A New Experimental Design to Study the Kinetics of Solid Dissolution into Liquids at Elevated Temperature
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THE rotating disk/cylinder (rod) method has been widely applied to study the dissolution of solids in liquids for decades,[1–20] in particular for high-temperature systems such as dissolution of solid metals into liquid metals, and dissolution of ceramic solids into liquid oxides (slags). While valuable information have been gained by these studies, some misconceptions in using this method need to be addressed and analyzed. This is especially true when a cylinder and a small crucible are used. A number of researchers have studied the dissolution rate by rotating a rod concentrically placed in liquid in a small crucible. For example, Matsushima et al.[12] studied the dissolution of solid CaO into liquid slag by using a rotating rod method. A so-called J-factor was introduced to express mass transfer in the liquid. Umakoshi et al.[7] also used this method to investigate the dissolution rate of burnt dolomite in converter slag. They reported that the dissolution rate was not affected by the porosity of the sample. Choi et al.[10] investigated the dissolution of
HUIJUN WANG, JESSE F. WHITE, and DU SICHEN are with the Department of Materials Science and Engineering, Royal Institute of Technology, SE-10044, Stockholm, Sweden. Contact e-mail: [email protected] Manuscript submitted 13 July, 2017. Article published online February 9, 2018. 688—VOLUME 49B, APRIL 2018
Al2O3 in the CaO-SiO2-Al2O3 slag system. The torque of the rotating alumina rod dipped into liquid slag was found to be related to the dissolution rate. In fact, the limited applicability of this rotating cylinder method was pointed out clearly by Gregory and Riddiford.[21] They emphasized that this method was only applicable to a disk rotating in a vessel considered to be infinitely large. They also stated that the rotating disk should have a very large ratio between the diameter and thickness. Cooper and Kingery pointed out that the position of the rotating disk played an important role in the dissolution.[1] The constraints of the rotating disk method emphasized by those authors were confirmed in a previous study.[22] Here, the authors reported that the method of a rotating rod in a crucible was unsuitable for the study of dissolution phenomena. CFD calculations were employed to evaluate the velocity distribution of the liquid flow when a rod is rotated concentrically in liquid in a small container. It was found that mass transfer in the liquid could not be enhanced by forced convection since no radial flow would be generated by the rotation of the concentrically placed long rod. Moreover, the dissolution rate of a cylinder in a liquid greatly depends greatly on the nature of the experimental setup.[22] For example, the cylinder usually is attached to a very long shaft in a high-temperature experiment. When high-speed rotation is employed, the long shaft along with the cylinder is very difficult to be kept exactly in the center of the container. A METALLURGICAL AND MATERIALS TRANSACTIONS B
non-concentric placement would affect the dissolution results, (system depe
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