Wettability of Halides with Molten Metals. Physico-Chemical and Practical Aspects

A study is made on the wettability of sodium chloride and oxygen-free ionic compounds ― fluorides of alkaline-earth elements (CaF, MgF, BaF) ― by molten metals. The metals Cu, Sn, Ag, Au, In, and Ga do not wet these materials (θ ∼ 120-140 deg). The wettability of fluorides by aluminum is somewhat greater (θ ∼ 90-100 deg), in accordance with the greater chemical affinity of aluminum for fluorine. Chemically highly active and aggressive alloys of Ti, Zr, Hf, and V (with concentrations up to 70-80%) which completely wet and destroy known refractory materials (oxide, nitride, carbide, and carbon refractories, etc.) behave anomalously in regard to fluorides ― they do not wet their surface and are inert when in contact with them. This is attributable to the formation of an intermediate gaseous phase (a volatile fluoride) which separates the liquid metal from the solid surface. Effective use can be made of this phenomenon to develop refractories (crucibles, containers, jackets, etc.) for use in the isothermal melting, homogenization, and casting of alloys that contain Ti, Zr, Hf, and V.