Fig. 6: Transmission electron microscopy (TEM) characterization of a Type II slag found on an un-melted surface.

Scanning TEM (STEM) high angle annular dark field (HAADF) and corresponding STEM energy dispersive X-ray spectroscopy elemental maps of the slag and of the native surface oxide away from the slag are shown in (a) and (b), respectively. The region where the TEM sample was lifted out by focus ion beam is presented in Supplementary Fig. 6c. c, d A top view and a cross section view of a Type II slag after corrosion testing.