185 BOLETIN DE LA SOCIEDAD ESPAÑOLA DE A R T I C U L O Cerámica y Vidrio Belite Portland Clinkers. Synthesis and Mineralogical Analysis A. G. DE LA TORRE, 1* M. A. G. ARANDA, 1 A. H. DE AZA, 2 P. PENA 2 and S. DE AZA 2 1 Departamento de Química Inorgánica, Universidad de Málaga, Teatinos s/n, 29071 Málaga, Spain 2 Instituto de Cerámica y Vidrio, CSIC, c/ Kelsen nº 5, Campus de Cantoblanco, 28049 Madrid, Spain. * mgd@uma.es The quaternary system CaO-SiO 2 -Al 2 O 3 -Fe 2 O 3 has been taken into account to design five compositions of belite Portland clinkers with belite (Ca 2 SiO 4 ) contents ranging from 60 to 65 wt%, located in its primary phase field of crystallization. The synthesis of these belite clinkers has been studied by high temperature microscopy, dilatometry, differential thermal analysis and thermogravimetric analysis. As a result, the optimum clinkerization temperature has been established at 1360 ± 5ºC. The quantitative phase analyses of the clinkers were carried out by X-ray powder diffraction with the Rietveld methodology. The mineralogical composition depends on the initial dosages, on the highest temperature achieved and on the time of residence at this temperature. The reaction was completed at 1365ºC during 15 min (free CaO <0.5 wt%), in those conditions the β-belite form is stabilized and the harmful transformation β→γ is avoided. Keywords: Belite Portland clinkers, Phase Equilibrium Diagrams, Rietveld Method Clínqueres Pórtland Belíticos. Síntesis y Análisis Mineralógico. Teniendo en cuenta el sistema cuaternario CaO-SiO 2 -Al 2 O 3 -Fe 2 O 3 , se han diseñado cinco composiciones de clínqueres Pórtland belíticos, con contenidos del 60 y del 65% en peso de belita (Ca 2 SiO 4 ), situadas en su campo primario de cristalización. La síntesis de estos clínqueres belíticos se ha estudiado “in situ” por microscopía de alta temperatura, dilatometría y análisis térmico diferencial y termogravimétrico. La temperatura óptima de clinquerización, determinada con estas técnicas, ha sido de 1360 ± 5ºC. Los análisis cuantitativos de los clínqueres se llevaron a cabo por difracción de rayos-X con la metodología Rietveld. Los porcentajes de las diferentes fases dependen de las dosificaciones iniciales, de la temperatura alcanzada y del tiempo de residencia a dicha temperatura. Se ha conseguido una reacción total (%CaO libre < 0.5% en peso) tratando a 1365ºC durante 15 min, en cuyas condiciones se estabiliza la forma β de la belita y se evita la transformación perjudicial β→γ. Palabras clave: Clínqueres Pórtland belíticos, diagramas de equilibrio, método de Rietveld. 1. INTRODUCTION The production of one ton of standard Portland cement releases into the atmosphere 0.54 ton of CO 2 resulting from the decomposition of calcite. In addition, the process uses vast amounts of energy, particularly for clinkering and milling. Thus, to obtain a ton of cement requires to use 60–130 kg of fuel and an average 110 Kwh of power, which result in the release of CO 2 resulting from oxidation of the fuel in the furnace and from the use of fossil fuels to obtain electrical power. The production of Portland cement using coal as fuel releases ~ 0.97 ton of CO 2 per ton of clinker. The overall CO 2 emissions of the cement industry are ~ 6% of all anthropogenic carbon dioxide and account for 4% of the global warming of the planet (1). Finding effective ways of reducing such emissions should therefore be a strong research priority. The production of belite Portland cements is one of such solution as it releases decreased amounts of CO 2 . Standard Portland clinker contains four major crystalline components, namely: alite (Ca 3 SiO 5 ), belite (Ca 2 SiO 4 ), ferrite (Ca 4 Al 2 Fe 2 O 10 ) and tricalcium aluminate (Ca 3 Al 2 O 6 ), in approximate proportions of 60, 15, 10 and 10 wt%, respectively (2). In cement nomenclature, these components are designated C 3 S, C 2 S, C 4 AF and C 3 A, respectively, with C = CaO, S = SiO 2 , A = Al 2 O 3 and F = Fe 2 O 3 . The formation of the principal component, alite, requires the use of a clinkering temperature of about 1450 ºC in the furnace in the absence of additional melting agents. Conversely, belite Portland clinkers contain more than 50 wt% of belite as the main crystal phase, in addition to alite, ferrite and tricalcium aluminate (3). These clinkers therefore contain less calcium than do standard Portland cements; as a result, their production releases less CO 2 from the decomposition of calcite into the atmosphere (0.50 ton CO 2 per ton of clinker). In addition, the optimum clinkerization temperature for these clinkers is roughly 100 ºC lower than that for standard Portland clinker, which helps to reduce CO 2 emissions from fuel burning. Bol. Soc. Esp. Ceram. V., 44 [3] 185-191 (2005)