Novel oxygen partial pressure relaxation technique for study of oxygen exchange in nonstoichiometric oxides. The model of relaxation kinetics

Isothermal relaxation kinetics for the reduction and oxidation of SrFeO3 based perovskites

“…Previous kinetic studies have mostly focused on intrinsic oxygen transport properties at temperatures above 723 K, with a targeted application of SOFC cathodes. 17 Electrical conductivity relaxation techniques were used to determine surface exchange and diffusion coefficients for SrFeO 3 at temperatures in the range 973-1273 K. 18,19 Relaxation kinetics of SrFeO 3 have also been studied using thermogravimetric analysis, 20 and oxygen uptake in a lab scale fixed bed reactor, 21 but with both studies focused on temperatures above 723 K.…”

Oxygen Exchange in MIEC Perovskite Oxide La0.6Sr0.4Co0.2Fe0.8O3−δ: Kinetic and Equilibrium Parameters and Their Interrelation

“…The processes considered in each such reactor are divided into the surface reaction of the gas with the sample and the bulk diffusion of oxygen ions into the oxide, and the partial pressure of oxygen in the gas entering each subsequent reactor is determined by the partial pressure of oxygen in the gas mixture from the previous one. To meet these conditions, the flow is selected in such a way that the oxide in the reactor can partially restore the oxygen pressure between its initial equilibrium pressure and the oxygen pressure in the gas, that is, enter the material–gas feedback regime, corresponding to reaction conditions lying between the material-kinetic and the gas-phase limits. , In the material–kinetic limit, when the flow rates are too high, the sample will not have enough time to establish this intermediate equilibrium and the oxygen pressure in the gas above the sample will not significantly differ from the oxygen pressure in the gas. In the gas-phase limit, when the flow rate is too low, the sample will be able to keep the oxygen pressure in the reactor close to its equilibrium value, corresponding to its stoichiometry.…”

“…To study the kinetic parameters, we used the OPPR method described earlier in the study . Dense sintered cylindrical samples of a given mass and diameter were placed in a quartz reactor by the method described above.…”

“…To study the kinetic parameters, we used the OPPR method described earlier in the study. 35 Dense sintered cylindrical samples of a given mass and diameter were placed in a quartz reactor by the method described above. When operating temperatures were reached the gas mixture with an oxygen partial pressure pO 2 0 was applied to the sample (the range of partial oxygen pressures was 0.07−0.005 atm).…”

“…Thus, this study, which is one of a series of studies on the fundamental functional and applied characteristics of standard compositions of perovskite oxides, is aimed at studying the dependences of kinetic and equilibrium parameters on the nonstoichiometry δ and temperature T , and checking the presence of LFER according to the Brønsted–Evans–Polanyi principle. In addition, testing the original oxygen partial pressure relaxation and quasi equilibrium oxygen release techniques, in order to develop a research methodology, obtain reference points for further development of methods and improvement of fundamental models was included. For these purposes, lanthanum–strontium ferrite substituted in the B -sublattice with cobalt in the stoichiometric ratios La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3−δ , which is widely known as the cathode material of solid oxide fuel cells and described in detail in the literature was chosen. − …”