Why is carbon added during arc casting of molybdenum?

During the arc-casting process of molybdenum, carbon is added to the molybdenum powder to serve as a deoxidizing agent. Because molybdenum has an extremely high melting point, it cannot be processed into high-quality ingots using conventional methods; instead, it is melted in an electric arc, where the carbon effectively removes oxygen from the molten metal before it is cast into a water-cooled, copper mold.1