Stability of rare‐earth‐doped spherical yttria‐stabilized zirconia synthesized by ultrasonic spray pyrolysis

Abstract

Phase stability is one of the crucial requirements for any material that can be used at elevated temperature applications such as thermal barrier coating (TBC). The most traditional TBC material, partially stabilized zirconia, limits the operating temperature due to its phase transformation. Conversely, the low thermal conductivity of fully stabilized zirconia (YSZ) may enable effective reduction in the surface temperature on the coated component, while avoiding deleterious phase transitions, although still being subjected to sintering and grain growth. It has been reported that addition of rare‐earths as dopants to YSZ can significantly increase resistance to grain growth at high temperature. Keeping this under consideration, this work investigates the role of rare‐earths (lanthanum and gadolinium) in increasing thermal stability of YSZ microspheres, the building blocks for high‐temperature photonics for reflective TBC. The spheres were produced by ultrasonic spray pyrolysis, and the doping led to significant improvement of stability by significant inhibition of grain growth. While the individual dopants showed significant growth and sintering inhibition up to 900°C, co‐doping with 4% (in mol) of each (Gd and La) led to coarsening resistance up to 1000°C for 3 hours, when particles retained reasonable spherical features with nanometric crystallite sizes.

Thermodynamic and kinetic analyses of sintering in Al‐doped Y2O3 nanoparticles

“…Figure 2 and Figure show the DSC signals obtained from sintering Al‐doped Y 2 O 3 up to 1250℃ used for the measurement of both surface and grain boundary energies. Similar to the data obtained for interfacial energy measurements of undoped Y 2 O 3 and various other nanoceramic systems, exothermic heat effects starting above the calcination temperatures were observed 26,27,31,32 1) showed no changes in the crystal structure during the DSC experiments.…”

“…No references were found on modeling of the PIP process for CMCs, though experimental studies on this manufacturing process have been reported. Studies on polycarbosilanederived SiC ceramic 25 and SiC/SiC composite 26,27 have shown that porosity decreases and mechanical properties improve with the increasing number of PIP cycles. Zhu et al 28 show that increasing pyrolysis temperature and the concentration of SiC fillers in polycarbosilane polymer result in improved mechanical properties in two-dimensional Carbon/ SiC (C/SiC) composites fabricated using the PIP process.…”

Thermodynamics and kinetics of sintering of Y2O3

“…58 This is especially evident for the DSC curves of the samples with the smallest starting grain sizes, contrasting with previous data from similar experiments in the literature which show single DSC peaks of sintering. 32,59 Author Manuscript…”

Crack Propagation and Effect of Mixed Oxides on TGO Growth in Thick La–Gd–YSZ Thermal Barrier Coating

“…Moreover, Nafsin et al have studied the stability of Lanthanum-gadolinium-yttria stabilized zirconia (La-Gd-YSZ) complex coating [25]. They found further increases in thermal stability, with retaining the sphere shape and nanoscale crystallite size up to 1000 • C for at least 3 h, while at 1100 • C the spheres started necking but the spheres were still in shape [25].…”

“…Moreover, Nafsin et al have studied the stability of Lanthanum-gadolinium-yttria stabilized zirconia (La-Gd-YSZ) complex coating [25]. They found further increases in thermal stability, with retaining the sphere shape and nanoscale crystallite size up to 1000 • C for at least 3 h, while at 1100 • C the spheres started necking but the spheres were still in shape [25]. In this work, we used higher temperatures of 1200 and 1300 • C for the isothermal oxidation test on La-Gd-YSZ (Y-5 wt.%, Zr-65 wt.% and a little amount of other rare earth elements; La-0.15 wt.% and Gd-0.1 wt.%) coating.…”