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How does magnesia help alumina become translucent during sintering?

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Steps in doctor blading, a tape-casting process employed in the production of ceramic films. Ceramic powder and solvent are mixed to form a slurry, which is treated with various additives and binders, homogenized, and then pumped directly to a tape-casting machine. There the slurry is continuously cast onto the surface of a moving carrier film. The edge of a smooth knife, generally called a doctor blade, spreads the slurry onto the carrier film at a specified thickness, thereby generating a flexible tape. Heat lamps gently evaporate the solvent, and the dry tape is peeled away from the carrier film and rolled onto a take-up reel for additional processing.
advanced ceramics Steps in doctor blading, a tape-casting process employed in the production of ceramic films. Ceramic powder and solvent are mixed to form a slurry, which is treated with various additives and binders, homogenized, and then pumped directly to a tape-casting machine. There the slurry is continuously cast onto the surface of a moving carrier film. The edge of a smooth knife, generally called a doctor blade, spreads the slurry onto the carrier film at a specified thickness, thereby generating a flexible tape. Heat lamps gently evaporate the solvent, and the dry tape is peeled away from the carrier film and rolled onto a take-up reel for additional processing.

In its pure state, alumina does not sinter to translucency because residual pores trapped within the growing grains scatter light, rendering the material opaque.1

When magnesia is added as a sintering aid, it facilitates translucency by slowing the migration of grain boundaries during the sintering process. By restricting this movement, magnesia ensures that pores remain located on the grain boundaries rather than becoming trapped inside the grains. Once positioned on the boundaries, these pores can be effectively eliminated through grain boundary diffusion, allowing the ceramic to reach extremely low porosities and achieve optical translucency.12