First-principles study of the interfacial adhesion betweenSiO2andMoSi2

Abstract

Upon oxidation, a silica scale forms on $\mathrm{Mo}{\mathrm{Si}}_{2}$, a potential high-temperature coating material for metals. This silica scale protects $\mathrm{Mo}{\mathrm{Si}}_{2}$ against high-temperature corrosive gases or liquids. We use periodic density functional theory to examine the interface between $\mathrm{Si}{\mathrm{O}}_{2}$ and $\mathrm{Mo}{\mathrm{Si}}_{2}$. The interfacial bonding is localized, as evidenced by an adhesion energy that changes only slightly with the thickness of the $\mathrm{Si}{\mathrm{O}}_{2}$ layer. Moreover, the adhesion energy displays a relatively large $(0.40\phantom{\rule{0.3em}{0ex}}\mathrm{J}∕{\mathrm{m}}^{2})$ variation with the relative lateral position of the $\mathrm{Si}{\mathrm{O}}_{2}$ and $\mathrm{Mo}{\mathrm{Si}}_{2}$ lattices due to changes in $\mathrm{Si}\text{\ensuremath{-}}\mathrm{O}$ bonding across the interface. The most stable interfacial structure yields an ideal work of adhesion of $5.75\phantom{\rule{0.3em}{0ex}}\mathrm{J}∕{\mathrm{m}}^{2}$ within the local density approximation ($5.02\phantom{\rule{0.3em}{0ex}}\mathrm{J}∕{\mathrm{m}}^{2}$ 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 $\mathrm{Si}\text{\ensuremath{-}}\mathrm{O}$ bonds are covalent in character. $\mathrm{Mo}\text{\ensuremath{-}}\mathrm{O}$ interactions are not found in the $\mathrm{Si}{\mathrm{O}}_{2}∕\mathrm{Mo}{\mathrm{Si}}_{2}$ interface investigated here. Our work predicts that the $\mathrm{Si}{\mathrm{O}}_{2}$ scale strongly adheres to $\mathrm{Mo}{\mathrm{Si}}_{2}$, and further supports the potential of $\mathrm{Mo}{\mathrm{Si}}_{2}$ as a high-temperature structural material and coating.