A SOLID-STATE EMF METHOD TO DETERMINE EQUILIBRIUM OXYGEN PARTIAL PRESSURES OF SLOW REACTING CHEMICAL-SYSTEMS AT HIGH-TEMPERATURES

• In solid state emf measurements on sluggish systems, difficulties to achieve stable and reproducible values have been encountered. There are many indications that these problems are owing to the small, but obviously not negligible, transport of oxygen through the electrolyte. In the present work, an improved galvanic cell arrangement, here called the "zero point" method, has been developed. The principles of this method are to approach zero emf for the sample cell, containing a sluggish system, by an adjustable reference gas phase, and determine the oxygen partial pressure in the reference gas phase, initially made up of a H2/CO2 mixture, by a reference cell, containing a fast reacting metal-metaloxide equilibrium system, which is unaffected by the oxygen permeation. The following equilibrium, with a recognized slow reaction rate, was chosen as a test system to demonstrate the "zero point" method Co(s) + Cr2O3 (s) + 1/2O2 (g) reversible CoCr2O4 (s)

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