First-principles study of the interfacial adhesion between SiO2 and MoSi2

Upon oxidation, a silica scale forms on MoSi2, a potential high-temperature coating material for metals. This silica scale protects MoSi2 against high-temperature corrosive gases or liquids. We use periodic density functional theory to examine the interface between SiO2 and MoSi2. The interfacial bonding is localized, as evidenced by an adhesion energy that changes only slightly with the thickness of the SiO2 layer. Moreover, the adhesion energy displays a relatively large (0.40J m2) variation with the relative lateral position of the SiO2 and MoSi2 lattices due to changes in Si-O bonding across the interface. The most stable interfacial structure yields an ideal work of adhesion of 5.75J m2 within the local density approximation (5.02J m2 within the generalized-gradient approximation) to electron exchange and correlation, indicating extremely strong adhesion. Local densities of states and electron density difference plots demonstrate that the interfacial Si-O bonds are covalent in character. Mo-O interactions are not found in the SiO2 MoSi2 interface investigated here. Our work predicts that the SiO2 scale strongly adheres to MoSi2, and further supports the potential of MoSi2 as a high-temperature structural material and coating.