Recently a customer was having some process issues with E-Beam Evaporation of Molybdenum:
Molybdenum has a vapor pressure of 10-8 at 1592 C and 10-4 at 2117 C. Molybdenum does melt, it does not sublimate. It does not specifically require a crucible liner and is an excellent E-beam evaporation material. You may be forming molybdenum carbide with your carbon crucible liner. The resultant films of molybdenum are smooth and hard. However, care must be taken to carefully outgas the material while heating the charge up to temperature. Use slow rise times and extended soak times.
You should raster your beam in a figure 8 pattern in as broad a pattern as your E-beam hearth will allow. I wouldn’t expect much of an evaporation rate below the liquidus since molybdenum does not sublimate from the solid state. The size of the starting pellets in the charge are of little significance since they will melt and the liquid will form a solid cone upon cooling after the initial run.
