Evaporation Technique for Highly Refractory Substances

Platinum, boron, molybdenum, quartz and other substances have been evaporated in vacuum from a crucible heated by bombardment with electrons at 4000 volts from a tungsten filament. A small pure graphite crucible was heated to its melting point about 3500°C by 100 milliamperes of electron current. Most elements will alloy with a tantalum or molybdenum crucible so a graphite cup is usually preferable. Low melting point substances which would easily alloy with a tungsten filament can be readily handled by this method, which has been used in the preparation of x-ray target surfaces, small mirrors and absorbing films.