Preparation of Self-Coating Al2O3 Bonded SiAlON Porous Ceramics Using Aluminum Dross and Silicon Solid Waste under Ambient Air Atmosphere.

Al2O3-bonded SiAlON ceramic with self-coating was prepared using aluminum dross and silicon solid waste as starting materials under ambient air conditions. The changes in phase, microstructure, and physical properties of the ceramic with temperature were analyzed and the formation mechanism of the SiAlON phase was elucidated. The results showed that higher temperature was more suitable for the preparation of SiAlON ceramics. As the temperature increased from 1400 to 1600 °C, the main phases in the ceramic transformed from mullite, Al2O3, and SiAlON to Al2O3 and SiAlON. An Al2O3-rich layer spontaneously coated the surface of the porous ceramic as Al melted and oxidized at high temperature. The thickness of this layer decreased as the temperature increased. The presence of Al2O3-rich coating layer impeded air flow, allowing nitriding of Si and Al, and the formation of the SiAlON phase in ambient air conditions. This study not only presents a strategy to successfully recycle aluminum dross and silicon solid waste but also offers a straightforward approach to preparing SiAlON material in air atmosphere.

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-3 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-3 for all thicknesses. Moreover, the defects in vacuum-compacted magnesia samples are mainly in the form of small circular pores.