2. Ingot production

2.1 Ingot smelting

As with other reactive or refractory metals, the melting of Zr or Hf and their alloys is dominated by the following features:

• the very high reactivity of Zr or Hf towards air and most of the other gases already mentioned, which means they have to be melted in a vacuum or in an extremely pure neutral gas;

• very high melting point: 1850°C for Zr and 2225°C for Hf ;

• the aggressiveness of molten metal towards crucibles: it reduces or dissolves almost all known refractories, including graphite. At laboratory level, alloy fusions in a Yttrin crucible (Y ₂ O _3-x ) have...