A major reason for the use of vacuum in metallurgy is to conduct processes that become possible only at low pressures. Invariably all vacuum metallurgical processes involve treatment at high temperatures, particularly when reactive and refractory metals and alloys are concerned. Such processes include reactions that lead to the preparation of compound intermediates as well as reduction and refining of refractory metals and alloys. Some of the reduction reactions and many of the refining processes occurring in these metals and alloys in a high temperature high vacuum environment involve the formation and evaporation of suboxide species besides simpler elemental as well as compound gas species. A proper use of these events for metal or alloy preparation in vacuum metallurgy process requires detailed thermodynamic analysis of the phenomena. The present paper outlines the work done in this area in the erstwhile Metallurgy Division and present Materials Processing Division. The evolution of improved and new processing schemes starting from thermodynamic analysis of vacuum metallurgical reactions is illustrated using a variety of examples of actual process development.
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