Reactions Between Liquid CaO-SiO 2 Slags and Graphite Substrates
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GRAPHITE is an exceptional refractory material that is used extensively in the smelting, melting, refining, and crystallization of silicon as well as in other metallurgical systems where carbon solubility is limited. Besides unsurpassed refractoriness, at low oxygen potential, graphite is chemically stable and has high resistance to thermal shock. Graphite also has the added benefit of being a soft material that is easily machinable to almost any shape or form. In actuality, commercially available synthetic graphites are not simple materials—there are a panoply of graphite grades on the market from numerous suppliers, and the manufacturing processes and production recipes can be quite diverse. As such, the thermophysical properties as well as the chemical reactivity of these different graphite grades can widely vary. Several published studies investigated the wetting of carbonaceous substrates with slags; all of these studies employed high-temperature sessile drop apparatuses to measure the change in apparent contact angle of a molten slag droplet on a substrate over time, with several employing scanning electron microscopy (SEM) to analyze the reaction interfaces.[1–10] Most studies were in the context of ironmaking processes, and thus, they involved iron-bearing slags reacting and spreading on coal char, coke, and both natural and synthetic graphite substrates.[1–8] The reduction reaction of FeO by the JESSE F. WHITE, Research Scientist, JAEWOO LEE, Postdoctoral Research Associate, OSCAR HESSLING, Graduate Student, and BJOERN GLASER, Assistant Professor, are with the Department of Materials Science and Engineering, KTH Royal Institute of Technology, SE-100 44 Stockholm, Sweden. Contact e-mail: jfwhite@ kth.se Manuscript submitted June 23, 2016. Article published online September 26, 2016. 506—VOLUME 48B, FEBRUARY 2017
carbon substrate has been found to play a major role in the wetting behavior in such systems.[3,4] Some studies focused specifically on the wetting behavior of nonferrous slags: Recently, Oh and Lee measured the wetting of CaO-SiO2-Al2O3-MgO slags on pressed coke substrates at 1773 K (1500 C); they attributed the process of slag wetting to the formation of SiC at the slag–graphite interface.[9] Heo, Lee, and Chung made similar measurements of the wetting of CaO-SiO2(-Al2O3) slags on MgO-C and graphite substrates at 1873 K (1600 C).[10] Some studies made careful analyses of the kinetics of slag–graphite reactions, including measurements of the concentration of CO and CO2 gas in the furnace off-gas using a mass spectrometer, and the change in slag composition with time.[4,7,8] Liquid slags react with carbon in surprisingly complex ways. The reduction of silica in the slag and the adverse effect of increasing slag basicity (decreasing silica activity) on the spreading of slag has been documented in several of these studies.[1,5,7–9] Gas evolution during wetting of carbonaceous substrates with slag has also been described by several others.[1,3,4,8] Some industrial processes contain both a liquid m
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