COMPOSITION OF MELILITES CRYSTALLIZED FROM CAO-AL2O3-FE2O3-SIO2 MELTS

High alumina cements are usually made by a fusion process in which the components are melted, cast into ingots and allowed to crystallise. It has proved difficult to predict and control the mineralogical composition of the melt-ceramic product, termed clinker. The clinker mineralogy is known to be sensitive to the bulk SiO2 content, which is typically only 2-6 wt-%. This study provides data on laboratory simulant clinkers, melted and allowed to cool at rates of 5 and 300 K min-1. The charges were selected to yield, upon crystallisation, a melilite close to gehlenite, Ca2 (Al,Fe)2SiO7. Analyses of the melilite actually present in undercooled charges, containing 2-6% Wt-%SiO2, disclose that melilite crystallises with a substantial deficit of Si relative to its nominal composition: this deficit is approximately charge balanced by additional trivalent ions, Al3+ and Fe3+. The implications to clinker mineralogy and reactivity are discussed. (C) 1993 The Institute of Materials.