Among the trivalent ion conductor series of Sc2(WO4)3 type and NASICON type that we have reported, the highest ion conductivity was obtained for the trivalent Al3+ ion conducting NASICON type (AlxZr1-x)4/(4-x)Nb(PO4)3 solid electrolyte and the value enters the area between yttria stabilized zirconia (YSZ) and calcia stabilized zirconia (CSZ) of well known commercialized high oxide anion conductors. The enhancement of both the ion conductivity and the mechanical strength was simultaneously realized by adding B2O3 as a sintering agent during the sintering procedure. The Al3+ ion conducting (AlxZr1-x)4/(4-x)Nb(PO4)3 solid electrolyte with the B2O3 additive was combined with YSZ, and the refractory oxide based solid was set on the (AlxZr1-x)4/(4-x)Nb(PO4)3 solid surface as the individual auxiliary electrode for carbon dioxide (CO2), nitrogen oxides (NOX), sulfur dioxide (SO2) gas sensing, respectively. The sensor response was rapid, reproducible and continuous with obeying the Nernst theoretical relationship.
Silicon nitride ceramics were fabricated by dry pressing of a raw α-Si3N4 powder with Y2O3-SiO2 and Y2O3-Al2O3 as sintering aids, following by gas-pressured sintering at a temperature of 2123 K for 2 h under a nitrogen gas pressure of 1.0 MPa with Si3N4/BN packing powder. Subsequently, these specimens were heat-treated at a temperature up to 2223 K for 8 h under a nitrogen gas pressure of 1.0 MPa without any packing powder. Mass loss, density, oxygen content and thermal conductivity of the specimens before and after the post-sintering heat-treatment were measured. Due to the heat-treatment, the reduction of oxygen content, via the reaction of Si3N4 and SiO2, without decrease of relative density was found to be effective in improving thermal conductivity of the Si3N4 ceramics sintered with Y2O3-SiO2 additives. The effect of post-sintering heat-treatment was not significant for the Si3N4 specimen sintered with Y2O3-Al2O3 additives due to formation of SiAlON. Thermal conductivity of one of the former specimens reached 84 W/m•K at room temperature.
Incorporation of Ni ions into two different sites of the Na and Co sites of NaCo2O4 was carried out by the processes of conventional elemental substitution for Co ion and solid state ion exchange of mobile Na+ ion. The changes of the lattice parameters of “substituted” and “exchanged” samples were different, suggesting that the Ni ions occupy different sites. The Ni-substituted sample for Co showed a significant decrease of Seebeck coefficient keeping the electrical conductivity almost intact, while Ni-exchanged samples for Na showed a lower electrical conductivity than that of the non-substituted sample with keeping the Seebeck coefficient unchanged. These results suggest that Ni cations introduced to the Co site decouples the Co-Co spin exchange, whereas those at the Na site compensates positive holes by providing conduction electrons.
In order to elucidate the wear mechanism of direct-bonded magnesia-chrome ore refractories in RH-TOB (RH-Top Oxygen Blowing), crucibles were made from the MgO-Cr2O3 refractory, which are used as a side wall refractory material for the RH-TOB lower vessels. The crucibles were charged with melting stock to carry out the oxygen blowing experimental at 1650°C. Experiment was discriminated the wear by FeO permeation and the wear by Fe fume. The chromite in the MgO-Cr2O3 refractory creates a complex spinel of a high melting point with FeO, therefore chromite is stable and shows a high corrosion resistance on FeO. On the other hand, FeO that has a very low melting point permeates magnesia that are composed of fine particles combined by silicate bonds. Consequently, an eutectic reaction causes the bond melts and separating the particles. The wear during the RH-TOB process results from the oxidation heat that is produced when the Fe fumes react with oxygen and impact the refractory dissolve away both magnesia and chromite.
A novel joining technique of ceramics to metals is presented, in which depositing Ti on ceramics with arc-added glow discharge is used as a prior metallizing technique and then brazing the ceramics to metals by abnormal glow discharge is carried out. The heating temperature of the base metals is easily controlled by varying the operating voltage and barometric pressure. The ions beam from the glow discharge anode is efficiently able to sputter-clean the surfaces of the base materials, which thereby improves better Ti-deposited adhesion on the ceramics and the wetting and spreading properties of the filler metal. The thickness of the Ti-deposited layer is readily adjusted in terms of the actual requirement. The vacuum pressure during brazing can be up to 5 Pa. The cost and duration of the glow discharge plasma brazing are reduced as compared with the traditional vacuum brazing process. The joining technique developed holds potential for industrial applications leading to high product quality.
The purpose of this study was to elucidate the effect of body and glaze composition on the mechanical properties of porcelain strengthened by addition of 15 mass% of α-alumina fine powder and by crystallization of cristobalite. With the increase in amount of cristobalite, thermal expansion coefficient of bodies increased. Precise control of cristobalite content in a body proper for glaze to generate compressive stress of 90 MPa improved the bending strength of porcelain from 160 MPa up to 230 MPa. Excess compressive stress in glaze induced by much difference in thermal expansion coefficient had to be avoided, because it led to shivering in glaze and body. Stress and strain in glaze were calculated, and the fracture mechanism was theoretically considered from the viewpoint of a fracture criterion taking into account fracture origins and mechanical properties.
Nanocrystallized glasses with the composition of 40BaO•20TiO2•40SiO2, stoichiometric to fresnoite (Ba2TiSi2O8), have been prepared by heat-treatment at various temperatures, and their optical properties, second-harmonic generation (SHG) and photoluminescence (PL), have been examined. The glass subjected to the heat-treatment at 760°C for 1 h showed a dense formation of Ba2TiSi2O8 crystals with the dimension of 200-300 nm, and maintained a visual transparency. Visible green light corresponding to SHG at 532 nm was confirmed in the transparent Ba2TiSi2O8 nanocrystallized glasses. The maximum second-harmonic intensity in the nanocrystallized samples was on the order of 1/100 when compared to that of an α-quartz single crystal. Furthermore, the bluish white PL with a peak at the wavelength of about 470 nm was also visually observed in samples heat-treated at 750-800°C.
We have succeeded in the synthesis of a thermostable zeolite with a novel framework structure (CDS-1: Cylindrically Double Saw-edged zeolite; CDO topology) from a novel layered silicate (PLS-1: Pentagonal-cylinder Layered Structure) by topotactic dehydration-condensation between pure silicate layers consisting of face sharing of pentagon cylinders. The purely siliceous zeolite CDS-1 has a chemically inert silicate framework and consequently no acid sites. In order to expand the catalytic potential of CDS-1, incorporation of various metals into the zeolite framework is necessary. In this study, we tried to prepare the Al containing CDS-1 zeolite (Al-CDS-1) by (1) alumination of CDS-1 zeolite and (2) transformation of Al-PLS-1. The catalytic performance was also evaluated by a few test reactions such as 1-hexene and cumene cracking and dehydration of 2-propanol.
The objective of this study was to form a polycrystalline oxide film on Al substrate using micro-arc-technology. According to the kind of electrolytic solution used micro-arc-processing was either possible or not. A crystallized Al2O3 film on the Al substrate was formed by micro-arc-processing in a NaOH electrolytic solution. But the discharge dispersion happened due to the condition of pretreatment on the Al substrate. This discharge dispersion did not occur in the mixed electrolytic solution of NaOH and Na2SiO3, and a crystallized Al2O3 film was formed on the Al substrate when it stabilized. In addition, the film had a bilayer structure with the under-layer near the Al substrates made of the high-density principal component γ-Al2O3 and α-Al2O3. The upper layer was made of γ-Al2O3 in the porous phase.
Silica pillared clays with large interlayer distance were synthesized by the simultaneous intercalation of 3-aminopropyltriethoxysilane (APS) and polyvinyl alcohol (PVA). Characterization of the synthetic silica pillared clay was done by X-ray diffraction measurement, nitrogen adsorption-desorption measurement and X-ray fluorescence analysis. The gallery height of the synthesized pillared clay was 1.3 nm in the presence of PVA, and it was found that the gallery height was twice as large as that of the pillared clay synthesized without using PVA. The specific surface area and pore volume of the pillared clay obtained with PVA were larger than those obtained without PVA. It was confirmed that the interlayer distance was enlarged with increase in the amount of pillaring precursors only by using PVA.
Zinc oxide particles were prepared by heating zinc hydroxide precipitate in a mixed solution of H2O and ethanol at 348 K for 2 h. When the molar fraction of ethanol in the solution increased, the particle size of the obtained zinc oxide decreased. The band-gap absorption edge of the UV-VIS spectra of the obtained zinc oxide particles also shifted to the shorter wave length with an increase of ethanol molar fraction in the mixed solution. When zinc hydroxide was heated in pure ethanol, zinc oxide nanoparticles whose average diameter was 41 nm were obtained. The zinc oxide nanoparticles can be obtained by heat treatment of zinc hydroxide in the neutral solution at 348 K.
The silica sand is primarily composed of high purity SiO2. Mt. Iide over Niigata, Yamagata and Fukushima prefectures is known as a rich mine for silica sand. In this study, we adopted natural resource (silica sand from Mt. Iide, Osodani area) as a starting material for the synthesis of akermanite type long-persistent phosphor Sr2MgSi2O7: Eu2+, Dy3+. The silica sand derived (Sr0.98Eu0.01Dy0.01)2MgSi2O7 showed long afterglow phenomena. Therefore, the silica sand can be potentially used in preparing silicate phosphors.
Firing is one of the most important processes for trial-producing art porcelain. There are two disadvantages of shuttle kiln for firing art porcelain. The first is that it is difficult to repeat the firing process of the best art effect porcelain that appears by a chance. The second is that the only one firing process can be carried out in the kiln at one time. In order to solve those problems, the trial kiln for firing art porcelain was designed. The designed trial kiln has remained the characteristics of traditional shuttle kiln, but the whole room of the kiln can be divided two kiln rooms (the front and back rooms) by clapboard. And two independent control systems were designed in the kiln to control firing temperature, pressure and atmosphere system in the front and back rooms, respectively. When the clapboard is removed, the two systems can form one system to control the whole kiln. The results of firing celadon in the trial kiln indicate that not only firing process can be auto controlled and repeated very well but also two kinds of products can be fired with different firing processes in the kiln at the same time. Iron ion content of the different chemical valence in the glaze was analyzed with Mössbauer spectroscope. The results indicate that the different reducing atmosphere and fire curve can be controlled in front and back kiln rooms in the trial kiln, respectively, and its repeatability is very good.