MEASUREMENT OF OXIDATION REDUCTION KINETICS TO 2100-DEGREES-C USING NONCONTACT SOLID-STATE ELECTROLYTES

A technique for in situ measurement of oxidation kinetics and hydrogen production rates has been developed and tested in flowing mixtures of H2O/H2/Ar at temperatures up to 2100-degrees-C. The rate of oxidation or reduction of a specimen is calculated from the difference in oxygen content of the flowing gas, as measured by solid-state oxygen sensors at locations upstream and downstream from the specimen. No physical contact is required with the specimen and the temperature of the sample can be much higher than the temperature of the oxygen sensors. Limitations of this technique and uncertainties in kinetic data are described. Below 1700-degrees-C, a 10% uncertainty is typical for oxidation rates in the range 10(-5) to 10(-8) mol s-1. At higher temperatures, up to 2100-degrees-C, oxidation/reduction reactions with materials in the hot zone of the furnace must be considered and discounted when oxidation rates are calculated. The experimental apparatus is described and oxidation rate calculations are outlined for reaction in H2O/H2/Ar mixtures. The methodology can be extended to other gas mixtures including CO2/CO and possibly SO2/S2. The technique was initially developed as a tool for measuring oxidation rates of uranium dioxide in H2O/H2 mixtures, and experimental results are presented over the temperature range 1200-2000-degrees-C.