Title of Invention

A PROCESS FOR THE PREPARATION OR CERAMIC MATERIAL

Abstract A process for the preparation of a ceramic material having the general formula A<sub>x</sub>B<sub>y</sub>O<sub>2</sub>-&#948; Where A comprises Ce concentrates of bastnasite minerals, B is at least two metals selected from the group 2a, 3b and the lanthanide group of metals, and 0 < x &#8804; 1,0 < y &#8804; 1 < and -1 < &#948; < 1, Comprising the steps of dissolving the Ce concentrates; dissolving the at least two metals; mixing the thus obtained solutions; and decomposing the obtained mixed solution to form the ceramic material.
Full Text The present invention relates to a process for the preparation of a ceramic material, in particular to fluorite type ceramics for use in the preparation of ion and/or electronic conducting ceramic products, in particular for membranes useful in the separation of oxygen and oxygen containing gas mixture and for electrolytes in fuel cells and electrochemical reactors.
Fluorite ceramic materials for use in oxygen transport membranes have the general formula:
AxBy02-6
where
x A is one or more metals selected from the group of Ti, Zr, Hf, Ce and Th,
B is Sm plus at least one metal selected from the group 2a and 3b and other
lanthanides.
Classical ceramic materials for oxygen conductors are based on zirconia doped with metal such as Y, Mg and Ca.
Other ceramic oxygen conductors are based on ceria doped with metals such as Y, Sm and Gd. These materials may exhibit mixed ionic and electronic conductivity depending on oxygen partial pressure. The ceria based materials have higher coriducti vity than the zirconia based materials at temperatures below 1000°C which makes the ceria based ceramics potential for commercial oxygen separation, fuel cell application and catalysts. However, prices for pure



ceria and pure dopants are prohibitive for a more widespread commercialization. Furthermore the pure mixed oxides typically used may be very refractory and very difficult to sinter into dense ceramic components.
The invention provides a novel ceramic material having fluorite provides a novel ceramic material having fluorite structure with high oxygen ionic and electronic conductivity at high or intermediate temperatures.
Accordingly the present invention provides a process for the preparation of a ceramic material having the general formula
AxBy02-6
Where A comprises Ce concentrates of bastnasite minerals, B is at least two metals selected from the group 2a, 3b and the lanthanide group of metals, and 0 Comprising the steps of
dissolving the Ce concentrates;
dissolving the at least two metals;
mixing the thus obtained solutions; and
decomposing the obtained mixed solution to form the ceramic material.
The Ce containing fluorites may be produced by replacing pure Ce raw materials with cheaper Ce concentrates based on partly refined bastnasite minerals. As the prices for pure dopants designated B in the general formula may be prohibitive for a more widespread commercialization these components are replaced according to the present investigation with "impure" partly refined mixed oxides containing Sm, Gd and Y.

Experimental
The drip pyrolysis procedure was used to synthesize different ceramic compounds with fluorite structure. Essentially, the drip pyrolysis procedure uses stock nitrate so¬lutions where the different metal nitrates are mixed at atomic level in the required proportions according to the desired chemical formula of the required fluorite type compound.
Combustion fuel such as glucose or glycine was added to the nitrate stock solutions in order to get fuel-rich conditions.
Example 1:
Synthesis of Ceo.g(Sm/Gd)o.2O.9
Cerium concentrate of Bastansite minerals obtained form Unocal/Molycorp, and samarium/gadolinium oxide were used as raw materials. The samarium/gadolinium oxide was a cheap product also supplied by Unocal/Molycorp-Califomia and con¬tained Sm203 (57.20 wt%), Gd203 (21.52 wt%), Y2O3 (7.24 wt%), EU2O3 (2.28 wt%) and trace amounts of other lanthanide"s (Tb, Er, Ho, Yb, Ce, Lu, Nd) and loss of ig¬nition of 0.5i wt%.
The samarium/gadolinium oxide was dissolved in nitric acid (65%) in the ratio 1 to 3.7. Cerium concentrate was dissolved in nitric-acid (65%). Thereafter, the two solu¬tions were mixed together in the ratio according to the chemical formula. And, fi¬nally, combustion fuel, such as glucose or glycine, was added to the stock solutions in order to get fuel-rich conditions. This stock solution was dripped into a rotary kiln whose temperature was 600°C.
The resulting ceramic material had the following formula:
Ceo.8 (Sm/Gd)o.2O1.9
where x =0.8 y=0.2 A=Ce B=SniyGd
Powder characteristics were measured as follows. XRD analysis resulted in a cubic
structure with parameter a = 5.430 A and crystallite size
D(220)=100A Surface area
as synthesized powder (measured by nitrogen adsorption according to Brunauer, Emmett and Teller isotherm was 53.4 m"/g. Pellets were pressed and sintered at 1600°C forhours in air.

The X-Ray Diffraction PCRD) analysis showed a compound with cubic structure and crystalline parameter a = 5.424 A. Table 1 shows the profile lines obtained for a sin¬gle crystal. The values obtained for the spacings and the Miller Indices are typical of a ceramic compound with fluorite structure.

Example 2:
Conductivity Data
The ionic and electronic conductivity has been measured for different ceramic mate¬rials of the invention based on cerium oxides.
The ionic conductivity is based on physical bulk diffusion of oxygen ions through crystalline lattice and depends on temperature, envirorimental oxygen partial pres¬sure (P02) and type (and quantity) of aliovalent doping. The diffusion of the ions is due to the vacancy promoted mechanism. At high po2 values only oxygen conductiv¬ity is present. At lower po2 (especially very low oxygen partial pressures) the CeO2 -----ceramic material starts to behave as mixed ionic/electronic material. When the P02 is very low (10"-20atm) the electronic conductivity ( Ceiectr) is comparable to the ionie conductivity. The conductivity is measured in Siemens/centimeter (S/cm).
Experimental results have shown that the ionic conductivity of the ceramic materials of the invention based on Ce, Sm and Gd have a,on values between 0.1 — 0.2 S/cm at 800?C. In comparison, yttrium doped zirconia (YDZ), the classical SOFC electrolyte had a aion value of 0.05 S/cm.
The ceramic materials of the invention are suitable for eg. SOFC electrolytes due to their improved ionic conductivity. In comparison with pure Sm or Gd doping, doping with "impure" partly refined mixed SmlGd oxides found as eg. Technical products are very cheap and these oxides essentially contain Sm, Gd and little Nd together with other minor elements.


WE CLAIM:
1. A process for the preparation of a ceramic material having the general formula
AxBy02.5
Where A comprises Ce concentrates of bastnasite minerals, B is at least two metals selected from the group 2a, 3b and the lanthanide group of metals, and 0 Comprising the steps of
dissolving the Ce concentrates;
dissolving the at least two metals;
mixing the thus obtained solutions; and
decomposing the obtained mixed solution to form the ceramic material.
2. The process for the preparation of the ceramic material according to claim 1,
wherein B comprises mixed oxides of Sm, Gd and Y.
3. A process for the preparation of a ceramic material, substantially as hereinbefore described and exemplified.

Documents:

311-mas-1999 abstract-duplicate.pdf

311-mas-1999 abstract.pdf

311-mas-1999 claims-duplicate.pdf

311-mas-1999 claims.pdf

311-mas-1999 correspondence-others.pdf

311-mas-1999 correspondence-po.pdf

311-mas-1999 description (complete)-duplicate.pdf

311-mas-1999 description (complete).pdf

311-mas-1999 form-19.pdf

311-mas-1999 form-2.pdf

311-mas-1999 form-26.pdf

311-mas-1999 form-4.pdf

311-mas-1999 form-6.pdf

311-mas-1999 others document.pdf

311-mas-1999 others.pdf


Patent Number 214405
Indian Patent Application Number 311/MAS/1999
PG Journal Number 13/2008
Publication Date 31-Mar-2008
Grant Date 12-Feb-2008
Date of Filing 17-Mar-1999
Name of Patentee HALDOR TOPSOE A/S
Applicant Address NYMOLLEVEJ 55, DK-2800 LYNGBY,
Inventors:
# Inventor's Name Inventor's Address
1 PETRU GORDES VIBEMOSEN 21, DK-2670 GREVE,
PCT International Classification Number C04B 035/50
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 60/080, 210 1998-03-31 U.S.A.