Sanbornite-based glass-ceramic seal for high-temperature applications

Abstract

A glass-ceramic seal for ionic transport devices such as solid oxide fuel cell stacks or oxygen transport membrane applications. Preferred embodiments of the present invention comprise glass-ceramic sealant material based on a Barium-Aluminum-Silica system, which exhibits a high enough coefficient of thermal expansion to closely match the overall CTE of a SOFC cell/stack (preferably from about 11 to 12.8 ppm/° C.), good sintering behavior, and a very low residual glass phase (which contributes to the stability of the seal).

We claim as follows: 
     
         1 . An ionic transport device component, comprising:
 a) a substrate; and   b) a sealing component coating at least a portion of the substrate surface, the sealing component including a barium silicate phase (Ba 5 Si 8 O 21  and Ba 3 Si 5 O 13 ), a hexa-celsian phase (h-BaO.Al 2 O 3 .2SiO 2  or h-BAS 2 ), and a sanbornite phase (BaO.2SiO 2  or BS 2 ), and a residual glass phase, wherein the sealing component has a residual glass phase below 10 vol % and a coefficient of thermal expansion of 11 to 12.8 ppm/° C.   
     
     
         2 . The sealing component of  claim 1 , wherein a molar ratio of SiO 2 :BaO is between about 1:1 and about 4:1. 
     
     
         3 . The sealing component of  claim 1 , wherein the molar ratio of SiO 2 :AL 2 O 3  is in a range of from 3:1 to 7:1. 
     
     
         4 . The sealing component of  claim 1 , wherein the amount of SiO 2  present is in a range of from 60.0 mol % to 65.0 mol %. 
     
     
         5 . The sealing component of  claim 1 , wherein the amount of Al 2 O 3  present is in a range of from 4.0 mol % to 10 mol %. 
     
     
         6 . The sealing component of  claim 1 , wherein the sealing component has a thickness in a range of from 1 micron to 500 microns at room temperature. 
     
     
         7 . The sealing component of  claim 1 , wherein the sealing component has a difference between a glass crystallization temperature and a glass transition temperature in a range of between about 200° C. and about 300° C. at a heating rate of about 5° C./min, between about 190° C. and about 250° C. at a heating rate of about 5° C./min, or less than about 200° C. at a heating rate of about 5° C./min. 
     
     
         8 . The sealing component of  claim 1 , wherein the sealing component has a glass stability value (K gl ) in a range of from 0.4 to 0.6. 
     
     
         9 . The sealing component of  claim 1 , wherein the ionic transport device is a solid oxide fuel cell. 
     
     
         10 . The sealing component of  claim 1 , wherein the ionic transport device is an oxygen transport membrane device. 
     
     
         11 . The sealing component of  claim 1 , wherein the sealing component has a residual glass phase of below 5%. 
     
     
         12 . The sealing component of  claim 1 , wherein the sealing component has a residual glass phase of below 2%. 
     
     
         13 . A solid oxide fuel cell, comprising:
 a) a plurality of sub-cells, each sub-cell including:
 i) a cathode in fluid communication with a source of oxygen gas; 
 ii) an anode in fluid communication with a source of a fuel gas; and 
 iii) a solid electrolyte between the cathode and the anode; and 
   b) a seal coating applied to the outer surfaces of the plurality of sub-cells and forming a hermetic seal between the cathode, anode, and electrolyte to separate the fuel gas from the oxygen gas, the seal coating including a barium silicate phase (Ba 5 Si 8 O 21  and Ba 3 Si 5 O 13 ), a hexa-celsian phase (h-BaO.Al 2 O 3 .2SiO 2  or h-BAS 2 ),and a sanbornite phase (BaO.2SiO 2  or BS 2 ), and a residual glass phase, wherein the sealing component has a residual glass phase below 10 vol % and a coefficient of thermal expansion (CTE) of 10.5 to 12.8 ppm/° C.   
     
     
         14 . The solid oxide fuel cell of  claim 13 , wherein the seal coating has a CTE that is within about 2 ppm/° C. below the CTE of the solid oxide fuel cell, or within about 1 ppm/° C. above the CTE of the solid oxide fuel cell, or within less than 1 ppm/° C. of the CTE of the solid oxide fuel cell. 
     
     
         15 . A method of applying seal coating to an ionic transport device comprising the steps of:
 a) forming a glass composition that upon heating will form a barium silicate phase (Ba 5 Si 8 O 21  and Ba 3 Si 5 O 13 ), a hexa-celsian phase (BaAl 2 SiO 8 ), a sanbornite phase (BaSi 2 O 5 ), and a residual glass phase;   b) milling the glass composition to produce a glass powder having an average particle size (d50) in a range of between about 500 nm and about 10 microns;   c) mixing the glass powder with a binder and a liquid to form a slurry;   d) coating at least a part of a surface of the ionic transport device with the slurry;   e) forming a seal coating on the ionic transport device having a crystalline structure with a residual glass phase below 10 vol % and a coefficient of thermal expansion (CTE) of 10.5 to 12.8 ppm/° C.   
     
     
         16 . The method of  claim 15 , wherein forming a seal coating on the ionic transport device having a crystalline structure comprises sintering the coated ionic transport device and heating the coated ionic transport device to form a seal coating having a crystalline structure. 
     
     
         17 . The method of  claim 15 , wherein sintering the coated ionic transport device comprises sintering the coated ionic transport device at a temperature in a range of from 800° C. to 900° C. for a time period in a range of from 2 to 4 hours. 
     
     
         18 . The method of  claim 15 , wherein heating the coated ionic transport device to form a seal coating having a crystalline structure comprises heating the coated ionic transport device to a temperature of from 900° C. to 1000° C. for a time period of from 2 to 6 hours. 
     
     
         19 . The method of  claim 18 , further comprising heating the coated ionic transport device to a temperature of about 1000° C. to about 1100° C. for a time period of from 2 to 8 hours to reduce the residual glass vol % within the seal coating. 
     
     
         20 . The method of  claim 18 , wherein heating the coated ionic transport device to a temperature of from 1000° C. to 1100° C. for a time period of from 2 to 8 hours results in a coating having a sanbornite concentration of 60 to 90%.