Explanatory notes
… ‑niobium (12) Ferro ‑silico‑magnesium and ferro‑silico‑calcium. The heading excludes : (a) Chemical products … in the same way as ferro‑alloys, such as molybdenum oxide, calcium molybdate and silicon carbide, and also, if they contain less than 4 % by weight of iron, calcium silicide and manganese silicide ( Chapter 28 ). …