Reverse Micelle Synthesis of Zirconia Powders: The Use of Hydrogen Peroxide as Washing Solvent
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Reverse Micelle Synthesis of Zirconia Powders: The Use of Hydrogen Peroxide as Washing Solvent Harpreet Singh* and Olivia A. Graeve# Metallurgical and Materials Engineering University of Nevada, Reno 1664 N. Virginia Street – Mail Stop 388 Reno, NV 89557 ABSTRACT Yttria-stabilized zirconia nanopowders were synthesized using AOT/isooctane reverse micelles. XRD results showed that the powders were tetragonal with crystallite sizes ranging between approximately 1-50 nm depending on the thermal treatment given to the powders. BET surface area analysis of the powders gave a specific surface area of 230 m2/g for the assynthesized powders and 19.3 m2/g for the powders treated at 1000°C. This results in equivalent powder particle diameters of 4 nm and 52 nm, respectively. Washing of the powders is a very significant step for successful post-processing of powders obtained by AOT/isooctane reverse micelles. The use of ethanol and dry ether did not remove AOT, as determined from EDS measurements. Subsequent experiments showed that a novel solvent (hydrogen peroxide) was effective in removing AOT from the powders. The reason for the effectiveness of the new solvent is its capacity to decompose the AOT into weak acids, which are easily washed away with deionized water. INTRODUCTION ZrO2 is one of the best ceramic oxide materials for use as an electrolyte in solid oxide fuel cells [1, 2], as a catalyst support in the petrochemical industry, as a transformation toughened structural material, and as an oxygen sensor and oxygen pump. In particular, Y2O3-stabilized ZrO2 (YSZ) has a high oxygen-ion conductivity at elevated temperatures, which makes it suitable for use in oxygen sensors and oxygen pumps at elevated temperatures [3, 4]. Preparation of ZrO2 powders and the capacity to control ceramic powder characteristics is pivotal to the processing and performance of ceramics in many of these applications. The preparation of powders using the technique of reverse micelle synthesis achieves molecular level mixing during reaction, which allows careful control of the powder particle size. In the reverse micelle synthesis process, precipitation occurs simultaneously in billions of nanometric reverse micelles dispersed in an organic solvent, which allows uniform precipitation of powders. Compared with other methods used for the synthesis of ZrO2, the reverse micelle method has several advantages. The equipment needed is very simple, the synthesis is usually carried out at room temperature and ambient pressure, and the precursors are all commercially available. In addition, the technique can allow the formation of unagglomerated powders. The only hurdle to overcome is the contamination of the final products with the precursor organics, mainly AOT, which serves as the surfactant. Aerosol-OT or AOT is the commercial name for sodium sulfosuccinate. It is a common surfactant in many industrial applications. Combined with isooctane, to form an AOT/isooctane system, it is very commonly used for reverse micelle synthesis of inorganic nan
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