Hot corrosion behaviour of barium-strontium aluminosilicates in a molten Na₂SO₄ environment

The hot corrosion behaviour of barium-strontium aluminosilicates (B_1−xS_xAS) attacked by Na₂SO₄ was investigated in the temperature range from 900 to 1100 °C and the weight change was measured as a function of the corrosion time. The surfaces and cross-sections of the corroded samples were observed by scanning electron microscopy in backscattered electron mode and energy-dispersive X-ray spectroscopy. The phase composition was characterized by X-ray diffraction. The results indicate that the hot corrosion of B_1−xS_xAS by molten Na₂SO₄ was controlled by a diffusion-reaction mechanism. The strontium and/or barium cations diffused out of their aluminosilicate network, and the vacant sites were filled by sodium cations diffusing into the structure to form a NaAlSiO₄ on the top. Due to their smaller radius, the strontium atoms showed a faster diffusion rate than the barium atoms. The corrosion depth significantly increased with the temperature and the strontium concentration in the B_1−xS_xAS.