Silica refractories

Question 1

How are the bricks for silica refractories made?

Answer 1

> pressed/extruded with a SULPHATE LYE BINDER (wood sugar, paper byproduct)
small amounts of lime (~3%) are added
heated slowly to 600C to prevent cracking from VOLUME CHANGE due to 573C alpha–>beta quartz polymorphic transformation
at 1450C: wollastonite bonds with cristobalite and tridymite form upon firing, and are retained as metastable (liquid –> silicate glass) upon cooling

Question 2

To what degree do silica refractories retain their strength?

Answer 2

> up to a few degrees of eutectic melting (1436C)

Question 3

What are the applications of silica refractories?

Answer 3

> coke ovens: heated to 600C over 10 weeks, operated above this temp for over 25 years
used in GLASS TANK CROWN STRUCTURES

Question 4

What is tridymite?

Answer 4

> Ca-doped SiO2

Question 5

What is cristobalite?

Answer 5

> high temp polymorph of SiO2