Investigation of the synthesis and the alkali corrosion of potassium aluminosilicates by XRD and NMR (29Si, 27Al)

Alkali aluminosilicates are potential materials for high temperature applications under alkali load. This study investigated the corrosion behaviour of potassium aluminosilicates of the nominal compositions of KAlSi2O6 and KAlSiO4 synthesized at different temperatures and dwell times and exposed to alkali load at 1100 °C. For understanding the corrosion behaviour depending on the synthesizing parameters, the produced materials and corroded samples were investigated by XRD and NMR spectroscopy (29Si, 27Al). The combination of both analytical techniques showed that characteristics of the synthesized materials on a structural level played an important role for the corrosion behaviour. It was shown that amorphous and disordered components in the samples occurred which were not registered by XRD. The application of 29Si and 27Al NMR spectroscopy yielded that materials having already after synthesis a structural arrangement similar to the equilibrium target phase of the batch showed a high structural stability under alkali load and gave positive results in the applied corrosion test. Materials with large structural rearrangements during alkali load exhibited volume changes and therefore failed the corrosion test. Based on these observations it should therefore be possible to design materials with high chemical and mechanical stability suitable as furnace linings and to evaluate end-of-life aluminosilicates for an application as alkali corrosion resistant recyclates.