this is neither what smelting is or what CVD is. smelting goes from oxide to metal, and uses carbon monoxide at ~atmospheric pressure for that. early smelting was used for smelting, but early purification method was forging. there’s Mond process, but it’s not smelting. CVD occurs in vacuum and uses something probably rather reactive on its own that decomposes on target surface, sometimes giving one atomic layer at a time, and it doesn’t have to be metal