Nobuyuki Takeuchi

Investigations of the electrical property, diffuse reflectance and ESR spectra of the La-(Fe, Mn)-codoped PTCR BaTiO3 annealed in reducing atmosphere

Electrical properties of La-(Fe,Mn)-codoped positive temperature coefficient of resistivity (PTCR) BaTiO3 ceramics were studied by combining their diffuse reflectance measurements and electron spin resonance (ESR) spectroscopy. La-(Fe,Mn)-codoped samples showed high durability to reducing atmosphere. It is assumed that Fe and Mn ions segregated in the grain boundary contribute to the density of surface acceptor states, meanwhile localizing electrons in a form of Ti3+ and stabilizing the chemisorbed oxygens through La3+-Mn3+,4+ or La3+-Fe3+ pairs. In addition, ESR signals of Fe3+ in annealed samples was intensified above Curie temperature (Tc), indicating that Fe ions still maintained its high valence states (Fe3+) in the grain boundary even after annealing in reducing atmosphere.

Mineralizing action of iron in amorphous silica

Abstract The mineralizing action of iron in amorphous silica was investigated by firing mixtures of silica gel and iron oxides at 1100 and 1150°C. Silica gel did not crystallize in the absence of ferrous ion below 1200°C. When silica gel mixed with ferrous oxalate was heated at 1100°C in a mildly reducing atmosphere(N2, CO2, CO), quartz, cristobalite and ferrous silicate (Fe2SiO4) were formed. Application of the reducing atmosphere from room temperature promoted the crystallization to quartz, while that from the soaking temperature after heating in N2 accelerated the formation of cristobalite. Chemical analysis revealed that the N2 atmosphere acted as a mildly oxidizing atmosphere to FeO possibly due to the coexistence of water vapor released from silica gel and impurity O2. Furthermore, tentative crystallization mechanism is proposed where mildly reduced and mildly oxidized Fe2SiO4 produced nuclei for quartz and cristobalite, respectively.

Effect of heating and cooling atmospheres on colors of glaze and glass containing copper

Abstract ESR and ESCA analyses of a copper red glaze prepared by firing under a strongly reducing atmosphere followed by oxidation during a cooling period showed that Cu 1+ and Cu 2 O were major species in it. From the investigation of behavior and chemical states of copper and tin under various firing conditions, mechanisms of the formation of Cu 2 O and its protection were assumed as follows: Cu 2+ and Sn 4+ are reduced to metals during reducing firing and then the metals aggregate in the glaze surface layer, forming alloy. In the next oxidation process, metallic copper and tin are oxidized to Cu 2 O or Cu 1+ and SnO respectively. Due to the affinity of SnO on Cu 2 O for glass, glass containing Sn 2+ surrounds and consequently protects Cu 2 O from excessive oxidation. A colorless copper glass before striking contained copper mainly as Cu 1+ . ESCA analysis showed that striking of the glass caused the selective formation of Cu 2 O.

Conversion of silica gel and silica glass mixed with various metal oxides into quartz

Mixtures of silica gel and various metal oxides were heated at temperatures within the range of 500 to 1200°C for 1 h. When mixtures of silica gel and intentional additives such as Li 2 CO 3 , MgO, CaCO 3 , SrO, Ba(CH 3 COO) 2 , and ZnO were heated at temperatures from 700 to 1050°C, quartz phases formed. Similarly, heating a mixture of powdered silica glass and Li 2 CO 3 yielded quartz. In all cases the formation of quartz phases always accompanied the formation of silicate minerals. When a mixture of silica gel and 1 wt% Li 2 CO 3 was heated at 900°C, quartz phases and a very small amount of Li 2 Si 2 O 5 (hereafter denoted as Q-S mixture) were formed. Silica gel mixed with 10 wt% of Q-S mixture was transformed almost completely into quartz phases at 1000°C. The Q-S mixture consisted of only quartz phases after washing with hot H 2 SO 4 . Silica gel mixed with 10 wt% of the washed Q-S mixture was not transformed into quartz, but rather into cristobalite above 1200°C. This fact also indicates that the formation of the silicate mineral is a necessary precursor to the conversion of silica gel and silica glass into quartz.

Effect of furnace atmosphere on color of iron glaze

The glaze containing 1.8wt% Fe 2 O 3 were invariably yellow when fired under oxidizing and neutral atmospheres, but showed a wide range of color when fired under reducing atmosphere depending on the concentration of reducing gases and cooling conditions. From chemical analysis, it was found that the glazes fired in air and nitrogen contained iron mostly in a state of Fe 3+ and that those fired under reducing atmosphere contain major part of Fe 2+ and a small amount of Fe 3+ . The ESR signals of Fe 3+ and metallic iron were not observed in the greenish blue glaze. This result suggested that the greenish blue color was produced by Fe 2+ associated with a small amount of Fe 3+ . The X-ray diffraction analysis showed the presence of metallic iron in the black glaze fired under strong reducing atmosphere. From the EPMA results that iron was highly enriched in the surface layer of this black glaze it was assumed that iron aggregated into metal during firing.

Role of Sn2+ in development of red color during reheating of copper glass

It was found that migrations of both Cu 1+ and Sn 2+ in glass occurred above 500 °C. In the case of conventional copper glass containing both Cu 1+ and Sn, Cu 2 O formation during striking takes place dominantly in its interior but in contrast, on reheating the glass in vacuo which did not contain Sn 2+ , Cu 1+ scarcely precipitated in the interior of the glass but aggregated as Cu 2 O on its surface. Thus, the role of Sn 2+ in striking was considered to be the formation of the nucleus on which Cu 1+ could deposit as Cu 2 O. In some cases, metallic copper was detected in the struck glasses by ESCA. These results indicate that metallic copper formed by reduction of Cu 1+ by Sn 2+ acts as the center of deposition for Cu.

DFT Study of Oxygen Reduction Reaction on N-substituted Carbon Electrodes. Adsorption

Carbon alloys attract attention as metal-free cathode catalysts. Mechanisms of oxygen reduction reactions are investigated using the DFT calculations and molecular models such as N-substituted coronene, circum pyrene, and corannulene. The overall oxygen reduction reaction (ORR) is decomposed into five elementary reactions. Adsorption of O2 is important as the first step of reduction, and it depends strongly on the spin density on C atoms, introduced by the N atom. Secondly the peripheral C atoms have an advantage due to the rehybridization freedom to the sp3 configuration. Based on the reversible electrode potential (REP) for each elementary reaction, the overpotential is expected for the first reduction of O2 to OOH and the final reduction of OH to H2O. These features indicate that N-substituted carbon electrode resembles Pt electrode compared to other less active metals, such as Au.

Optimized method of producing washers of titanium hydride for plasma gun using occluded hydrogen gas

An optimized way of producing washers of titanium hydride for the application to a plasma gun using the occluded gas is presented. The amount of H2 gas (equivalently, gas pressure p) is entirely preadjusted in a gas reservoir of a simple instrument. The temperature T of a furnace is completely feedback controlled. Data show that when p is the order of 1atm, T needs to be higher than about 450°C in order to successfully produce washers of titanium hydride. Results on compressive strength of the loaded washers suggest that an appropriate ratio of atoms of hydrogen to titanium is less than H:Ti∼0.85:1.