The rate of vaporization of tungsten in argon

The vaporization kinetics of thin tungsten wires has been measured under natural convection conditions in high-purity argon. The rate was determined as a function of argon pressure and filament temperature in the range between 80 and 300 mm and 2850 and 3150 K. The vaporization rate is exponentially related to temperature with an activation energy of approximately 190 kcal/mole and inversely proportional to total pressure to the 0.87 power. The activation energy predicted by stagnant-film mass transfer theory is 202.5 kcal/mole, while the theoretically predicted inverse pressure dependence is 0.90. The rate was also sensitive to reactive impurities in the argon; thus,in situ, purification of the atmosphere was required.