Technical Paper
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At low temperatures the typical alkalis such as sodium and potassium react with alumina-silica
the in the refractory materials
forming different solid state minerals such as Feldspar which have a larger crystal structure than the original mineral, causing break-up of the microstructure. This is a very complex mechanism and may be accompanied by selective parts of a refractory material that melt due to the formation of low temperature eutectic
compositions within the corrosive atmosphere. Higher atmospheric temperatures will dramatically increase the formation of low viscosity
liquid phases inside the refractory
material which will cause rundown of the refractory
material, considered as a slag.
Refractory linings can literarily melt away in a very short time.
Figure 6: Although high alumina is often used when faced with aggressive environments, the formation of β-alumina is a serious problem. In this image the lower grade alumina melted away at a very similar rate than the chemical spalling of the higher grade alumina. This indicates that a quality somewhere in between is more likely required
The biggest fear for any refractory designer is to choose a material which could potentially melt and therefore materials with a higher alumina content is often chosen. The art in the selection of material is to choose a material that will form high viscosity liquid phases that will not run down, but will seal and protect the surface of
Figure 7: Understanding the process conditions is vital to the correct selection of materials. This is often only possible to establish after the unit has been in operation for a while
20 ENGINEER THE REFRACTORIES May 2018 Issue
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