Synthesis and Phase Stability of Scandia, Gadolinia, and Ytterbia Co-doped Zirconia for Thermal Barrier Coating Application

Abstract

Scandia, gadolinia, and ytterbia co-doped zirconia (SGYZ) ceramic powder was synthesized by chemical co-precipitation and calcination processes for application in thermal barrier coatings to promote the durability of gas turbines. The ceramic powder was agglomerated and sintered at 1150°C for 2 h, and the powder exhibited good flowability and apparent density to be suitable for plasma spraying process. The microstructure, morphology and phase stability of the powder and plasma-sprayed SGYZ coatings were analyzed by means of scanning electron microscope and x-ray diffraction. Thermal conductivity of plasma-sprayed SGYZ coatings was measured. The results indicated that the SGYZ ceramic powder and the coating exhibit excellent stability to retain single non-transformable tetragonal zirconia even after high temperature (1400°C) exposure for 500 h and do not undergo a tetragonal-to-monoclinic phase transition upon cooling. Furthermore, the plasma-sprayed SGYZ coating also exhibits lower thermal conductivity than yttria stabilized zirconia coating currently used in gas turbine engine industry. SGYZ can be explored as a candidate material of ultra-high temperature thermal barrier coating for advanced gas turbine engines.

Synthesis and phase stability of zirconia-lanthania-ytterbia-yttria nanoparticles; a promising advanced TBC material

“…The precipitated product was rinsed in distilled water and thereafter was dried at 70°C for 24 h to obtain the precursor powder. This was followed by the calcination process performed at 1000°C for 2 h, which has also been reported by other researchers for the synthesis of similar defect cluster TBCs [5,17].…”

“…Tetragonality parameter ( c a ffiffi 2 p ) is an important factor for ZrO 2 tetragonal phase investigation [5,17]. In compounds such as M 2 O 3 -ZrO 2 , where M is Yttrium or a rare earth element, the tetragonality depends on the cooling rate of calcination process and also dopant concentration but independent of dopant type [22][23][24].…”

“…In recent years, zirconia combined with a primary stabilizer (about 6 Mol.%) and at least two additional cationic oxide dopants (about 4 Mol.% of two oxides), known as "defect cluster TBCs" [1,5,17,18] have attracted considerable attention due to their higher phase stability and higher service temperatures compared to YSZ [5,17].…”

“…Qi-Lian Li et al [17] reported that 5.5 Mol.%Sc 2 O 3 -2 Mol.%Gd 2 O 3 -2 Mol.%Yb 2 O 3 -ZrO 2 exhibits excellent stability to retain t-prime zirconia phase even after exposure to high temperature (1400ºC) for 500 h, which was associated with no tetragonal to monoclinic phase transition upon cooling.…”

“…-ZrO 2 compound synthesized by co-precipitation method, for which the phase stability was investigated after a heat treatment at 1300ºC for 50 h. Their study showed that the given compound exhibited an excellent phase stability due to full retention of t-prime zirconia phase and restriction of tetragonal to monoclinic phase transition upon cooling. Bahamirian et al [5] and Qi-Lian Li et al [17] suggested the co-precipitation method as a technologically simple, cost-effective, and capable of producing homogenously dispersed nanopowders with complex composition.…”