Synthesis and Characterization of Nano-crystalline La 2 Zr 2 O 7 Film by Reactive Spray Deposition Technology for Applic
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Synthesis and Characterization of Nano-crystalline La2Zr2O7 Film by Reactive Spray Deposition Technology for Application in Thermal Barrier Coatings Yang Wang1, Rishi Kumar1, Justin Roller2 and Radenka Maric1 1 University of Connecticut, 97 North Eagleville Road, Storrs, CT 06269-3136 2 FEI Company, 5350 NE Dawson Creek Drive, Hillsboro, OR 97124
Abstract Lanthanum zirconate (La2Zr2O7) nano-crystalline films with cubic structure have been successfully prepared by a facile synthesis approach called reactive spray deposition technology (RSDT). La2Zr2O7 nanoparticles are produced by combusting a precursor solution of lanthanum acetylacetonate hydrate and zirconium acetylacetonate dissolved in an organic solvent mixture. The nanoparticles formed during the combustion process are directly deposited onto the substrate. The composition and microstructure of the as-deposited films are extensively characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The thermal diffusivities of the films are investigated by the means of laser flash method. 1. Introduction Some gas turbines and diesel engines require thermal barrier coatings (TBCs) to protect the metallic components exposed in extreme high temperature operating environment [1]. With the thermal insulation from TBCs, the higher gas inlet temperatures that are needed to improve the efficiency of these engines are allowable, and the requirements for the onboard cooling system can be lowered [2] and [3]. Yttria-stabilized zirconia (YSZ) as a top-layer of TBC has been widely adopted in the industry. However, when operated at temperature above 1200︒C, the YSZ coating is subjected to cracking failure due to volume expansion associated with crystal phase transformation. In recent years, rare earth zirconates have been rigorously investigated and are found to have high phase stability, low thermal conductivity and high melting point which are ideal thermophysical properties for TBC applications [4] and [5]. Among them, lanthanum zirconate (La2Zr2O7) with cubic pyrochlore structure is of special interest. La2Zr2O7 is structured with six octahedral of ZrO6 as the backbone and La3+ ions as the void filings. Since phase transformation does not easily occur with vacancies at the ion sites, this material remains phase stable up to its melting point of 2300 °C. Comparing to yttria-stabilized zirconia, La2Zr2O7 possess a lower thermal conductivity (1.56 W∙m-1 ∙K-1 vs. 2.1-2.2 W∙m-1∙K-1) and less tendency to sintering so the integrity of the porous structure in the coating can be preserved. Conventional synthesis methods, such as solid state reaction, co-precipitation, sol-gel and hydrothermal reaction, have been employed to produce La2Zr2O7 powders with high crystallinity [6-10]. Air plasma spraying and electron beam physical vapor deposition techniques are used to prepare high quality La2Zr2O7 films. However, these methods generally require either time-consuming processing steps or expensive equipment. Reactive spray deposi
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