Abstract
Coprecipitation synthesis of nanocrystalline india-stabilized zirconia with high surface area and codoping with MoO3, WO3, TaO2.5, or NbO2.5 is reported. The concentration of codopants was defined by the charge-compensating mechanism. Ethanol washing followed by azeotropic distillation and freeze drying were compared as dehydration techniques for the gels. As determined by XRD and Raman scattering, 9 mol% of InO1.5 plus charge-compensating dopants is sufficient to completely stabilize the high-temperature tetragonal phase of zirconia. The effect of alloying hexavalent and pentavalent oxides was secondary compared to the InO1.5 concentration in the retention of the tetragonal structure. Improved specific surface area of 106.1 m2 g‒1 and crystallite size between 8 and 9 nm were achieved through ethanol washing and subsequent azeotropic distillation even after calcination at 600 oC. This result is attributed to the effect of the incorporation of ethoxy and butoxy groups after the treatment of the gels in organic medium, as detected by FT-IR spectroscopy and DSC/TG.
Highlights
Thermal barrier coatings (TBC) have been widely used to protect metallic parts from high temperatures in gas turbines[1,2], providing substantial benefits to the engine[3]
With respect to the samples dehydrated by ethanol washing followed by azeotropic distillation (EW/AD), the complete stabilization of the t- phase was only achieved for samples with 9 mol% of InO1.5 plus additional charge‐compensating dopants: 9 mol% of NbO2.5/TaO2.5 or 4.5 mol% of MoO3/WO3
The effect of charge-compensating oxides in stabilizing the tetragonal zirconia phase seems to be secondary in relation to the amount of InO1.5, which probably occurs due to the low calcination temperature used, not allowing direct observation of the effect of codopants
Summary
Thermal barrier coatings (TBC) have been widely used to protect metallic parts from high temperatures in gas turbines[1,2], providing substantial benefits to the engine[3]. The application of TBC allows higher inlet temperatures of the gas turbine, thereby reducing the amount of cooling air and increasing the volume of the working gas These are key factors to improve the efficiency of land-based turbines for electrical power generation[4]. As the variety of fuels that can be used in gas turbines is quite extensive, there is a growing interest in non-traditional fuels such as petroleum coke or residual and heavy oils[4,11,12] In turbines burning these low-quality fuels, a high concentration of impurities, namely vanadium, phosphorus, and sulfur form salts responsible for the shortening of the YSZ-coating lifetime[11,13]. These molten salts are responsible for the depletion of stabilizing Y3+ ions from
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