Addition of (a) blocking agent(s) in a ceramic membrane for clocking crystalline growth of grains during atmospheric sintering
View Patent ↗A composite material (M) comprising: at least 75% by volume of a mixed electronic conductor compound oxygen anions O<2->(C1) selected from doped ceramic compounds which, at the temperature of use, are present in the form of a crystalline network having ion oxide lattice vacancies and, more particularly, in the form of a cubic phase, a fluorite phase, a perovskite phase, of the aurivillius variety, a Brown-Millerite phase or a pyrochlore phase; and 0.01%-25% by volume of a compound (C2) which is different from compound (C1), selected from oxide-type ceramic materials, non-oxide type ceramic materials, metals, metal alloys or mixtures of said different types of material; and 0%-2.5% by volume of a compound (C 3 ) produced from at least one chemical reaction represented by the equation: xFC1+yFC2 - - - >zFC3, wherein FC1, FC2 and FC3 represent the raw formulae of compounds (C1), (C2) and (C3) and x, y and z represent rational numbers above or equal to 0. The invention also relates to a method for the preparation and use thereof as mixed conductor material for a membrane catalytic reactor used to synthesize synthetic gas by catalytic oxidation of methane or natural gas and/or as mixed conductor material for a ceramic membrane.
1. A composite (M) comprising:
a) at least 75 vol % of a mixed electronic/oxygen O 2− anionic conducting compound (C 1 ) which, at the use temperature, are in the form of a crystal lattice having oxide ion vacancies, compound (C 1 ) being a perovskite compound of a formula selected from the group consisting of:
1) La (1−x−u) Sr x Al u Fe (1−v)Ti v O 3−δ ,
2) La (1−x−u) Sr x Al u Fe (1−v) Ga v O 3−δ ,
3) La (1−x) Sr x Fe (1−v) Ti v O 3−δ ,
4) La (1−x) Sr x Ti (1−v) Fe v O 3−δ ,
5) La (1−x) Sr x Fe (1−v) Ga v O 3−δ or
6) La (1−x) Sr x FeO 3−δ
where:
0<x≦0.5;
0≦u≦0.5;
(x+u)≦0.5;
0≦y≦0.9;
0≦v≦0.9;
0≦(y+v)≦0.9; and
w is such that the structure in question is electrically neutral;
b) from at least 0.1 vol % but not more than 10 vol % of a compound (C 2 ) selected from the group consisting of magnesium oxide (MgO) and mixed barium titanium oxide (BaTiO 3 ); and
c) from 0 vol % to 2.5 vol % of a compound (C 3 ) produced from at least one chemical reaction represented by the equation:
x F C1 +y F C2 →z F C3 ,
in which equation F C1 , F C2 and F C3 represent the respective crude formulae of compounds (C 1 ), (C 2 ) and (C 3 ) and x, y and z represent rational numbers greater than or equal to 0.
2. The composite of claim 1 , in which grains of compound (C 2 ) have an equiaxed shape with a diameter ranging from 0.1 μm to 5 μm.
3. The composite of claim 1 , in which the volume fraction of compound (C 3 ) does not exceed 1.5%.
4. The composite of claim 3 , in which the volume fraction of compound (C 3 ) in the composite tends toward 0.
5. The composite of claim 1 , in which the volume fraction of compound (O 2 ) does not exceed 5%.
6. The composite of claim 1 , of formula:
La 0.6 Sr 0.4 Fe 0.9 Ga 0.1 O 3−δ , or a)
La 0.5 Sr 0.5 Fe 0.9 Ti 0.1 O 3−δ . b)
7. The composite of claim 1 , wherein compound (C 2 ) is MgO.