What role does partial vitrification play in making clay-based refractories?

In the production of clay-based refractories, partial vitrification serves as a critical liquid-sintering process that bonds particles together to provide structural integrity and consolidation.12

During firing in a kiln, the clay component undergoes partial vitrification, forming a glassy liquid phase. This process plays two primary roles:1

• Bonding and Densification: The liquid phase facilitates liquid-phase sintering by promoting a denser rearrangement of particles through viscous flow. Subsequently, through solution-precipitation, smaller particles and surfaces of larger particles dissolve and reprecipitate at the "necks" connecting the larger particles, which reduces porosity and forms strong bonds.1
• Maintaining Rigidity: By ensuring that only a portion of the material becomes liquid, the remaining solid particles help maintain the shape of the ceramic piece during firing, minimizing the risk of sagging or warpage.1

The extent of glass formation and the resulting residual porosity are controlled by adjusting the ingredients and the duration the material is held at its maximum firing temperature.1