Effects of Agitation and Morphology of Primary Crystalline Phase on Crystallization Behavior of CaO–SiO2–CaF2 Supercooled Melts

Abstract

The effects of the agitation field and the crystal morphology on the primary and secondary crystallization temperatures of CaO-SiO 2 -CaF 2 supercooled melts were systematically investigated by measuring the electrical capacitance.Two-stage decreases in electrical capacitance were observed for most samples investigated. These stages correspond to the primary crystallization and the eutectic reaction resulting from the compositional change in the supercooled melts associated with the primary crystallization, respectively.The primary crystallization of dendritic CaO·SiO 2 was affected by the agitation in the same manner as reported previously, but the crystallization of faceted 3CaO·2SiO 2 ·CaF 2 revealed little dependence on the agitation. This indicates that the effects of the agitation are different for different morphologies of the primary crystalline phase because of shifts in the rate-determining step of crystallization.

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.…”

“…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.…”

“…Recent studies have suggested that there is a change in the crystallization temperature and crystalline phase as a function of shear rate. 15) With the purpose of improving the iron and steel making processes, a systematic investigation of crystallization and super-cooling of CaO-SiO 2 -CaF 2 -MgO slag under simulated actual operating compositions and conditions was performed. As part of this investigation, MgO was replaced with SrO since it is a similar alkaline earth metal oxide and may have a significant impact on the development of iron and steel fabrication processes.…”

“…[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…”