Sinterability of magnesium-oxide powder containing spherical agglomerates

The magnesium-oxide (MgO) powders were prepared by calcining basic magnesium carbonate (4MgCO₃·Mg(OH)₂·4H₂O; BMC) powder at a temperature between 600°C and 1200°C for 1 to 5 h. The resulting MgO powders contained spherical agglomerates with diameters of 10–50 m; the external shapes of these BMC agglomerates remained unchanged even after the calcination. With increasing compaction pressure, the densification of MgO powder compacts proceeded by (i) the rearrangement of agglomerates (50 MPa), (ii) the collapse of agglomerates (50–100 MPa), and (iii) the closer packing of primary particles (100 MPa). The MgO compact was fired at 1400 °C for 5 h. The relative density of the sintered MgO compact whose starting powder was prepared by calcining the BMC at 1000°C for 3 h attained 98.0%. The bending strength of this sintered MgO compact attained 214 MPa.