The phase composition of mixtures in corundum-rich Al2O3-CaO-P2O5 systems

This paper presents the results of the phase composition study of model systems containing all the main components of the mixtures, used in the laboratory tests of concretes, namely, Al2O3, CaO and P2O5. Samples were analysed using X-ray analysis and scanning electron microscopy with EDS analysis in microregions. Four mixtures were tested: one corundum-rich with a small amount of aluminium phosphate and calcium oxide, and three with a high content of aluminium phosphate with the addition of calcium oxide and calcium aluminate. Mixtures to which phosphoric acid was added instead of aluminium phosphate were also studied. It was found that in the model mixtures corresponding to the composition of corundum refractory concretes with small amount of phosphates, two phases are formed, during operation at a temperature of 1400 °C, namely Ca3(PO4)2 and Ca(Al12O19). The addition of phosphoric acid resulted in the concrete having the same phase composition as it would had aluminium phosphate and alumina cement been added instead.