Wettability of Silicon Carbide by CaO-SiO 2 Slags
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INTERFACIAL properties at the solid–liquid interface play an important role in many metallurgical processes. The degree of wetting a solid by a liquid in a solid–liquid–gas, three-phase system is characterized by the conditions of thermodynamic equilibrium. The profile adopted by a liquid drop resting in equilibrium on a flat horizontal surface is governed by the balance between surface and gravitational forces (Figure 1). The relationship between the contact angle and the respective interfacial tensions acting at point A of three-phase contact is given in the Young equation,[1] which is as follows: ðcSG cLS Þ ¼ cLG cos h
½1
where h is the contact angle and cLG, cLS, and cSG are the liquid/gas, liquid/solid, and solid/gas interfacial tensions, respectively. When a reaction occurs at the interface, the free energy change per unit area per unit time also enhances wetting. In this case, the Young equation [1] should be corrected for this driving force. According to Laurent,[2] the smallest contact angle possible in a reactive system is given as follows: cos hmin ¼ cos h0
Dcr DGr cLG cLG
½2
JAFAR SAFARIAN, Researcher, and MERETE TANGSTAD, Professor, are with the Norwegian University of Science and Technology, Alfred Getz Vei 2, 7491, Trondheim, Norway. Contact e-mail: [email protected] and Merete.Tangstad@ material.ntnu.no. Manuscript submitted February 11, 2009. Article published online September 1, 2009. 920—VOLUME 40B, DECEMBER 2009
Here, h0 is the contact angle of the liquid on the substrate in the absence of any reaction. Dcr takes into account the change in interfacial energies brought about by the interfacial reaction, and DGr is the change in free energy per unit area released by the reaction in the immediate vicinity of the liquid/substrate interface. In general, DGr is one of the major factors that governs wetting in the reactive system. However, it is difficult to determine this value quantitatively from experiments or from theoretical calculations. In reality, the difficulty remains in correlating the time-dependent interfacial reaction with the kinetics of wetting. In many metallurgical processes, silicon carbide (SiC) is in contact with molten phases. For instance, more than 65 pct of the industrialized world’s iron blast furnaces use SiC bricks as the lining materials.[3] Silicon carbide also has contact with molten aluminum and cryolite in electrolytic reduction cells for the production of aluminum, in which SiC is used as the sidewall lining.[4] In the directional solidification of silicon, which is used to produce silicon feedstock for solar cells, when carbon exceeds its solubility limit in silicon, SiC particles are produced and dispersed throughout the melt.[5] In the present study, the contact between silicon carbide and CaO-SiO2 melts is investigated. The surface tension of CaO-SiO2 slags has been measured in several studies. The dependence of slag surface tension on the temperature is small.[6–10] For instance, on the one hand, the surface tension of a slag with 0.
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