After the process, TBC spallation was observed on the front side of the specimens processed with 10, 5, and 2 vol.%TEOS, while the specimen of 0.5 vol.%TEOS was coated with a ~ 5 渭m thick SiO2 layer without any macroscopic damages. The surface of the coatings consisted of fractal-structured nodules at 10 vol.%TEOS, and of smooth grains at 0.5 vol.%TEOS. The spallation of SiO2-coated TBC was attributed to the thermal mismatch due to the difference in the thermal expansion coefficients of the two materials. Based on these results, the mixing ratio of TEOS to methanol was reduced to 0.3 vol.%, which produced a 1-2 渭m thick, smooth and homogenous SiO2 coating without any spallation of TBC. This deposition condition was chosen for the planned test to evaluate on the effects of the in situ deposition of SiO2 on the long-term durability of TBC-coated IN738LC specimens upon cyclic burner rig operations.