Sohei Sukenaga

Capacitance measurement of molten calcium silicate under shear stress field

Abstract The effect of shear stress on the crystallization behavior of molten 50CaO-50SiO2 (mol%) slag was investigated by in-situ measurements of its electrical capacitance in wide temperature range including supercooled region. It is well known that the electrical capacitance of liquids should be generally much higher than that of solids because of the differences in their respective polarization mechanisms. The difference was employed as a sensitive indicator of the crystallization of molten silicates in an experimental furnace equipped with an electrical-capacitance measurement system. The system comprised a Pt-based alloy crucible and a rotating rod that allow us to evaluate the effect of shear stress, both connected to a capacitance meter (LCR meter). As expected, at a particular temperature, the electrical capacitance of the molten calcium silicate abruptly decreased by roughly three orders of magnitude, which clearly indicated crystallization confirmed by corresponding microstructural analyses. It was also found that, for the rotating-rod measurements (with shear stress), the temperatures at which the capacitance abruptly dropped were higher than that without the shear stress. This suggests that the agitation effect by the rotating-rod accelerates the crystallization of molten calcium silicate.

Viscosity Estimation of Spherical Particles Dispersed Suspension

The viscosity measurement has been made for suspensions consisting of polyethylene beads and silicone oil matrix as a function of mean diameter of beads and shear rate. The relative viscosity is found to increase with increasing the volume fraction of beads and decrease with the mean diameter of beads and shear rate. We also tested several viscosity equations to reproduce the viscosity values of spherical particle dispersed suspension. However, any equation could not reproduce well the experimental viscosity values of suspension measured under various conditions. Some modification is needed by considering some experimental conditions (volume fraction, mean diameter of beads and shear rate). Then, the modified Einstein–Roscoe equation is recommended for reproducing the viscosity values of suspension under various conditions.

Phase Separation Behavior and Coloring of Coating Glasses for Sanitary Ware

We investigated the phase separation behavior of multi-component oxide glasses for coating layer of sanitary wares, and the holding time dependence of the microstructure and the coloring nature of phase separated glasses. Two kinds of multi-component silicate glasses (CaO-SiO2-Al2O3-MgO-ZnO-K2O-Na2O system) were employed, which had different CaO/SiO2 ratio. Glass A has higher CaO/SiO2 ratio, and glass B has lower CaO/SiO2. Quenched glasses that were pre-melted at 1550 °C for 90 min in advance, were isothermally held at 800~1100 °C for 0.5~2 h by the hot-thermocouple. The microstructure of phase-separated glass was observed by using FE-SEM on the polished section. It was found that the glass A and B heat-treated at given temperatures indicated a spinodal and a binodal type phase separation, respectively. Moreover, the glass A was found to have the larger microstructure of phase separation, which caused whitish color. In contrast, the glass B revealed the finer binodal phase separation that resulted in a bluish phase separated glass.

Viscosity measurement of molten RE-Mg-Si-O-N (RE=Y, Gd, Nd and La) glasses

Viscosities of molten RE-Mg-Si-O-N (RE=Y, Gd, Nd and La) glasses have been measured using rotating bob viscometer with a gas tight furnace at elevated temperature (~1873 K). Moreover, structural characterizations of these quenched vitreous samples have been investigated using solid state 29Si MAS-NMR, which would resolve the relationship between the viscosity of high temperature melts and network structure of RE-Mg-Si-O-N systems. The viscosities of molten RE-Mg-Si-O-N glasses exponentially increased with nitrogen content. 29Si MAS-NMR spectra of RE-Mg-Si-O-N (RE=Y and La) glasses revealed that content of silicon-oxynitride species, like SiO3N, increased with nitrogen content, which indicates that nitrogen clearly modifies the glass network structure. Depending on cationic radius of rare-earth elements, Y was found to be more effective in silicon-oxynitride species formation than La, which are consistent with the results of viscosity measurement of molten RE-Mg-Si-O-N glasses at elevated temperature (~1873 K).