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.
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.
The effect of shear stress on the crystallization behavior of molten 50CaO50SiO 2 (mol%) slag was investi gated by insitu measurements of its electrical capaci tance 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 polar ization 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 Ptbased 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 elec trical capacitance of the molten calcium silicate abruptly decreased by roughly three orders of magnitude, which clearly indicated crystallization confirmed by correspond ing microstructural analyses. It was also found that, for the rotatingrod measurements (with shear stress), the temperatures at which the capacitance abruptly dropped were higher than that without the shear stress. This sug gests that the agitation effect by the rotatingrod acceler ates the crystallization of molten calcium silicate.
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