Doped Ceria Powders Research Articles

Preparation of samaria-doped ceria for solid-oxide fuel cell electrolyte by a modified sol-gel method

Samaria-doped ceria powders were prepared by the sol-gel method with different processes. The characteristics of the sample were investigated by particle size distribution, X-ray diffraction, crystallite size, and density analyses. A modified process of the sol-gel method was proposed in this work. It involves treating the gel with high-carbon (long chain, high boiling point) alcohol. It yields near-completely soft-agglomerated nanocrystalline powders which are easily sintered in air to yield near-fully relative density at 1300°C, which is significantly lower than temperatures of 1400–1500°C required by the doped-ceria powder prepared via the previous processes of the sol-gel method.

Characterisation of Doped Ceria Powders Prepared by wet Chemical Methods

Characterisation of Doped Ceria Powders Prepared by wet Chemical Methods

Oxalate coprecipitation of doped ceria powder for tape casting

Twenty cation per cent yttria doped ceria Ce 0.8Y 0.2O 1.9 was prepared by an optimised oxalate coprecipitation route to give fine sinterable powder. This was formulated into slurries for tape casting of the doped ceria solid electrolyte used in solid oxide fuel cells. Prior dry milling of the powder was found to be most effective to further reduce the average agglomerate size, which allowed to sinter dense membranes at 1400°C for 2 h, among the best results obtained so far for tape cast doped ceria. Ball milling of the powder, composition and viscosity of the slurry as well as sintering conditions of different tapes are discussed.

Film Blowing of Ceria Electrolyte Plates

A mechanically-ground doped ceria powder with 10 mol% SmO1.5 was incorporated by high shear mixing into a polystyrene-based organic vehicle. At 45 vol.% solids loading, the suspension could be subjected to elongational flow processes and was prepared in thin film form by tubular film blowing; the manufacturing process used to make thermoplastic polymer film. This provides a potential route for the manufacture of ceramic electrolyte plates for solid oxide fuel cells for which doped ceria is a candidate material. After sintering, film thickness down to 50 μm could be achieved with relative densities >95%. The main problem with this route is in retaining flatness of films of less than 100 μm in thickness during sintering; a problem which exists whatever the particle assembly route.

Fabrication and Sintering of Fine Yttria‐Doped Ceria Powder

Yttria–doped ceria powder was prepared from oxalate precursors. The oxalate coprecipitation bath parameters were closely monitored and found to influence the sintering behavior of the subsequently obtained oxide powders strongly. The use of concentrated (Ce,Y) metal nitrate solutions and dilute neutralized oxalic acid for coprecipitation were identified as the most–important parameters. Following calcination at 700°C, compacts of such powders were sintered to high density (98%) at 1400°C (4 h). Ball milling of the powder further reduced the sintering temperature. Dry milling, for tape–casting applications of the powder in particular, was more effective than wet milling. Tape–cast membranes were fired at 1400°C (2 h), with resulting densities of 98%.

Preparation of Doped Ceria Powder

The alleged poor sinterability of (doped) ceria was studied for the application as a fuel cell solid electrolyte, and a solution has been proposed. Yttria doped ceria (YDC) powder Ce{sub 0.667}Y{sub 0.333}O{sub 1.833} was prepared by oxalate coprecipitation through addition of a concentrated yttrium-cerium nitrate solution to a dilute aqueous on of a concentrated oxalic acid solution at neutral pH. The precipitate was washed with alcohol and calcined at 700 C. Coprecipitation conditions were critical for the quality of the resulting oxide powder, of which the average particle size was a key parameter. Compacted into pellets, relative densities attained >95% and >98% of theoretical after firing for 4 hours at 1,300 C and 1,500 C respectively. Sample ``embedding`` with YDC powder further improved the final density. Standard conductivity behavior of the samples was observed. The powder could equally be tape cast and sintered to dense films.