Catalytic graphitization of Glassy Carbon by Molten Fe-C sat
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Long blast furnace (BF) campaign lives (of greater than 20 years) rely on careful choice of the carbon refractory materials that are used to construct the blast furnace hearth.[1] A common design philosophy is to ensure that the hot-face temperature of the refractory is below 1150 °C (the eutectic temperature in the ironcarbon system), to ensure solidification of a protective iron-carbon skull between the refractory and the liquid hot metal.[1] Low hot-face temperatures are achieved by cooling the hearth wall and using higher-conductivity, graphitic carbonaceous refractory.[2] However, some wall wear does occur, particularly in areas of higher flow rate near tap holes, where the elevated heat transfer rate can cause temporary loss of the solidified skull during tapping. While the rate at which the exposed carbon dissolves into undersaturated hot metal is often assumed to be under liquid-phase mass transfer control[3], the structure of the carbonaceous refractory is also considered to affect its dissolution rate: graphitic material is generally not used at the hot face because of its higher dissolution rate in molten iron than lesscrystalline materials such as semigraphitized carbon.[2]
THOMAS BRITT and PETRUS CHRISTIAAN PISTORIUS are with the Department of Materials Science and Engineering, Center for Iron and Steelmaking Research (CISR), Carnegie Mellon University, Pittsburgh, PA 15213. Contact e-mail: [email protected] Manuscript submitted July 27, 2020 and accepted October 8, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS B
An effect of the crystallinity of coals and graphite on their dissolution rate in liquid iron was reported[4], though differences in mineral and sulfur content (of the carbonaceous material) strongly affect dissolution rates.[5,6] Given the possibly confounding effect of inorganic material when studying the dissolution of less-crystalline carbons, glassy carbon (vitreous carbon) is a potentially interesting material. Glassy carbon would not be practical as a large-scale refractory lining (given its high cost, low fracture toughness, and low thermal conductivity). However, its high purity and less-crystalline structure would be expected to affect its dissolution behavior, and so could serve to test the proposed link between crystallinity and dissolution. The density of glassy carbon is approximately 35% lower than that of graphite.[7] While most of the bonds in glassy carbon are sp2 (as in graphite), glassy carbon is thought to be comprised of small, single graphite-like sheets which entangle due to curvature from non-6 member rings.[8,9] The structural difference results in a higher Gibbs free energy of carbon in glassy carbon than in graphite, causing higher solubility of glassy carbon than graphite in liquid nickel.[10] The solubility difference was found to cause destruction of glassy carbon in contact with various liquid metals[11]: the glassy carbon dissolved in the liquid metal, and then reprecipitated as graphite (in a process termed ‘‘catalytic graphitization’’). In addition to constraints imp
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