**2.3 Sintering techniques**

124 Sintering of Ceramics – New Emerging Techniques

materials was elucidated. Experimental samples of button-size fuel cells and oxygen separation membranes were manufactured using advanced sintering techniques and

Nanocrystalline complex oxides with ionic conductivity (fluorite-type electrolytes GDC, YSZ, δ-Bi2O3 stabilized by Er or Y+Sm) and mixed ionic-electronic conductivity (rare-earth manganites, nickelates, ferrites, cobaltites and their solid solutions including those doped by Sr and/or Bi) were synthesized by modified polymerized polyester citric acid-ethylene glycol precursors (Pechini) and mechanical activation routes. Synthesis procedures and structural features of these complex oxides are described in details elsewhere (Kharlamova et al., 2011; Sadykov et al., 2011). Nanocomposites were prepared by ultrasonic dispersion of the mixture of powders in isopropanol (solvent) using a T25 ULTRA-TURRAX (IKA, Germany) homogenizer with addition of polyvinyl butyral. Detailed compositions of complex oxide and their composites prepared for sintering are summarized in Table 1.

Materials Abbreviation Chemical composition Geometry Sintering

Ce0.9Gd0.1O2-δ (50 wt.%)

Ce0.9Gd0.1O2-δ (50 wt.%)

LFC LaFe0.5Co0.5O3-δ Pellets CH

YSZ Y0.08Zr0.92O2-δ Pellets MH BE Bi0.5Er0.5O2-<sup>δ</sup> Pellets CH BYS Bi1.5Y0.3Sm0.2O2-<sup>δ</sup> Pellets CH, MH

Pellets were uniaxially pressed from powders under 5.5 t/cm2. As a porous metal substrate for composite anode or cathode, a unique type of macroporous planar Ni-Al foam substrate with a high electric and thermal conductivity, thermal stability and corrosion resistance was used (Smorygo et al., 2008; Sadykov et al. 2010). Along with these metal substrates, traditional NiO/YSZ planar anode substrates covered by thin layers of YSZ electrolyte were used for supporting cathode layers (Sadykov et al, 2009, 2011). Functional layers were

Cathode LFN LaFe0.7Ni0.3O3-δ Pellets CH

LFN-GDC LaFe0.7Ni0.3O3-δ (50 wt.%)-

LFC-GDC LaFe0.5Co0.5O3-δ (50 wt.%)-

Electrolyte GDC Ce0.9Gd0.1O2-δ Pellets

(40%)

supported by slip casting or screen-printing on the support surface.

\* CH- conventional heating, MH- microwave heating, RTS-radiation-thermal sintering

Anode NiO/YSZ NiO (60%)-Y0.16Zr0.84O2-<sup>δ</sup>

Тable 1. Compositions and samples geometry.

**2.2 Samples preparation for sintering** 

techniques\*

CH, RTS, MH

CH, RTS CH

Pellets CH, RTS

Pellets CH, RTS

Layer

Pellets, Foambased

successfully tested showing promising performance.

**2. Experimental** 

Cathode composite

**2.1 Powder synthesis** 

Functional layers and uniaxially pressed pellets were sintered by different techniques: conventional heating (CH) in the furnace at temperatures up to 1300C (nanocomposites) or 1400C (electrolytes) with or without sintering aids (Bi or Ag nitrates, etc) in different gas atmospheres (air, Ar, etc); microwave heating (MH) or radiation-thermal sintering (RTS) under electron beam action.

For conventional heating, a high-temperature oven equipped with a quartz reactor specially designed for heating in the argon flow was used.

MH was carried out using a system based on gyrotron with frequency 24 GHz specially designed for heating of materials. Samples were heated by the focused radiation (power 0.5- 1.5 kW) up to 1000-1200C with heating rate 50/min followed by dwelling at the final temperature for 30 min and then cooling to room temperature.

RTS was carried out on an ILU-6 accelerator that gives electron pulses with a high (2.4 MeV) energy. Temperature was varied in range of 900-1200 C (heating rate 30-40 /min) by changing the frequency in the range of 8-20 Hz. Time of treatment was varied in the range of 10-240 min.
