Yoshinori Akamatsu

Glass Formation of High-Tc Compound BiCaSrCu2Ox by Rapid Quenching

A new high Tc compound, BiCaSrCu2Ox, was successfully prepared in glassy form by a twin-roller quenching method for the first time. The rapidly quenched glass has a glass transition temperature of 390°C and a crystallization temperature (Tx) of 444°C. Heat-treatment at higher temperatures above Tx increased the crystallinity and at 850°C produced X-ray patterns identical to those of the starting compound. The resistivity of the sample heat-treated at 850°C shows the onset Tc at 88 K. These findings are expected to facilitate fiber drawing for such high Tc compounds.

Water-repellent coating films on glass prepared from hydrolysis and polycondensation reactions of fluoroalkyltrialkoxylsilane

Water-repellent glasses for automotive windows are new glass products in which several kinds of fluoroalkylsilanes are used to modify the surface properties of the glass substrates. We examined the hydrolysis and polycondensation reactions of a fluoroalkyltrimethoxysilane (FAS), CF3(CF2)7CH2CH2Si(OCH3)3, by using gas chromatography, gel permeation chromatography and time-of-flight mass spectroscopy. Dimers, trimers and higher polymerized species of FAS were formed by dehydrating the water-repellent coating solutions after a hydrolysis process. The polymerized species of FAS are preferable for improvement of the durability of the water-repellent glasses. However, the excess polycondensation of FAS deteriorates the abrasion resistance, because of the decrease in the number of silanol groups, which are bound to the glass surface. Therefore, appropriate amounts of the polymerized species of FAS play an important role in improving both the abrasion resistance and the UV-light resistance of the water-repellent glasses. The water-repellent glasses obtained from the dehydrated water-repellent coating solution thus show higher durability than those obtained from the non-dehydrated one.

Crystallization kinetics for quenched Bi‐Ca‐Sr‐Cu‐O glasses

The kinetics of crystallization in the BixCaSrCu2Ow (x=1.5, 2.7) glasses prepared by twin‐roller and metal‐plate quenching methods have been studied by a nonisothermal method using differential scanning calorimetry. Scanning electron microscopy studies suggest surface crystallization as the dominant mechanism. The activation energy for crystal growth calculated from modified Kissinger plots assuming surface nucleation decreased with an increase in the Bi content. Such a composition dependence is consistent with that of the activation energy for viscous flow in the glass transformation range.

Instantaneous preparation of superconducting thick films through melts in the Bi-Ca-Sr-Cu-O system

Thick films of Bi-Ca-Sr-Cu-O superconductors were instantaneously prepared by crystallization through melts on a MgO single-crystal substrate. It took only half an hour in annealing to obtain superconducting thick films with Tc (zero) of 93 K and Tc (onset) of 98 K. From the X-ray diffraction patterns of these films, it was found that the superconducting phase was strongly oriented along the c-axis perpendicular to the substrate.

Transition range viscosity of rapidly quenched Bi-Ca-Sr-Cu-O glasses

As a precursor of high Tc superconductors, glasses in the system BixCaSrCu2Ow (x=1.5,2.7) have been prepared using twin‐roller and metal‐plate quenching procedures. Transition range viscosities have been measured on samples as thin as 0.02 mm using the beam‐bending method with a technical modification. From the viscosity data, the system Bi‐Ca‐Sr‐Cu‐O can be characterized as a ‘‘fragile’’ liquid like the ZrF4‐based fluorides. The possibility of drawing fibers of high Tc superconductor precursors is discussed on the basis of the temperature dependence of viscosity.

Ionic conductivity of ZrF4BaF2MX (M = Li, Na;X = F, Cl) glasses

Abstract Glasses were prepared in a wide range of compositions for the two systems oof mixed-cation, ZrF4BaF2LiFNaF, and mixed-anion, ZrF4BaF2LiFLiCl. Ionic conductivities were measured for these glasses and it was found that these glasses were not only cationic but also anionic conductors depending on the total alkali halide content. Four types of mixed-cation and mixed-anion effects on ionic conductivity were demonstrated for the cation-conducting and anion-conducting glasses. In cation conduction, the cation mixing caused the conductivity decline, whereas the anion mixing led to the conductivity enhancement. In anion conduction, on the other hand, the cation mixing led to the conductivity enhancement, whereas the anion mixing caused the conductivity decline.

Large Size Recyclable Colored Glass Plates Prepared from Organic Colorant Dispersed Silica Sols by the Dipping Method

We have prepared the recyclable colored glass plates of blue, green, or red by coating organic colorant dispersed silica sols. Phthalocyanine-type or diketopyrrolopyrrole-type compounds were used as colorants for colored coating and the sol coated glass plates were heat-treated at 300–400°C. The coating was done by using a dipping-withdrawing equipment designed originally for coating large sized glass plates with 2 m in length and 1 m in width. The colored coating films were uniform and transparent with low haze values less than 1.0% and with thickness of 120–540 nm. The visible light transmittance of the colored glass plates was controlled in the relatively wide range of 50–90% by changing the film thickness or the colorant concentration in the coating sols. The practical durabilities of the blue colored glass plate against abrasion, scratch, chemicals and UV-light were acceptable to the specification required for interior glass products.

Substitution Effects of Pb for Bi on the Formation of High-Tc Superconducting Thick Films in the Bi-Pb-Ca-Sr-Cu-O System by the Melt-Solidification Method

Superconducting thick films of Bi1.8Pb0.2Ca2Sr2Cu3Ox have been prepared by the melt-solidification process. The mixtures of oxides or carbonates of each metal were melted on MgO single-crystal substrates at 1000°C for 5 min and then held for crystallization at various temperatures and for various periods. The holding at 850°C for 15 h produced thick films with Tc(zero) at 102 K owing to the deposition of the 110 K phase along with the 80 K phase, both phases being highly c-axis orientated. This is indicative of the effectiveness of the substitution of Pb for a part of Bi for the deposition of the 110 K phase in the melt-solidification process.

Viscosity and crystallization of quenched Bi-Ca-Sr-Cu-O glasses as high-Tc superconductor precursors

Abstract The possible procedure for the fabrication of high- T c superconductor glass-ceramic fibers is proposed on the ground of the transition-range viscosity studies of the Bi-Ca-Sr-Cu-O glasses. The possibility of fiber drawing in the glasses is discussed on the basis of the composition dependence of viscous and thermal properties of the glasses.