Hot Corrosion Resistance of Aluminosilicate Refractories – Comparative Tests in the Secondary Combustion Chamber of a Hazardous Waste Incinerator
After the exposure, the samples were analysed in the laboratory regarding porosity and mineralogical changes.
The test results show that degradation is caused by hot corrosion, specifically by condensed thenardite (Na2SO4). Free silica, largely accessible in fireclay bricks, is the first phase that reacts with thenardite. The reaction generates liquid natrosilite (Na2Si2O5). This low melting phase leads to deformation and creep of hotter brick parts. In a next step, natrosilite reacts with mullite forming albite (NaAlSi3O8). Simultaneously, thenardite reacts directly with mullite forming nosean (Na8Al6Si6O28S).
In order to better withstand the hot corrosion mechanism, refractories should contain as little silica as possible.