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Rajalekshmi Chockalingam, Vasantha R.W. Amarakoon, and Herbert Giesche New York State College of Ceramics at Alfred University, Alfred, NY, USA Alumina.

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Presentation on theme: "Rajalekshmi Chockalingam, Vasantha R.W. Amarakoon, and Herbert Giesche New York State College of Ceramics at Alfred University, Alfred, NY, USA Alumina."— Presentation transcript:

1 Rajalekshmi Chockalingam, Vasantha R.W. Amarakoon, and Herbert Giesche New York State College of Ceramics at Alfred University, Alfred, NY, USA Alumina / Cerium Oxide Nano-Composite Electrolyte for Solid Oxide Fuel Cell Applications NYSCC Alfred University Center for Advanced Ceramic Technology

2 NYSCC Alfred University Center for Advanced Ceramic Technology But first: “Where on earth is Alfred ?”

3 NYSCC Alfred University Center for Advanced Ceramic Technology Anode: Ni + YSZ Cathode: La 1−x Sr x MnO 3-δ Electrolyte: 8 mol% Y 2 O 3 stabilized ZrO 2 1000°C Operated at close to 1000°C. http://en.wikipedia.org/wiki/Image:Fcell_diagram_sofc.gif

4 Alternative Electrolyte Materials NYSCC Alfred University Center for Advanced Ceramic Technology For Example: Gadolinium doped Ceria Ce 0.8 Gd 0.2 O 1.9 Leading to lower operation temp. However !!! under reducing conditions: Ce +IV → Ce +III electronic conduction. Idea !!! Electron Trapping Interfaces. S.M. Haile, “Fuel cell materials and components,” Acta materialia, 51, 5981-6000 (2003)

5 “Electron Trapping” NYSCC Alfred University Center for Advanced Ceramic Technology

6 So, how do we make such a microstructure? NYSCC Alfred University Center for Advanced Ceramic Technology Coated Nano-particles. Densify/sinter and retain microstructure. (microwave sintering; fast & uniform)

7 Center for Advanced Ceramic Technology Use two suspensions of particles with opposite charge. Zeta-potential (pH) Surfactant adsorption Porous coating; weak adhesion forces; requires large difference in particle size Heterocoagulation + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + NYSCC Alfred University

8 Center for Advanced Ceramic Technology Alfred University Precipitate coating material onto seed particles. Essentially “any” precipitation reaction can be used. As long as it is a “controlled” (slow) precipitation Dense and uniform coating Heteronucleation

9 Center for Advanced Ceramic Technology Silica-Yttria: Schematic Examples of Microstructures NYSCC Alfred University Example

10 Center for Advanced Ceramic Technology Silica spheres coated with yttria. Heteronucleation Example NYSCC Alfred University

11 Center for Advanced Ceramic Technology Excess silica cores remain after phase transformation and sintering. Visualized by etching with HF. Heteronucleation Example cont. NYSCC Alfred University

12 Center for Advanced Ceramic Technology Alfred University Alumina core (seed) Cobalt and Manganese surface layer; acceptor states at the interface Gadolinium doped Ceria (50 to 100 nm) oxygen-ion-conductor; ‘continuous phase’ Microwave sintering to retain the proposed microstructure Schematic of the “new” nano-composite electrolyte.

13 Center for Advanced Ceramic Technology NYSCC Alfred University Al(OC 4 H 9 ) 3 H 2 O (75°C) Hydrolysis under vigorous stirring for 30 min Peptization with HNO 3 & Aging at 95°C for 5 days Al 2 O 3 SOL Mn (NO 3 ) 2 6H 2 O + H 2 O Co (NO 3 ) 2 6H 2 O + H 2 O NH 4 OH + H 2 O Mn, Co coated Al 2 O 3 Sol Stirr at 90°C for 4 hrs & Age 24 hrs Synthesis of Mn, Co doped Al 2 O 3 Sol

14 Center for Advanced Ceramic Technology NYSCC Alfred University Coating of Gd doped CeO 2 on Al 2 O 3 Sol Gd(NO 3 ) 3 6H 2 O +H 2 O Aging at RT for 24 hours Dry and heat Treatment Mn, Co coated Al 2 O 3 Sol Forming and sintering Gd 0.2 Ce 0.8 O 1.9 coated on Mn, Co coated Al 2 O 3 Sol NH 4 OH + H 2 O Vigorous stirring at 93°C for 6 hours Ce(NO 3 ) 3.6H 2 O +H 2 O

15 Microwave Sintering Set up Figure (A) 2.45 GHz MW Furnace and Figure (B) Sample set up with alumina insulation box and Thermocouple. AB NYSCC Alfred University Center for Advanced Ceramic Technology

16 Sintering: Temperature Profile NYSCC Alfred University Center for Advanced Ceramic Technology

17 XRD Results for Gd 0.2 Ce 0.8 O 1.9 - 0.34% Mn- 0.34% Co-Al 2 O 3 NYSCC Alfred University Center for Advanced Ceramic Technology ♥ matches Gd 0.2 Ce 0.8 O 1.9

18 Center for Advanced Ceramic Technology SEM Micrographs: Al 2 O 3 - 0.34% Mn,Co-Gd 0.2 Ce 0.8 O 1.9 MW1250C-40min 500nm CONV-1350C-5hr NYSCC Alfred University

19 Center for Advanced Ceramic Technology Microwave sintering Conventional sintering

20 NYSCC Alfred University Center for Advanced Ceramic Technology Impedance Spectroscopy in Air (‘Ionic Conductivity’)

21 NYSCC Alfred University Center for Advanced Ceramic Technology Electrical Conductivity as a Function of Oxygen Partial Pressure

22 NYSCC Alfred University Center for Advanced Ceramic Technology Electrical Conductivity as a Function of Oxygen Partial Pressure

23 Center for Advanced Ceramic Technology Coated powders lead to unique microstructure. Microwave sintering is substantially faster. Submicron grain size can be retained Increased hardness. Electron trapping states at the alumina-ceria interface reduce electronic conductivity. Al 2 O 3 inclusions have no major effect on ionic-conductivity. Conclusions NYSCC Alfred University Better control of coating - thickness and uniformity. Test of other material combinations. Measure oxygen conductivity ‘directly’ (transference number). Test in a ‘real’ device !!! What’s next?

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