Why are dense refractories preferred where molten glass contacts a furnace lining?

Dense refractories are preferred for furnace linings in contact with molten glass primarily to prevent corrosion and ensure the longevity of the furnace structure.12

While many refractory materials are intentionally porous to improve resistance to thermal shock, this porosity is undesirable when the material is exposed to corrosive molten substances. In glass-melting furnaces, a porous lining would allow the molten glass to penetrate the refractory, leading to chemical attack and degradation of the furnace walls. By utilizing materials with higher density and lower porosity, manufacturers create a barrier that is comparatively inert and resistant to the corrosive action of the glass melt.13

Commonly used dense materials include:
* Flux blocks: Highly siliceous, dense fireclay bricks used specifically in areas contacting the melt.3
* Fused alumina and mullite bricks: These offer excellent durability and prevent glass penetration.3
* Zirconia and zircon refractories: These are valued for their lack of porosity, volume stability, and high resistance to chemical attack by molten glass.43
* Electrocast alumina-zirconia-silica: These high-density materials are often employed in large melting chambers to ensure a long, trouble-free service life.2