Characterization and sinterability of chemically precipitated phosphate-bearing magnesia grains

Two brucite powders having different impurity levels and doped with 0.5 mol% P2O5 were coprecipitated from MgCl2-rich solutions derived from natural magnesite rock. The precipitated powders were characterized for their chemical and mineralogical compositions, thermal analyses and particle size distribution as well as particle morphology. The effect of P2O5 as well as other impurities on densification, phase composition and microstructure of the dense-magnesia grains processed by two-stage firing process up to 1300–1550°C was discussed. Phase composition was qualitatively determined by XRD, whereas a SEM attached with an EDS unit was applied for investigating microstructure. The results reveal that dense periclase ceramics containing 93–96% MgO with variable degree of direct bonding could be obtained by firing the precipitated brucite pellets up to 1300–1550°C. Brucite doped with 0.5 mol% P2O5 has contributed in densification of magnesia grains in the presence of magnesia-rich calcium silicate, ferrite and phosphate liquid phase. As the impurity content increases, densification is accelerated and occurs as low as 1300°C with relative decrease in bulk density and degree of direct bonding.