The oxygen potentials of CO₂–CO–O₂ mixtures circulated in a closed system were controlled by a feedback control system employing an oxygen sensor and an oxygen pump composed of stabilized zirconia and porous platinum electrodes.
It was confirmed that oxygen potentials in the range of −40 to −440 kJ/mol could be controlled at 1000°C with fluctuations of ±0.5 kJ/mol by means of this apparatus. The oxygen potentials could be controlled stably even in the range where stable control had not been possible in previous work.
The reliability of the controlled oxygen potentials was checked by measuring the oxidation and the reduction rate of a Ni–NiO sintered pellet heated in the closed system. The reaction rate was measured by the current passing through the oxygen pump in the steady state. The monitored oxygen potentials at which the reaction rate was zero were in agreement with the equilibrium oxygen potentials of the Ni–NiO system within an experimental error of 2 kJ/mol.