Tantalum Oxide Coatings as Candidate Environmental Barriers

Abstract

Tantalum (Ta) oxide, due to its high-temperature capabilities and thermal expansion coefficient similar to silicon nitride, is a promising candidate for environmental barriers for silicon (Si) nitride-based ceramics. This paper focuses on the development of plasma-sprayed Ta oxide as an environmental barrier coating for silicon nitride. Using a D-optimal design of experiments, plasma-spray processing variables were optimized to maximize coating density. The effect of processing variables on coating thickness was also determined. X-ray diffraction (XRD) was use to ascertain that the as-sprayed coatings were comprised of ␣-and ␤-Ta 2 O 5 , but were fully converted to ␤-Ta 2 O 5 after a 1200°C heat treatment. Grain growth of the Ta 2 O 5 followed a time dependence of t 0.2 at 1200°C.

Residual Stress and Microstructural Evolution in Tantalum Oxide Coatings on Silicon Nitride

“…Optimization of the parameters for plasma spraying tantalum oxide coatings with minimal porosity was reported elsewhere. 17 All of the coatings were applied to an as-fired surface that had been given a post-sinter oxidation treatment. All of the substrates (2.5 cm  2.5 cm  0.3 cm) were cleaned ultrasonically for 5 min in propanol prior to spraying.…”

Phase Transformations in the High‐Temperature Form of Pure and TiO2‐Stabilized Ta2O5

“…Ta 2 O 5 is an important material because of its useful dielectric, optical, catalytic, and chemical properties. [2][3][4][5][6] Most current optical and dielectric applications make use of the amorphous form that has a dielectric constant (K) of B27, but it has been shown that the TiO 2 -stabilized high-temperature form (H-Ta 2 O 5 ) exhibits significantly enhanced values of dielectric constant (as high as K 5 280 at room temperature). [7][8][9] The exact mechanism(s) for enhancement of K in TiO 2 -modified Ta 2 O 5 is under investigation, and requires a better understanding of the structure and phase transformations in pure and TiO 2 -stabilized H-Ta 2 O 5 .…”

D.C. Plasma Spraying

“…Moldovan et al [181] have sprayed Ta 2 O 5 coatings that can be considered for environmental barrier applications. The as-sprayed coatings were approximately 97-98 % dense and were composed of the low-temperature polymorph, β-Ta 2 O 5 and some α-Ta 2 O 5 .…”