Effect of Multiwalled Carbon Nanotubes on the Thermal Conductivity and Porosity Characteristics of Blast Furnace Carbon
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ODUCTION
THE life of a blast furnace (BF) is determined mainly by the rate of erosion and corrosion of hearth and bottom carbon refractories.[1,2] Currently, carbon refractories for a BF are being developed with high thermal conductivity (TC) and a highly microporous structure for two reasons: First, high TC can sustain the risk of high thermal loads and large temperature gradients, and second, a highly microporous structure effectively can prevent the infiltration of molten iron and avoid the occurrence of a brittle contact zone.[3–5] Commonly there are two routes toward obtaining a highly microporous structure. The first route is adding silicon, and the second is decreasing the size of the filler grains.[6,7] In our previous work, it has been observed that the addition of appropriate silicon content along with its particle size,[8–10] activated alumina micropowder,[11] electric-calcined anthracite aggregates,[12] and aluminum[13] can be favorable for the formation of an excellent microporous structure. Also, two routes are proposed toward increasing TC: adding a component with high thermal conductivity and densifying the material. Carbon nanotubes (CNTs) have been investigated widely for applications in the past decade because of their unique mechanical and physical properties. Some investigations show that the incorporation of CNTs in polymer-[14] and ceramic-based composites can lead to YAWEI LI, Professor, XILAI CHEN, Ph.D. Student, YUANBING LI, Professor, SHAOBAI SANG, Teacher, and LEI ZHAO, Professor, are with the Hubei Province Key Laboratory of Ceramics and Refractories, Wuhan University of Science & Technology, Wuhan 430081, P.R. China. Contact e-mail: [email protected] Manuscript submitted March 9, 2010. Article published online May 15, 2010 METALLURGICAL AND MATERIALS TRANSACTIONS A
significant improvements in electrical and thermal properties because of CNTs excellent electrical conductivity (106 S/m at 300 K (27 C) for single-walled CNT [SWCNT] and >105 S/m for multiple-walled CNT [MWCNT])[15,16] and thermal conductivity (6600 W/m 9 K for individual SWCNT and >3000 W/m 9 K for individual MWCNT).[17,18] In the case of ceramicbased composites, Jiang and Gao[19] reported that there was a 97 pct enhancement in TC of a TiN-CNT composite at 703 K (430 C) compared with that of TiN because of the presence of 5 wt pct MWNTs. Zhan et al.[20] obtained an electrical conductivity of 3345 S/m for a 15 vol. pct SWCNT–alumina nanocomposite, which represents an increase of 13 orders of magnitude over that of pure alumina. However, until now, few reports can be found in the literature about the effect of CNTs addition on the TC and porosity characteristics of carbon refractories for a BF. This article will address the evolution of TC, as well as the porosity characteristics and microstructures, of BF carbon refractories with added CNTs during heat treatment in a CO-N2 atmosphere. II.
EXPERIMENTAL
A. Raw Materials and Refractories Fabrication Electric-calcined anthracite granules and fine powder (3–5 mm, 1–3 mm, 0–1 mm,
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