first observed. It was slower than the dissolution rate of outer surface. As the number of the montmorillonite crystal laminations increased, the montmorillonite dissolution rate in the interlayer decreased. Montmorillonite dissolution rates showed limited dependence on pH in the alkaline solutions. This can be explained by the effect of the laminated structure of montmorillonite crystal on the dissolution rate, especially in highly alkaline solution.     

Effects of α-radiation on a direct disposal system for spent nuclear fuel – (2) review of research into safety assessments of direct disposal of spent nuclear fuel in Europe and North America

The Japanese geological disposal programme has started researching disposal of spent nuclear fuel (SF) in deep geological strata (hereafter “direct disposal of SF”) as an alternative management option other than reprocessing followed by vitrification and deep geological disposal of high-level radioactive waste (HLW). In the case of direct disposal of SF, the radioactivity of the waste is higher and the potential effects of the radiation are greater. Specific examples of the possible effects of radiation include: increased amounts of canister corrosion; generation of oxidizing chemical species in conjunction with radiation degradation of groundwater and accompanying oxidation of reducing groundwater; and increase in the dissolution rate and the solubility of SF. Therefore, the influences of radiation, which are not expected to be significant in the case of geological disposal of vitrified waste, must be considered in safety assessments for direct disposal of SF. Focusing especially on the effects of α-radiation in safety assessment, this study has reviewed safety assessments in countries other than Japan that are planning direct disposal of SF. The review has identified issues relevant to safety assessment for the direct disposal of SF in Japan.