Effects of the Molding Method and Blank Size of Green Body on the Sintering Densification of Magnesia

The bulk density of sintered magnesia is significantly influenced by molding methodology and blank size of the green body during dry pressing. The entrapped air in the green body plays a critical role in determining the bulk density of magnesia samples. Herein, high-density magnesia samples, with different sizes, are prepared by using vacuum compaction molding and conventional compaction molding. The physical properties, such as bulk density and pore size distribution, and morphology or as-sintered magnesia samples were characterized by using Archimedes method, mercury porosimetry, and scanning electron microscopy (SEM). The results indicate that the bulk density of conventional compaction magnesia samples decreased below 3.40 g·cm with the increase of thickness due to the presence of entrapped-air induced large pores and intergranular cracks. In addition, the large pores and intergranular cracks in conventionally-compacted samples are observed by SEM images. However, vacuum compaction of magnesia samples resulted in a bulk density of higher than 3.40 g·cm for all thicknesses. Moreover, the defects in vacuum-compacted magnesia samples are mainly in the form of small circular pores.