Oxygen partial pressure control for microgravity experiments

Abstract

A system consisting of a high-temperature yttrium-stabilized zirconia (YSZ) based oxygen ion pump and potentiometric sensor enables precise measurement and control of oxygen partial pressure, pO2, at elevated temperatures within 0.2 to 10^-20 bar. <the principle of operation as well as the influence of temperature and gas buffers like H2/H2O on the pO2 is discussed. The ion pump is controlled by a microcontroller system and adjusts the oxygen partial pressure with an uncertainty of Delta-log(pO2)<0.02 and response times between 5 and 90s over the entire pO2 range. The oxygen ion pump is tested in combination with the electromagnetic levitation. Here, the surface tension of molten Ni at 1720 °C as a function of oxygen partial pressure is determined. A good agreement of this measurement with calculated value confirms the applicability of the system for high-temperature measurement and control of pO2. The developed hardware is suitable for the electromagnetic levitation facility onboard the international space station (ISS).