Influence of the La6W2O15 Phase on the Properties and Integrity of La6-xWO12-?–Based Membranes

Abstract

The aim of the present work is to evaluate the influence of La₆W₂O₁₅ secondary phase on the properties and integrity of La_6-xWO_12-?–based membranes. Structural, microstructural and thermo–chemical study was carried out evidencing significant crystallographic and thermal expansion anisotropy: the reason for poor thermo–mechanical stability of La₆W₂O₁₅. Conductivity of La₆W₂O₁₅ was one to two orders of magnitude lower compared to the phase pure La_6-xWO_12-? in the range of 300 to 900 °C. The relaxation study showed that the hydration process was faster for the La₆W₂O₁₅ compared to the LWO phase, due to the higher electronic contribution to the total conductivity. Short–term stability tests in H₂ at 900 °C and in a mixture of CO₂ and CH₄ at 750 °C were conducted and material remained stable. Remarkable reactivity with NiO and YSZ at elevated temperatures was further evidenced compared to the relative inert behavior towards MgO and CGO.

Keywords: La₆W₂O₁₅, La_6-xWO_12-?, mixed protonic–electronic conductor, dense ceramic membrane, hydrogen separation.