Vapor Pressure and Heat of Sublimation of Tungsten

The vapor pressure of tungsten was measured by the Langmuir method in the temperature range 2600 to 3100 K using a vacuum microbalance. Four series of data gave concordant results and three of the four series gave second and third law heats of sublimation in excellent agreement. A vapor pressure equation representing the data is log P(atm) = -45385/T + 7.871, based on our mean third law heat and tabulated entropies at 2800 K. The mean third law heat of sublimation at 298.15 K is 205.52 ± 1.1 kcal mol^-1 (859.90 ± 4.6 kJ mol^-1) where the uncertainty is an overall estimated error. Rates of vaporization are about 1/2 those previously accepted for tungsten.