Did you read TFA? It says. "In this very simple process, the salt acted as a heat absorber while the magnesium removed oxygen from the quartz, resulting in pure silicon. "
So the article does indeed 'suggest' that Mg is removing O. My question was concerning how is this oxygen removal related to creating porosity. Or not.
In any case, it seems likely that some formerly filled space must be vacated to create porous openings.
Does anyone know how this happens?