The effects of sodium on the growth velocity and growth morphology of silicon in Al-Si alloys

The effects of sodium additions to Al-Si alloys have been studied by determining the coupled zone for normal and "modified" alloys. Sodium slows the growth rate of silicon with respect to aluminum, and changes the morphology of the silicon. These effects were observed to be independent of growth temperature. A hypothesis that sodium adsorbs on the fast-growing faces of silicon can explain all observations.