Fusion cast refractories Flashcards

1
Q

What are the characteristics of fusion cast refractories?

A

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

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2
Q

What raw materials are used?

A

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

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3
Q

How does fusion cast occur/what is skull melting?

A
  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
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4
Q

What are the qualities of AZS refractories?

A

~ high corrosion resistance

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5
Q

What are the corrosion products? What do they do?

A

~ 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

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6
Q

What part of the microstructure is most vulnerable to corrosion?

A

~ the glassy portion

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

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7
Q

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

A

~Cr2O3-Al2O3

~ fiberglass melting tanks

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8
Q

What are the downsides to Cr2O3-Al2O3 refractories?

A

~ soluble chromium ions strongly color the glass

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