Why do mullite firebricks resist damage from molten glass?

Mullite firebricks are highly valued in the glass industry because they possess excellent durability when exposed to molten glass. Their resistance to damage is primarily due to two factors:1

• Chemical Inertness: Mullite is comparatively inert chemically, meaning it does not readily react with or degrade when in contact with molten glass.1
• Low Permeability: These bricks are manufactured to be dense, which prevents the molten glass from penetrating the material.1

As a stable aluminosilicate compound, mullite maintains its structural integrity at very high temperatures, with a melting point of approximately 1,850° C (3,360° F). Because of these properties, mullite refractory materials are effectively utilized in critical areas of glass-melting furnaces, such as the forehearth roofs.2