Method for preparing a thin ceramic material with controlled surface porosity gradient, and resulting ceramic material

Abstract

A method for preparing a thin ceramic material with a continuous controlled surface porosity gradient is disclosed as well as its use for producing electrochemical cells that conduct by oxide ions. The thin ceramic material is characterized by a continuous variation in porosity from 0% to about 80% of small thicknesses.

1 - 34 . (canceled) 
     
     
         35 . A method for preparing a thin ceramic material with a controlled surface porosity gradient, comprising:
 a) a step (P) of preparing the porous pore-forming substrate of a controlled thickness;   b) a step (Q) of preparing a ceramic suspension in a solvent;   c) a step (A) of infiltrating said porous pore-forming substrate of a controlled thickness with said suspension of a ceramic material;   d) a step (B) of evaporating said solvent, in order to form a pore former/solid ceramic composite structure (S);   e) a step (B′) of cutting said composite structure (S) into structure elements (s);   f) a step (E) of forming an assembly from the two elements (s 1 ) and (s 2 ) obtained in step (B′), wherein said elements are stacked back to back with their dense faces being adjacent;   g) a step of thermocompression;   h) a step (C) of debinding; and   i) a step (D) of sintering.   
     
     
         36 . The method as defined in  claim 35 , in which steps (C) and (D) are carried out as a single step (C′). 
     
     
         37 . The method as defined in  claim 35 , in which the preparation of the solid porous pore-forming substrate of step (P) comprises:
 a) a step (P a ) of preparing a suspension of one or more solid pore formers in a solvent, if necessary in the presence of binders, plasticizers and/or dispersants, and with, if so desired, the addition, in a small proportion, of ceramic particles;   b) a step (P b ) of casting said suspension formed in step (P a ) on a flat surface; and   c) a step (P s ) of evaporating said solvent.   
     
     
         38 . The method as defined in  claim 37 , in which step (P b ) is preceded by a step (P d ) of deagglomerating the pore-forming particles in said suspension formed in step (P a ). 
     
     
         39 . The method as defined in  claim 38 , in which step (P b ) is followed by a step (P e ) of deaerating said suspension. 
     
     
         40 . The method as defined in  claim 35 , in which the preparation of the ceramic suspension of step (Q) comprises:
 a) a step (Q a ) of preparing a suspension of solid ceramic particles in a solvent, in the presence of a dispersant; and   b) a step (Q b ) of adding a binder and optionally a plasticizer to the suspension prepared in step (Q a ).   
     
     
         41 . The method as defined in  claim 40 , in which step (Q b ) is preceded by a step (Q c ) of deagglomerating the suspension prepared in step (Q b ). 
     
     
         42 . The method as defined in  claim 40 , in which step (Q b ) is followed by a step (Q d ) of deaerating said suspension. 
     
     
         43 . The method as defined in  claim 41 , in which step (Q b ) is followed by a step (Q d ) of deaerating said suspension. 
     
     
         44 . The method as defined in  claim 35 , wherein the ceramic material making up the ceramic suspension is chosen from doped ceramic oxides which, at the operating temperature, are in the form of a crystal lattice having oxide ion vacancies. 
     
     
         45 . The method as defined in  claim 35 , wherein said crystal lattice is in the form of a cubic phase, fluorite phase, Aurivillius-type perovskite phase, brown-millerite phase or pyrochlore phase. 
     
     
         46 . A composition obtained by the method as defined in  claim 35 . 
     
     
         47 . The method as defined in  claim 35 , in which the composite structure (S) resulting from step (B) undergoes a step (B′) of cutting into structure elements (s). 
     
     
         48 . The method as defined in  claim 47 , in which the elements (s) obtained are of identical shape and size. 
     
     
         49 . The method as defined in  claim 47 , in which two elements (s 1 ) and (s 2 ) obtained in step (B′) are stacked back to back, their dense faces being adjacent, in order to form an assembly (E) which then undergoes thermocompression followed by steps (C) then step (D), or step (C′). 
     
     
         50 . A solid-state electrolyte composition and mixed ionic/electronic conductor composition which are obtained by the method as defined in  claim 49 . 
     
     
         51 . An electrochemical cell comprising the solid-state electrolyte as defined in  claim 50 . 
     
     
         52 . A mixed ionically/electronically conducting ceramic membrane, comprising a mixed ionic/electronic conductor as defined in  claim 50 . 
     
     
         53 . The process of extracting extract oxygen from a gaseous mixture containing oxygen utilizing a electrolyte produced by the method as defined in  claim 49 . 
     
     
         54 . The process of analyzing for the presence of oxygen in a gaseous atmosphere utilizing said solid-state electrolyte obtained by the method as defined in  claim 49 . 
     
     
         55 . A method for producing ultrapure oxygen, consisting in separating oxygen from air by ionic conduction through an electrochemical cell as defined in  claim 51 . 
     
     
         56 . A method for eliminating oxygen from a gaseous atmosphere in which applications requiring oxygen-free atmospheres are carried out, consisting in separating oxygen from said atmosphere by ionic conduction through an electrochemical cell as defined in  claim 51 . 
     
     
         57 . A method for producing thermal and electrical energy within a solid-state fuel cell, by the reaction of oxygen with hydrogen, wherein said oxygen is obtained by separating it from air, by mixed ionic/electronic conduction through a ceramic membrane as defined in  claim 52 . 
     
     
         58 . A method for producing syngas by the catalytic reaction of natural gas with steam and oxygen, wherein said oxygen is obtained by separating it from air, by mixed ionic/electronic conduction through a ceramic membrane as defined in  claim 52 . 
     
     
         59 . A method for producing ultrapure oxygen, wherein said oxygen is separated from air by mixed ionic/electronic conduction through a ceramic membrane as defined in  claim 52 . 
     
     
         60 . An industrial process for synthesizing an organic compound, comprising at least one oxidation step using gaseous oxygen, wherein said oxygen is obtained by separating it from air, by mixed ionic/electronic conduction through a ceramic membrane as defined in  claim 52 .