Fabrication of Zirconia Coatings using Electrophoretic Deposition and Reactive Sintering
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Fabrication of Zirconia Coatings using Electrophoretic Deposition and Reactive Sintering Ying Yuan, Xin Wang and Ping Xiao∗ Manchester Materials Science Centre, University of Manchester, Grosvenor Street, Manchester M1 7HS, U.K. ABSTRACT Electrophoretic deposition (EPD) technique has been used to fabricate green YSZ/Al composite coatings with controlled thickness and morphology. Such green coating was transformed into the YSZ/Al2O3 composite coating during following thermal treatment in air at temperatures up to 1200o C. Suspension for EPD was prepared by attrition-milling a mixture of yttria-stabilised zirconia (YSZ) and aluminium (Al) in acetyl-acetone (ACAC). The attrition milling reduced the particle size of the powder mixture. A mechanical alloying behaviour is believed to control the agglomeration and the breaking of large Al particles. Attrition milling also reduced the YSZ crystallite size, which can be attributed to the chemical reaction between YSZ/Al particles and ACAC. Thermal analyses and dilatometry measurements of the green compact indicate the temperature range for oxidation of Al and its effect on sintering of the coating. The coating obtained from EPD in the suspension after a longer milling time was found to have more uniform in microstructure. INTRODUCTION Electrophoretic deposition (EPD) has been used to produce a wide range of materials due to its simplicity, versatility, and low cost of the EPD process [1,2]. A novel technique for fabricating ceramic coatings using electrophoretic deposition (EPD) and reaction-bonded aluminium oxide (RBAO) [3-5] has shown that the addition of aluminium to the green form composites not only leads to the formation of crack-free composite coatings, but also promotes sintering of ceramic coatings at relative low temperature [3]. RBAO process used in the above works was to overcome the problems caused by the shrinkage during sintering by the volume expansion associated with the Al→Al2 O3 reaction [6]. However, the ball milling method used in the previous works limited the homogeneity of the coatings produced. Few studies have addressed specifically the relationship between the particle size distribution, stability of the suspension, microstructure of green coatings and sintered coatings. A suspension for EPD is a complex system in which each component has a significant effect on deposition efficiency. Success in the EPD process and the microstructure of coatings are largely dependent on the suspension used. In this work, attrition milling, instead of ball milling, has been used to prepare suspension for EPD. Suspensions were characterised using X-ray diffraction (XRD) and particle size analyses as well as zeta-potential measurements. The microstructures of the sintered coatings were observed using SEM. Thermal analyses and dilatometry measurements have been used to study the oxidation of the Al and sintering in the coatings.
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Corresponding author. Fax: +44 161 200 3586. Email address: [email protected]
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EXPERIMENTAL PROCEDURES Suspensions we
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