**Solid electrolytes (GDC, BE)**

Microstructure of sintered pellets of solid electrolytes was studied by SEM. Figs. 7. and 8 present typical microstructure of samples after radiation-thermal treatment and microwave heating. Both electrolytes demonstrate a high density without visible cracks. Some closed porosity in observed in BYS (Fig. 8).

The average grain size of GDC oxide after RTS (0.2-0.5 μm) seems bigger than domains of GDC sintered by microwave heating (0.1-0.4 μm). This fact can be explained by very fast diffusion in the solid under e-beam. Thus, microwave heating stimulates local radiation absorption, and only part of this energy dissipates into heat that stimulates grain growth. Moreover, RTS was held for 150 min vs 90 min of MH. For conventional sintering it is a common knowledge that increasing sintering time increases grain size.

### **Cathode materials (LFN-GDC, LFC-GDC)**

Sintering of bulk cathode composites was studied using radiation-thermal sintering and conventional heating techniques. In Figs. 9 and 10 values of density estimated by Archimedes method are presented in dependence on sintering temperature and duration of radiation treatment.

Advanced Sintering Techniques in Design of

50

keeping at 1300 C for 5 hours.

high-temperature treatments.

60

70

% theoretical density

80

90

100

60% at 900 C to 95% at 1200 C.

Planar IT SOFC and Supported Oxygen Separation Membranes 131

As follow from Fig.10, duration of radiation-thermal treatment has a small effect on the real density of sample. In fact, after 60 min of RTS no significant increase of density was observed. On the contrary, the temperature strongly affects the density increasing it from

> 900 C 1000 C 1100 C

0 20 40 60 80 100 120 140 160 180

It is worth noting that all samples sintered by RTS have a high mechanical strength even after RTS at 900C. This fact is obviously explained by formation of crystal-type contacts in the bulk of composite. Nothing of this kind was observed by conventional sintering at the same temperatures and sintering time. Another important fact consists in the level of theoretical density: by using RTS technique we obtained 95 % of theoretical density at 1200 C and 60 min treatment, while by conventional sintering it can be achieved only after

The internal microstructure of sintered cathodic composite was studied by SEM images of cross-sections in back-scattered electrons (Fig. 11). Dark regions in this image correspond to perovskite-type phase, and gray to GDC. After sintering, interpenetrating structures of perovskite phase (electronic conductor) and fluorite-type GDC (ionic conductor) are observed. LFN-GDC sintered by conventional heating is characterizes by residual porosity (typical size of pores 0.5-1 μm) due to shrinkage of nanosized particles. The same features of microstructure were observed for LFC-GDC composite. Hence, cathodic composites based on lanthanum ferrites/cobaltite with GDC are expected to demonstrate the same features during radiation-thermal sintering: fast shrinkage under e-beam, formation of matrix even at moderate temperatures, which prevents diffusion of La cations into electrolyte typical to

Fig. 10. Effect of sintering time on the density of cathode LFN-GDC composite.

Time, min

Fig. 7. SEM images demonstrating bulk (cross-section) structure of GDC after radiationthermal sintering (a) and after microwave heating (b).

Fig. 8. SEM image demonstrating internal structure of BYS after microwave heating at 900C.

Fig. 9. Influence of temperature on density of LFN-GDC cathode composite.

Fig. 7. SEM images demonstrating bulk (cross-section) structure of GDC after radiation-

Fig. 8. SEM image demonstrating internal structure of BYS after microwave heating at 900C.

900 1000 1100 1200

C

Temperature, 0

Fig. 9. Influence of temperature on density of LFN-GDC cathode composite.

thermal sintering (a) and after microwave heating (b).

60

70

80

% theoretical density

90

100

 LFN-GDC after RTS (120 min) As follow from Fig.10, duration of radiation-thermal treatment has a small effect on the real density of sample. In fact, after 60 min of RTS no significant increase of density was observed. On the contrary, the temperature strongly affects the density increasing it from 60% at 900 C to 95% at 1200 C.

Fig. 10. Effect of sintering time on the density of cathode LFN-GDC composite.

It is worth noting that all samples sintered by RTS have a high mechanical strength even after RTS at 900C. This fact is obviously explained by formation of crystal-type contacts in the bulk of composite. Nothing of this kind was observed by conventional sintering at the same temperatures and sintering time. Another important fact consists in the level of theoretical density: by using RTS technique we obtained 95 % of theoretical density at 1200 C and 60 min treatment, while by conventional sintering it can be achieved only after keeping at 1300 C for 5 hours.

The internal microstructure of sintered cathodic composite was studied by SEM images of cross-sections in back-scattered electrons (Fig. 11). Dark regions in this image correspond to perovskite-type phase, and gray to GDC. After sintering, interpenetrating structures of perovskite phase (electronic conductor) and fluorite-type GDC (ionic conductor) are observed. LFN-GDC sintered by conventional heating is characterizes by residual porosity (typical size of pores 0.5-1 μm) due to shrinkage of nanosized particles. The same features of microstructure were observed for LFC-GDC composite. Hence, cathodic composites based on lanthanum ferrites/cobaltite with GDC are expected to demonstrate the same features during radiation-thermal sintering: fast shrinkage under e-beam, formation of matrix even at moderate temperatures, which prevents diffusion of La cations into electrolyte typical to high-temperature treatments.

Advanced Sintering Techniques in Design of

structure, 1200C.

Planar IT SOFC and Supported Oxygen Separation Membranes 133

a b

c d Fig. 12. SEM images of thin (10 microns) layers of electrolytes supported on anodic substrate

a b

Fig. 13. SEM image demonstrating typical structure of LFN-GDC (a) and LaBiMn –BiEr layers (b) on Ni-Al foam-based substrates after radiation-thermal sintering at 900C.

NiO/YSZ/Ni-Al foam and sintered by radiation-thermal treatment at different

temperatures. a- GDC, 1200C; b - BE , 900C, c-BYS, 900C, d- La9SrSi6O26.5 with apatite

Fig. 11. Internal microstructure by SEM images in back-scattered electrons of LFN-GDC nanocomposite, CH 1300 C.
