The gaseous medium as a factor in the formation and service of mullite and mullite-corundum refractories

Conclusions

In an investigation of the sintering of mullite and mullite-corundum chamottes in oxidizing and reducing media it was established that kaolin conversion and mullite formation set in a hydrogen atmosphere about 100°C sooner than in an oxidizing medium.

At 1300–1500°C in a reducing medium the corundum crystallizes rapidly as a result of the break-up of the mullite so that the density and strength increase and sintering is delayed to some extent. High-density mullite and mullite-corundum chamottes can be obtained by firing up to 1700°C in an oxidizing medium.

When tested in the lining of carbon black reactors and in the checker of a generator mullite-corundum refractories proved to be more durable than other industrial grade refractories. The saving accruing from their introduction is considerable.

The maximum permitted service temperature in the linings and checkers of heat-using equipment should be governed by the proportion of reducing agent (H₂, CO, C) in the gaseous medium.