Fusion cast refractories Flashcards
What are the characteristics of fusion cast refractories?
~ alumina-zirconia silica (AZS) refractories are fusion cast to form LOW PERMEABILITY refractories for glass manufacture
What raw materials are used?
~ alumina and zircon are mixed to form a eutectic liquid liquid comp
How does fusion cast occur/what is skull melting?
- liquid is poured >1800C into resin bonded sand molds
- after solid surface is formed the molds are stripped away, the casting is buried in an insulating powder for ~2 weeks
- must aim to minimize shrinkage voids in the casting
- AZS blocks are cut out of the casting and then assembled into glass tanks
What are the qualities of AZS refractories?
~ high corrosion resistance
What are the corrosion products? What do they do?
~ corrosion products Al2O3, SiO2 are glass constituents that don’t negatively effect quality
~ increase viscosity of glass near the refractory walls, allowing the glass to contain itself
What part of the microstructure is most vulnerable to corrosion?
~ the glassy portion
~ this portion is necessary to relieve stresses from anisotropic expansion of crystalline grains and polymorphic transformations in ZrO2 grains
What fusion cast refractories are the most corrosion resistant against molten glass? What are they used for?
~Cr2O3-Al2O3
~ fiberglass melting tanks
What are the downsides to Cr2O3-Al2O3 refractories?
~ soluble chromium ions strongly color the glass