~(18)O/~(16)O isotope exchange for yttria stabilised zirconia in dry and humid oxygen

摘要

The oxygen surface kinetics and mechanism of oxygen interaction between oxygen from the gas phase and yttria-stabilised zirconia nano-sized powder have been studied by pulse O-18/O-16 isotope exchange (PIE) in dry (O-2) and humid (mixture O-2 + H2O with pH(2)O = 2.6 kPa at T = 22 degrees C) oxygen atmospheres in comparison with micro-sized powder. Dependences of the heterogeneous oxygen exchange rate (r(H)) in the temperature range from 550 to 900 degrees C, and oxygen partial pressure range in the carrier gas and pulses of 5-19% have been obtained. It has been established that the presence of water causes a decrease in the heterogeneous oxygen exchange rate due to the presence of strongly bound hydroxyl groups in the nanopores of the sample. Differences between the mechanisms of isotopic exchange for dry and humid atmospheres have been found in this temperature range (550-700 degrees C). The observed differences are associated with the interaction of the gas phase and hydroxyls in the adsorbed layer of the oxide. An original method for the separation of the contributions of three types of oxygen exchange for dry and humid atmospheres has been proposed. (C) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.