Effect of Agitation on Crystallization Behavior of CaO^|^ndash;SiO2^|^ndash;R2O (R = Li, Na, or K) System Characterized by Electrical Capacitance Measurement

Abstract

The effect of agitation on the crystallization behavior of molten 50CaO-50SiO2 and 45CaO-45SiO2-10R2O (R = Li, Na, or K, mol%) fluxes were systematically investigated by the measurement of their electrical capacitance over a wide temperature range from liquid region to well below the liquidus temperature. It is well known that the electrical capacitance of liquids is generally much higher than that of solids owing to the differences in their respective polarization mechanisms. These differences were exploited as a sensitive indicator of the crystallization of molten calcium silicates in an experimental furnace equipped with an electrical capacitance measuring system. The system comprised a Pt-based alloy crucible and a rotating rod that allowed evaluation of the effect of agitation generated by the rod, connected to a capacitance meter (LCR meter).As expected, at a particular temperature, the electrical capacitance of the molten calcium silicates underwent a precipitous decrease by roughly three orders of magnitude, which was dependent on the chemical composition. This indicated the presence of crystallization and this was confirmed by corresponding microstructural characterization. It was also found that, for the measurements acquired with rotating rod agitation, the temperatures at which the capacitance underwent the sharp decrease were higher than that identified without the agitation. This suggests that the agitation effect induced by the rotating rod accelerates the crystallization of molten calcium silicates.

Crystallinity of Supercooled Oxide Melts Quantified by Electrical Capacitance Measurements

“…In general, the crystallization of a supercooled oxide melt significantly affects its macroscopic and physical properties, such as viscosity and thermal conductivity of the produced solid phase. For example, the degrees of lubrication and insulation between an oscillating mold and molten steel during continuous casting 16) significantly depend on the viscosity and crystallinity of the molten phase 6,17,18) due to the rapid increase in the amount of dispersed solids. Consequently, the viscosity properties of a melt depend on its shear rate, which can dramatically turn a Newtonian fluid into a non-Newtonian one.…”

Shear Rate and Crystalline Phase Effects on the Super-Cooling Degree and Crystallization Behavior of CaO–SiO₂–CaF₂–RO (R=Mg, or Sr) Flux Systems

“…Therefore, the crystallization temperature increased with respect to the cationic radius (Mg 2 + < Sr 2 + ), which corresponds well with the results of a previous study of the CaO-SiO 2 -R 2 O (R = Li, Na, or K) system. 14) In comparison with the base slag of the CaO-SiO 2 -CaF 2 system (C/ S = 1.2, CaF 2 = 10 mol%), 15) the crystallization temperatures of the slag containing MgO were lower than those of the CaO-SiO 2 -CaF 2 system. In contrast, the crystallization temperatures of the slag containing SrO were higher than those of the CaO-SiO 2 -CaF 2 system.…”

“…8 and 9, its effect was insignificant for the crystallization of the cuspidine phase. In the previous study of the CaO-SiO 2 -R 2 O (R=Li, Na, or K) 14) and CaO-SiO 2 -CaF 2 15) systems, the crystalline phase tended to change from CaO-SiO 2 to dicalcium silicate, or cuspidine, as the cationic radius of the added materials increased. Merwinite is a magnesium substitute of dicalcium silicate, so when merwinite was considered as one of the dicalcium silicates, the tendency of the crystalline phase was similar to that in the present and previous studies.…”

“…Few studies, however, have been conducted where crystallization was investigated during the agitation of the sample. 14,15) The method of electrical capacitance measurements reported by Ohta et al,20) with which it is possible to observe the crystallization of oxide melts in-situ, was utilized in the present work in order to under- stand the effects that agitation had on the crystallization of CaO-SiO 2 -R 2 O (R = Li, Na, or K) 14) and CaO-SiO 2 -CaF 2 15) systems.…”

“…[11][12][13] Especially, the flux's viscosity and thermal conductivity are drastically changed by its solid volume fraction and crystallinity. 4,14,15) Therefore, an understanding of the flux crystallization behavior is important in order to…”