Atomic transport properties of water in barium–strontium aluminosilicates: Coupling of reactions and diffusion

Barium–strontium aluminosilicate (BSAS), with excellent resistance to water vapor corrosion and low water permeability, is considered an ideal environmental barrier coating material. Water vapor plays an important role on the failure of BSAS when it is exposed to service environments. Herein, the atomic transport properties of water in BSAS are investigated using ab initio calculations. The metastable structure of water in BSAS mainly consists of hydroxyl group and H⁺, where the hydroxyl group mainly exists in the form of Al–OH structure. In BSAS crystals, water first reacts with the aluminosilicate network to form metastable hydroxyl group and H⁺, and then hydroxyl group and H⁺ diffuse through the aluminosilicate network. Alkaline earth elements limit the diffusion behavior of water and improve the resistance to water vapor corrosion by maintaining the desired local charge balance of the Al–O₄ tetrahedron structure. Furthermore, the ab initio molecular dynamics calculations at service temperature and pressure of BSAS are carried out to verify the above conclusions.