The relationship between phase composition and conditions of sintering seawater derived magnesium oxide

Abstract

This study has focused on the favourable effect of the TiO2 addition (1, 2 and 5 wt%) on the reduction of B2O3 content during activated sintering of magnesium oxide from seawater at temperatures of 1400, 1500 and 1700°C for the duration of 1, 2 and 4 h. A mathematical model of dependence between the B2O3 mass fraction in the sintered sample, the temperature of isothermal sintering, the isothermal sintering time and the mass fraction of TiO2 added have been proposed. Magnesium oxide was obtained from seawater by substoichiometric precipitation, with the addition of 80% of dolomite lime as the precipitation agent. New phases formed in magnesium oxide samples were examined by the XRD and SEM/EDS analysis. The results indicate that during activated sintering of seawater-derived magnesium oxide with a TiO2 addition, reactions of formation of Ca2B2O5, CaTiO3 and Mg2TiO4 took place simultaneously. The thermodynamics analysis of experimental results, based on the Onsager reciprocity relations (symmetry relations), was applied and phenomenological coefficients were calculated to describe the interference of these three irreversible processes.