Performance of an Oxide Solid Electrolyte as a Vacuum Oxygen Partial Pressure Gauge

Abstract

Calcia stabilized zirconia of nominal composition Ca0.15Zr0.85O1.85 has been used as the electrolyte of a galvanic cell for quantitative measurements of oxygen pressure in a vacuum chamber over the range 1–10−7 Torr. The low pressure limit is determined both by permeation of oxygen through the electrolyte and interaction with active residual gases such as CO, H2, and hydrocarbons. The response of the cell to changes in oxygen pressure is dependent on the pressure and independent of the electrolyte temperature over the range 600–800 °C. The rate of approach to a steady-state following step changes in oxygen pressure over the range ≈10−7–10−4 Torr can be represented by the empirical equation (dE/dt)αΔEm, where E is the cell emf, t is time, ΔE is the departure of the emf from the steady-state value, m=1 for step increases in pressure, and m=1.5 for step decreases in pressure. The time constant for relaxation following an increase in pressure has been measured as ≈[8×10−5/PO2(Torr)] sec, where PO2 is the vacuum oxygen pressure.