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 m agnesite rock. The precipitated powders were characterized for their chemic al and mineralogical compositions, thermal analyses and particle size distr ibution as well as particle morphology. The effect of P2O5 as well as other impurities on densification, phase composition and microstructure of the d ense-magnesia grains processed by two-stage firing process up to 1300-1550 degreesC was discussed. Phase composition was qualitatively determined by X RD, whereas a SEM attached with an EDS unit was applied for investigating m icrostructure. The results reveal that dense periclase ceramics containing 93-96% MgO with variable degree of direct bonding could be obtained by firi ng the precipitated brucite pellets up to 1300-1550 degreesC. 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 liqui d phase. As the impurity content increases, densification is accelerated an d occurs as low as 1300 degreesC with relative decrease in bulk density and degree of direct bonding. (C) 2001 Elsevier Science Ltd and Techna S.r.l. All rights reserved.