Effect of medium on zirconium evaporation parameters

An oil-free vacuum system was used in making a special Knudsen cell for determining Zr vapor pressure at 1300-2000deg since effects of oxide and nitride impurities caused a wide variation in published data. 95Zr tracer was used. The main impurity is O (based on neutron activation analysis etc.). The Zr-O equilibrium was studied at 1000-1824deg at 10-10-10-5 atm O. Zr vapor pressure curves are nonmonotonic exhibit singularities, and vary by 4 orders of magnitude. Corrections are made for ZrO and ZrO2 and a heat of sublimation of 40-48 kcal/mole was estimated at 1400deg