Measurements of Gas Shielding Factors for Cu, Fe, Ni
The dependence of the gas shielding factor on the pressure and the purity of the process gas is remarkable. The range can extend over several orders of magnitude .
Within the framework of the presented work, vaporization experiments using a HT- Thermobalance with UHV supply have been carried out for the elements Fe, Cu, and Ni under inert gas atmosphere and with defined oxygen partial pressures. Thereby, the oxygen partial pressure has been maintained using an oxygen ion pump. Here, an electric current between +10 and -10 mA is applied to an yttrium-doped zirconia tube operated at a temperature of 600 °C. The current flow results in oxygen being transferred into or out of the ambient gas provided to the experimental set-up with a flow rate of about 2 cm3/min. The ion pump yields accuracy in oxygen flow of 10-9 l/min and, therefore, enabled precise adjustment of pO2 within the area of interest.
The gas shielding factor not only depends on the gas purity but also on the investigated material itself. The dependency from the oxygen partial pressure for example is influenced by the partial vapor pressure of the corresponding oxides and their dissociation pressure.
 E. Fromm, METALLURGICAL TRANSACTIONS A, VOLUME 9A , DECEMBER 1978, 1835-1838