Manabu Koide

Viscosity of fluoride glasses at glass transition temperature

Abstract The viscosities of some fluoride glasses were measured by the penetration method in the glass transition temperature range, and the glass transition temperature was determined from DSC as a function of the heating rate. It was concluded that the viscosity at the glass transition temperature increases as the heating rate decreases, approaching 1012 Pa s at zero heating rate for all fluoride glasses.

Viscous flow mechanism of fluoride glasses over a wide temperature range

Abstract The viscosities of fluoride glass melts were measured by a penetration method in the low temperature range and by rotational method in the high temperature range. It was found that the low temperature viscosity changes extraordinarily with temperature and the high temperature viscosity changes very slightly with temperature. The measured viscosity over a wide temperature range was found to be fitted very well to the following equation which was derived by modifying the Macedo-Litovitz equation, log η = A + B/Tn + C/(T − T0), where A, B, C, T0 and n are constants. The quantity nB/Tn−1 is assumed to correspond to the activation energy for the flow unit to jump from a site to the adjacent site. These results were compared with silicate glass melts and it was estimated that the flow unit size in fluoride glass melts is very large at the glass transition temperature region and becomes smaller as the temperature increases.

Low-temperature deformation of fluoride and oxide glass fibers below their glass transition temperatures

Abstract Deformation of some fluoride and oxide glass fibers were measured at temperatures below their glass transition temperatures. Glass fibers were wound on a cylinder, kept at low temperatures for various times and the remaining strains of fibers after the heat treatment were measured. It was found that the temperature region in which fluoride glass fibers are deformed is much lower than that for oxide glass fibers. The deformation mechanisms of each of the glass fibers were analyzed based on a log-normal distribution model of relaxation times. It was found that the activation energy for low-temperature deformation is much lower than that for viscous flow near the glass transition temperature. It was concluded that the deformations of each of the glass fibers are caused by different relaxation mechanisms.

Viscous flow mechanism of oxyfluoride glasses related to glass structure

Abstract The viscosities of 30PO · (70-x)SnF2 · xSnO glasses were measured over a wide temperature range, and the viscous flow mechanism is compared with those of silicate and fluoride glasses. It was found that the viscosity and activation energy decrease as the concentration of fluoride ions increases. The viscosity can be expressed by the Fulcher equation over a wide temperature range except for the glass of the low fluorine content. Sn2+ ions are thought to play the role of network modifiers and the viscous flow behavior is determined by weak SnF and PF bonds.

Nano-Crystallized Glass Fibers with Second-Order Optical Nonlinearity

Transparent nano-crystallized glass fibers with 300μm diameter were successfully fabricated in tellurite (TeO2) based glass systems. Structure of crystallized glass fibers and orientation of nano-size crystals were quantitatively investigated by microscopic Raman spectroscopy and X-ray diffraction. Second harmonic generation was measured in the nano-crystallized optical fibers.

Viscosity and relaxation of glasses below the glass transition temperature

The fiber bending method has been used for the measurement of the viscosity of glasses below the glass transition temperature. It was found that the viscosities of as-drawn and pre-annealed glass fibers below the glass transition temperature increase with increasing pre-annealing temperature and time. It was also found that the viscosity approaches the extrapolated line from the Fulcher curve fitted at temperatures above the glass transition temperature. On the other hand, by analyzing the relaxation mechanism, it was found that the stretching parameter decreases with decreasing temperature, suggesting wider distribution of relaxation time at lower temperature. By extrapolation it was found that the stretching parameter is about 0.6 near the glass transition temperature. This means that at the glass transition temperature the relaxation mechanism consists of more than one mode.

Delayed elasticity and viscosity of silicate glasses below the glass transition temperature

The viscosity of pre-annealed lead-silicate glass was studied below the glass transition temperature using the fiber-bending method. The viscosities were determined under conditions of loading and unloading. The delayed elasticity and its effect on the viscosity were also investigated. In the case of equal loading and unloading times, the viscosity was the same for the loading and unloading processes and the delayed elasticity was larger within shorter periods and smaller for longer ones. In addition, the time necessary for the recovery of the delayed elasticity increases with increasing loading time.