slide1 l.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
Sol Gel Approach: Lanthanum Silicates as a Replacement for Yttria Stabilized Zirconia (YSZ) in Solid Oxide Fuel Cell (SO PowerPoint Presentation
Download Presentation
Sol Gel Approach: Lanthanum Silicates as a Replacement for Yttria Stabilized Zirconia (YSZ) in Solid Oxide Fuel Cell (SO

Loading in 2 Seconds...

play fullscreen
1 / 17

Sol Gel Approach: Lanthanum Silicates as a Replacement for Yttria Stabilized Zirconia (YSZ) in Solid Oxide Fuel Cell (SO - PowerPoint PPT Presentation


  • 288 Views
  • Uploaded on

Sol Gel Approach: Lanthanum Silicates as a Replacement for Yttria Stabilized Zirconia (YSZ) in Solid Oxide Fuel Cell (SOFC) Electrolytes. Aminah Rumjahn Chemical Engineering and Material Science University of California, Davis. University of California, Irvine

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Sol Gel Approach: Lanthanum Silicates as a Replacement for Yttria Stabilized Zirconia (YSZ) in Solid Oxide Fuel Cell (SO' - johana


Download Now An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
slide1

Sol Gel Approach: Lanthanum Silicates as a Replacement for Yttria Stabilized Zirconia (YSZ) in Solid Oxide Fuel Cell (SOFC) Electrolytes

Aminah Rumjahn

Chemical Engineering and Material Science

University of California, Davis

University of California, Irvine

Chemical Engineering and Material Science

PI: Martha Mecartney

Graduate student: Mai Ng

outline
Outline
  • Intro to Solid Oxide Fuel Cells (SOFCs)
  • Motivation for Work and Goals
  • Background of Apatite
  • Experimental procedure
  • Data
  • Results
  • Conclusion/Future Work
sofcs
SOFCs

www.eos.polito.it/h_fuel_ing2.htm

motivation
Motivation
  • Yttria Stabilized Zirconia (YSZ) is traditional material used for electrolyte

Main disadvantage: High operating temp

Diffusion equation: D = D0exp(-Q/RT)

  • New materials must be considered
  • Good electrolyte: stable, lower operating temp, high oxygen ion conductivity
  • Apatite = lower operating temp and high oxygen ion conductivity
grain size must be small
Grain Size Must Be SMALL!
  • Studies have shown some nanocrystalline ceramics have high ionic conductivity
  • Ionic conductivity governed by grain boundaries
  • Ions in oxy-apatite travel faster in interstitial regions
  • Hypothesis is more grain boundaries = higher conductivity

Small grains  More grain boundaries

= More efficient electrolyte material

apatite
Apatite
  • A type of mineral
  • Structure
  • Hexagonal monoclinic
  • Rare earth oxy-apatites:
  • La, Ce, Gd, Sm
  • Specifically, apatite-type lanthanum silicates exhibit highest ionic conductivity

Silicate-based apatite with SiO4 tetrahedra (yellow). The calculated pathway for oxygen diffusion is shown.

*M S Islam, University of Bath

about sol gel
About Sol Gel
  • Solution chemistry based
  • Inorganic metal salts/metal organic compounds (metal alkoxides)
  • Hydrolysis and polymerization forms liquid SOL
  • Condensation forms solid GEL
  • Heat treatment  crystalline ceramics
  • Advantages
    • composition highly controllable
    • low temperatures
    • homogenous mixing
    • more freedom for applications -- coat = thin films

SOL

GEL

procedure
Procedure
  • Dissolve lanthanum nitrate hexahydrate in ethanol and acetic acid
  • Add tetraethylorthosilicate (TEOS)

 Sol

  • Dry overnight

Gel

  • Heat treatments: Decompose at 600°C for 4hrs and Calcine at 1000°C for 2hrs

Solid oxy-apatite (La9.33Si6O26)

cryomilling
Cryomilling
  • No previous studies on cryomilling of ceramics
  • Success with cryomilling of metals

Reduced grain size of Al to ~26nm*

  • Cryogenic = very low temps  liqN2(-200°C)

*F.Zhou, D.Witkin, S.R. Nutt, E.J. Lavernia, Mater. Sci. Eng. A375-377 (2004) 917-921

results xrd
Results: XRD

STANDARD

CRYOMILLED

Water Contamination!!

Secondary phase: La2SiO5

scherrer equation
Scherrer Equation

t = 0.9λ

Bcos (θB)

t = crystallite size

λ = wavelength of Cu filament (1.54Å)

B = width of peak at ½Imax

θB = angle of peak

NOT APPLICABLE FOR SIZES > 200nm

Crystallite size of standard sample:

~21nm

Crystallite size of cryomilled sample:

~14nm

results sem
Results: SEM

Standard Sol Gel

Cryomilled Sol Gel 

results sem13
Results: SEM

STANDARD

results sem14
Results: SEM

CRYOMILLED

conclusions
Conclusions
  • Fabricated apatite-type La9.33Si6O26 through sol gel route
  • Scherrer formula gives similar crystallite sizes
  • SEM shows cryomilled powders are less agglomerated

Uncertain of the effects of cryomilling!!

future work
Future Work
  • Fabrication of sintered pellets to conduct impedance spectroscopy (IS) to determine ionic conductivity of La9.33Si6O26
  • More Cryomilling!!!

Devise a better collection method to

avoid water contamination

Vary the milling time

Characterization tests

Density measurements

acknowledgements
Acknowledgements
  • Professor Martha Mecartney and Graduate student Mai Ng for their enthusiasm, guidance and support
  • Mecartney and Mumm groups
  • UC Irvine and the UROP team for the IMSURE program
  • NSF for financial support
  • Zeiss Center of Excellence for microscopy support