A novel approach for magnesia hydration assessment in refractory castables

Abstract

Magnesium oxide (MgO) or magnesia is one of the most important raw materials in the refractory industry. Because of its high refractoriness (melting point of 2800 °C) and corrosion resistance, the presence of this oxide in refractory compositions promotes an increase in the performance of pre-shaped linings for steel production [C.M. Peret, J.A. Gregolin, L.I.L Faria, V.C. Pandolfelli, Patent generation and the technological development of refractories and steelmaking, Refract. Appl. News, submitted for publication; M. Rigaud, Z. Ningsheng, Major trends in refractories industry at the beginning of the 21st century, China's Refract. 11 (2) (2002) 3–8; W.E. Lee, R.E. Moore, Evolution of in-situ refractories in the 20th century, J. Am. Ceram. Soc. 81 (6) (1998) 1385–1410; A. Nishikawa, Technology of monolithic refractories, Tokyo: Technical report No. 33-7, PLIBRICO Japan Co. Ltd, 1984, pp. 98–101]. Nevertheless, in refractory castables formulations, magnesia additions are restricted to coarse particles (usually above 50 μm) and contents of up to 10 wt.% due to their high tendency to react with water and the following great volumetric expansion promoted by this reaction [G.K. Layden, G.W. Brindley, Kinetics of vapor-phase hydration of magnesium oxide, J. Am. Ceram. Soc. 46 (11) (1963) 518–522; A. Kitamura, K. Onizuka, K. Tanaka, Hydration characteristics of magnesia, Taikabutsu Overseas 16 (3) (1995) 3–11; A. Yoschida, T. Nemoto, A. Kaneyasu, Evaluation method for hydration resistance of magnesia fine powder and effect of B 2O 3 content in magnesia raw materials, in: Proceedings of UNITECR’ 2003, 2003, pp. 21–30; R.A. Wogelius, K. Refson, D.G. Fraser, G.W. Grime, J.P. Goff, Periclase surface hydroxylation during dissolution, Geochim. Cosmochim. Acta 59 (9) (1995) 1875–1881; A. Kaneyasu, S. Yamamoto, A, Yoshida, Magnesia raw materials with improved hydration resistance, Taikabutsu Overseas 17 (2) (1996) 21–26; P. Brandão, G.E. Gonçalves, A.K. Duarte, Mechanisms of hydration/carbonation of basic refractories—Part I, Refract. Appl. News 3(2) (1998) 6–9; P. Brandão, G.E. Gonçalves, A.K. Duarte, Mechanisms of hydration/carbonation of basic refractories—Part II: investigation of the kinetics of formation of brucite in fired basic bricks, Refract. Appl. News 3 (2) (1998) 9–11; P. Brandão, G.E. Gonçalves, A.K. Duarte, Mechanisms of hydration/carbonation of basic refractories—Part III, Refract. Appl. News 8 (6) (1998) 23–26; S. Chatterji, Mechanism of expansion of concrete due to the presence of dead-burnt CaO and MgO, Cem. Concr. Res. 25 (1) (1995) 51–56] . Despite the great number of studies describing the behavior of powdered magnesia or high-magnesia bricks, not much research has systematically been done related to its hydration behavior in castables [A. Yoschida, T. Nemoto, A. Kaneyasu, Evaluation method for hydration resistance of magnesia fine powder and effect of B 2O 3 content in magnesia raw materials, in: Proceedings of UNITECR’ 2003, 2003, pp. 21–30; S. Chatterji, Mechanism of expansion of concrete due to the presence of dead-burnt CaO and MgO, Cem. Concr. Res. 25 (1) (1995) 51–56; T.A. Bier, C. Parr, C. Revais, H. Fryda, Chemical interactions in calcium aluminate cement based castables containing magnesia, in: Proceedings of UNITECR’ 1997, 1997, pp. 15–21; D. Jeong, H. Kim, Y. Kim, S. Lee, Development and application of basic dam block for Tundish, J. Tech. Assoc. Refract. Japan 23 (1) (2003) 4–10; K.G. Ahari, J.H. Sharp, W.E. Lee, Hydration of refractory oxides in castable bond systems—I: alumina, magnesia and alumina–magnesia mixtures, J. Eur. Ceram. Soc. 22 (2002) 495–503; K.G. Ahari, J.H. Sharp, W.E. Lee, Hydration of refractory oxides in castable bond systems—II: alumina–silica and magnesia–silica mixtures, J. Eur. Ceram. Soc. 23 (2003) 3071–3077; Y. Koga, M. Sato, K. Sekeguchi, S. Iwamoto, Effects of alumina cement grade and additives on alumina–magnesia castable containing aluminum lactate, Taikabutsu Overseas 18 (1) (1997) 43–47] . In this paper, aspects of magnesia hydration were briefly reviewed. Novel insights concerning magnesia hydration products generated under different curing conditions were attained adapting techniques already used in castables study.