Measurement of oxygen flux as a function of oxygen activity for selected ceramic materials.

摘要

or materials that possess an ionic conductivity that is dependent upon the oxygen activity, such as those used for gas separation membranes, it is difficult to relate the oxygen flux generated by a material under an oxygen chemical potential gradient to the actual ionic conductivity values. It is possible to determine average values for the ionic conductivity or to indirectly measure it at a single oxygen activity using some electrical and thermodynamic measurements. In real gas separation systems, however, it would be beneficial to use actual oxygen flux measurements when determining the oxygen activity dependence of the ionic conductivity. This measurement would be a more direct approach than others and would be performed under the actual conditions that a material would be exposed to in a real system. When making these measurements of the oxygen flux, however, it is important to consider the influence of adding oxygen into the reducing gas stream. This additional oxygen, which may arise from a leak in the seal or delivery systems or due to the oxygen flux itself, can shift the oxygen activity of the reducing gas and limit the oxygen flux. A method for calculating the ionic conductivity as a function of oxygen activity has been developed. This method requires that the oxygen flux be measured as the oxygen activity is systematically changed on one side of the oxygen chemical potential gradient. Corrections can be made to the oxygen flux for leaks into the system and also for the shift in the oxygen chemical potential due to the addition of oxygen into the reducing gas. This method was used to determine the ionic conductivity of