Effect of Polymerization of Precursor Solutions on Crystallization and Morphology of Ce 0.9 Gd 0.1 O1.95 Powders
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Effect of Polymerization of Precursor Solutions on Crystallization and Morphology of Ce0.9Gd0.1O1.95 Powders Shuqiang Wang, Masanobu Awano and Kunihiro Maeda Synergy Ceramics Laboratory, Fine Ceramics Research Association, Shidami Human Science Park, Shimo-Shidami, Moriyama-ku, Nagoya 463-8687, Japan
ABSTRACT Synthesis of Ce0.9Gd0.1O1.95 (CGO) powders from polymeric precursor solutions formed by mixing nitrates and ethylene glycol at 60-85 was investigated with emphasis on the effect of the polymerization of the precursor solution on the crystallization and morphology of the derived intermediate and the resultant oxide powders. It was revealed by FTIR that the molecular structures of the polymeric precursor solution change from aldehyde or ketone groups to carboxylic acid and carboxylate groups with increasing heating time. TG-DTA analyses demonstrated the temperature shifting and the disappearance of the exothermic reactions of the derived powders with different heating times of the polymeric precursor solutions. Furthermore, it was identified by XRD, SEM and TEM that the derived powders can be changed from well crystallized organic formates of Ce1-xGdx(HCOO)3 with dendritic growth to loose agglomerated cubic CGO powders with grain sizes below 10 nm.
INTRODUCTION Rare earth oxide-doped ceria has been investigated as a promising alternative solid oxide electrolyte to replace stabilized zirconia for use in solid oxide fuel cells (SOFC) [1] and electrochemical NOx decomposition [2] at lower operation temperatures. However, difficult sintering the doped ceria to dense ceramics has been the issue for applications requiring dense electrolyte membranes even if the powders were prepared from precursor solution or by the sol-gel process [3-5]. Polymeric precursor methods, originating from the Pechini technique [6] have been employed to synthesize various mixed-cation oxide powders for electrolyte and electrode applications [7]. It is noticed that the organic precursors working as chelating agents and a resin vehicle can also produce combustion heat, which results in increased high temperature during powder calcinations making strongly agglomerated large crystallites [7] and consequently decreasing the sintering activity of the derived powders. In this paper, the crystallization and the morphology of the powders derived from precursor solutions without using citric acid, similar to those used by Chen et al. [4] and Huang et al. [5], were investigated with emphasis on the effect of the polymerization processes.
EXPERIMENTAL DETAILS The starting precursor solution was prepared by mixing Ce(NO3)3 . 6H2O and Gd(NO3)3 . 6H2O in the molar ratio Ce : Gd = 0.9 : 0.1, with 20 ml distilled water, 80 ml ethylene glycol, and 20 ml concentrated (60%) nitric acid. The as-prepared transparent solution with 0.04 mole with magnetic stirring for the final oxide was then heated on a hot plate at about 60-85 polymerization treatments. The changes in the viscosity of the solution were measured at room temperature by means of a viscometer (VM-
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