Hot corrosion behavior of Lu₂SiO₅ and La₂SiO₅ in a molten Na₂SO₄ environment: A first-principles corrosion resistance investigation

The hot corrosion behavior of Lu₂SiO₅ and La₂SiO₅ (RE₂SiO₅, RE: rare earth) under Na₂SO₄ attack was investigated at temperatures ranging from 900 to 1100 °C. First-principles quantum mechanical calculations based on the density functional theory (DFT) were used to obtain the electronic structures of RE₂SiO₅. The results indicated that the hot corrosion behavior of these compounds depended on their crystal structure and the structural stability of various corrosion products. First-principles results revealed that the RE–O bond was easier to break than the Si–O bond under molten Na₂SO₄ corrosion environment. In this process, Na⁺ cations partly substitute RE³⁺ cations to form NaRE silicates. Once NaRESiO₄ was initially formed, cyclosilicate and apatite phases were produced sequentially as the temperature and extent of corrosion increased. In addition, Lu₂SiO₅ exhibited higher corrosion stability than La₂SiO₅ because of the lower distortion of the RE–O coordinated polyhedral. The Lu–O bonds showed higher bonding strengths than the La–O bonds as revealed by the density of state (DOS) and Mulliken population analyses. Furthermore, the stability of the formed NaRESiO₄ increased upon decreasing the size of the RE³⁺ cation. Therefore, Lu₂SiO₅ was more readily formed than NaLuSiO₄, and La₂SiO₅ was prone to form oxyapatite NaLa₉Si₆O₂₆ after undergoing corrosion with Na₂SO₄. Overall, Lu₂SiO₅ showed better corrosion resistance to Na₂SO₄ than La₂SiO₅.