Fusion cast refractories

Question 1

What are the characteristics of fusion cast refractories?

Answer 1

~ alumina-zirconia silica (AZS) refractories are fusion cast to form LOW PERMEABILITY refractories for glass manufacture

Question 2

What raw materials are used?

Answer 2

~ alumina and zircon are mixed to form a eutectic liquid liquid comp

Question 3

How does fusion cast occur/what is skull melting?

Answer 3

1. liquid is poured >1800C into resin bonded sand molds
2. after solid surface is formed the molds are stripped away, the casting is buried in an insulating powder for ~2 weeks
3. must aim to minimize shrinkage voids in the casting
4. AZS blocks are cut out of the casting and then assembled into glass tanks

Question 4

What are the qualities of AZS refractories?

Answer 4

~ high corrosion resistance

Question 5

What are the corrosion products? What do they do?

Answer 5

~ 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

Question 6

What part of the microstructure is most vulnerable to corrosion?

Answer 6

~ the glassy portion

~ this portion is necessary to relieve stresses from anisotropic expansion of crystalline grains and polymorphic transformations in ZrO2 grains

Question 7

What fusion cast refractories are the most corrosion resistant against molten glass? What are they used for?

Answer 7

~Cr2O3-Al2O3

~ fiberglass melting tanks

Question 8

What are the downsides to Cr2O3-Al2O3 refractories?

Answer 8

~ soluble chromium ions strongly color the glass