Three-Dimensional EBSD Analysis of YSZ, NiO-YSZ and Ni-Alloy
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Three-Dimensional EBSD Analysis of YSZ, NiO-YSZ and Ni-Alloy Laxmikant V. Saraf EMSL, Pacific Northwest National Laboratory, Richland WA 99352 USA. ABSTRACT In this report, a method is discussed to perform successive milling on yttria-stabilized zirconia (YSZ), NiO-YSZ and Ni-alloy at the intervals of 85 nm 50 nm and 100 nm, respectively using a focused ion beam (FIB) followed by electron backscatter diffraction (EBSD) analysis on each slice. The EBSD data is then reconstructed to generate 3D volume. The 3D-EBSD band quality data is superimposed on inverse pole figure (IPF) grain orientation analysis to get a correlation with quality of band indexing. For the NiO-YSZ case, grain orientations and band quality factors were matched for grains ~250 nm diameters producing a high resolution 3D-EBSD data. For this case, a pore space in 3D volume was visible due to nanocrystalline NiO-YSZ grain network. The advantages of 3D EBSD are discussed in the context of its applications to SOFC research community. INTRODUCTION As shown in the schematics of Figure 1, yttria-stabilized zirconia (YSZ), NiO-YSZ and Ni-alloy are frequently used in solid oxide fuel cells (SOFC) as electrolyte, anode, metal interconnects and seals [1-4]. Surface microstructure analysis of these materials using electron backscatter diffraction (EBSD) has many advantages such as combining high resolution microstructure with imaging to provide site specific information for phase, chemistry and morphology. The information needs to be extended to three dimensions due to limitations in 2D analysis with regard to pore space volume, triple phase boundary length, density and cracks formation. Especially in the case of SOFC, all of these parameters are crucial to determine the cell efficiency. Because EBSD is a surface specific (10-50 nm from surface) analysis technique, a systematic combination of 2D-EBSD data from varying depths into reconstruction in 3D volume brings us an opportunity to extend site-specific micro-texture analysis in the third dimension. The data can strongly aid during SOFC analyses like surface reactivity orientation correlation, pore space fuel conversion relation and accurate measurement of triple phase boundary length which are catalytically active for fuel to ion/electron conversion. In this report, a method is discussed to analyze 3D-EBSD data from YSZ, NiO-YSZ and Ni-alloy. EXPERIMENT Samples Preparation The YSZ sample preparation for EBSD analysis was done by pressing 8 mol% (Y2O3) doped ZrO2 powder (from Tosoh Corp. Japan) uniaxially at 4500 kgs and annealed at 1773 K for 5 hours in air to get 25.4 mm diameter and 3 mm thick dense pellet. YSZ pellets were further mechanically polished down to ~1 µm surface smoothness. After polishing, acetone and alcohol rinsed pellets were dried at 773 K in air for 2 hours. For NiO-YSZ, polycrystalline pellets of
Seal & interconnects isolators
Ni‐alloy
e‐
e‐
H2 in
Air in e‐
e‐ O‐ ‐ O‐ ‐
H2
O2
H+ H2 & H2O out
Air out Anode
(NiO‐YSZ)
Electrolyte
Cathode
(YSZ)
Figure 1. Schematics of S
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