In the shown example, we can see a microstructure that is reminiscent of the solidification of a multicomponent melt, a slag from an industrial process in this case. In such a multicomponent melt, some crystals from early, which are then free to grow...

During high-temperature processes conducted under atmospheric conditions, a small quantity of the process materials will evaporate and form a vapor pressure of their compounds in the surrounding atmosphere.

As more oxygen becomes available, more metals will reach their oxide saturation limit, and new oxides will form.