Effects of Different Barium Compounds on the Corrosion Resistance of Andalusite-Based Low-Cement Castables in Contact wi
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ALUMINUM manufacturing is an energy-intensive process in which a quarter of the energy consumed is used for melting and holding furnace operations.[1] The melting furnaces usually operate over the temperature range 973 K to 1673 K (700 C to 1400 C),[2,3] and their refractory linings undergo corrosive failure because of molten metal reactions.[3,4] These reactions lead to the formation of an interfacial buildup on the refractory surface, which reduces the efficiency and service life of the refractory lining.[5] The formation of these deposits is associated with stress fractures, whereas their removal by scraping can damage the lining. Refractories used in the middle portion of a furnace, also known as the ‘‘belly band’’ zone, are more prone to extensive corrosion because it is always in contact with molten aluminum.[6] Refractory corrosion by molten metals/alloys begins with the initiation of wetting reactions at the interface and is subsequently followed by metal penetration and formation of secondary phases such as corundum or spinel.[7–11] Generally, the area affected by corrosion through reactions with molten aluminum appears as a ESMAEIL ADABIFIROOZJAEI and EBAD RASTKERDAR, Graduate M.Sc. Students, are with the Department of Materials Engineering, Isfahan University of Technology, Isfahan 8415683111, Iran. Contact e-mail: e.adabifi[email protected] PRAMOD KOSHY, Research Associate, is with the School of Materials Science and Engineering, University of New South Wales, Sydney, NSW 2052, Australia. Manuscript submitted December 24, 2010. Article published online April 30, 2011. METALLURGICAL AND MATERIALS TRANSACTIONS B
black zone in the refractory material. Sometimes, the corroded area appears as a composite material, comprising mainly small grains of corundum surrounded by an interconnected metallic network.[12] The differences in the coefficients of thermal expansion between the alumina layer formed and the original refractory results in increased thermal loading on the alumina layer, causing it to separate from the refractory, which provides more pathways that lead to enhancement in the corrosion rate.[13] Several factors influence the refractory reactions with Al alloys. The effect of physical properties (porosity, surface roughness, and particle sizes) as well as the processing conditions on the interfacial behavior of Al/ refractory systems has been well documented.[14–22] However, the refractory composition has a greater influence on refractory corrosion by molten aluminum alloys.[23] To decrease the corrosion, refractory manufacturers add chemical additives (nonwetting agents) such as BaSO4, CaF2, and AlF3 to the refractory material.[24] Recent studies have suggested that, in aluminosilicate refractory castables, the positive performance of the additives is related to the conversion of free silica in the refractory into chemically stable phases.[24,25] Even though the formation of glassy phases is believed to be counterintuitive to the performance of refractories, glassy phases comprising barium, calciu
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