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High temperature stability of Ba0.5Sr0.5Co0.8Fe0.2O3-d and La0.6Sr0.4Co1-yFeyO3-d oxygen separation perosvkitic membranes

pubblicazioni - Poster

High temperature stability of Ba0.5Sr0.5Co0.8Fe0.2O3-d and La0.6Sr0.4Co1-yFeyO3-d oxygen separation perosvkitic membranes

Sono riassunti i principali risultati delle attività di caratterizzazione di membrane per la separazione dell’ossigeno ad alta temperatura.

Among the materials developed as membranes for high temperature oxygen separation (for oxycombustion or coal gasification processes) the non-stoichiometric perovskitic compounds (ABO3-δ) are very promising due to their high permeation [1-3].

In such compounds, oxygen transport is diffusive in the bulk through the cationic vacancies; the cubic structure is the most favourable as the vacancies are randomly distributed in the lattice, increasing the transport properties.
This is the case of the strontium cobalt-ferrite, Sr(Co,Fe)O3-δ (SCF) at high temperature (around 1000°C), but brownmillerite formation causes structural instability in the temperature range 700-900°C.
To overcome such a problem, the partial substitution of Sr (2+) with different anions, such as La (3+) and Ba (2+) is widely studied and under continuous development [3]. Lanthanum presence generates a charge unbalance, locally compensated by oxygen vacancies formation; the rombohedral structure of (La,Sr)(Co,Fe)O3-δ (LSCF) compounds at room temperature transforms into the desired cubic structure at a temperature in the range 700-850°C. On the other side, the partial substitution of Sr with Ba produces cubic (Ba,Sr)(Co,Fe)O3-δ (BSCF) compounds, with even better permeation properties

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