Preparation of Stabilized Zirconia Using A Mixture of Rare Earth Oxides as Dopant
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ADELINA P. SANTOS AND ROSANA Z. D.FERNANDES Departamento de Quimica - UFMG Belo Horizonte - MG - BRAZIL ABSTRACT
The present work deals with the effect of the rare earth nature and the content of the oxide dopants on the stabilization process of zirconia based ceramics. There are two main interests in our work. The first is to verify the possibility of stabilizing a cubic structure of zirconia using a natural mixture of rare earth elements as dopant, and second, to study and to characterize its basic physical-chemical properties such as phase diagrams, zirconia stabilization models and dopant distribution. INTRODUCTION
Zirconia based solid electrolytes have been receiving great theoretical and technical interest as oxygen conductors materials. They are extensively used for thermodynamic and kinetic studies[1, 2], in electrochemical devices such as solid oxide fuel cells [3] and oxygen sensors [4].
For these applications, zirconia based solid solutions are used in a polycrystalline state, normally in fluorite phase that is characterized by a significant influence of the microstructure (grain boundary density, grain size homogeneity, impurity and dopant distribution, thermal history, etc.) on its transport properties. The nature and the dopant concentration that must be used for the stabilization of the cubic phase in zirconia have been studied by several authors [5, 6]. More frequently yttrium oxide is taken as dopant in concentrations ranging from 2 to 9 mole percentage. The partially and fully stabilized zirconias can be obtained when appropriated dopant amounts are employed. Some studies with ternary systems such as ZrO2-CaO-Y203 and ZrO2-Yb2O 3 -Y2 0 3 have been also reported in the literature. The present work deals with the effect of the rare earth nature and the content of the oxide dopants on the stabilization process of zirconia based ceramics. There are two main interests in our work. The first is to 303 Mat. Res. Soc. Symp. Proc. Vol. 346. 01994 Materials Research Society
verify the possibility of stabilizing a cubic structure of zirconia using a natural mixture of rare earth elements as dopant, and second, to study and to characterize its basic physical-chemistry properties such as phase diagrams, zirconia stabilization models and dopant distribution. We note that the use of these natural rare earth dopant mixtures may be of great economic interest since rare earth separation is a costly process. The studied system in this work is (ZrO2 )1-x (RE203)x. The dopant content x of rare earth cation (RE) in the solid solution varies from 0.07 to 0.11 and is close to 9 mole percent, that is the usual yttria content used to stabilized the fluorite phase in zirconia systems. The notations used hereafter to identify the samples are BXD or CXD where B or C stand for the zirconium butoxide or zirconyl chloride octahydrate respectively, D is the dopant (RE=rare earth oxides) and X denotes the dopant content, in mole percent. EXPERIMENTAL
PROCEDURE
Hydroxide co-precipitation technique was used for the preparatio
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