Suspension and Sol Plasma Spraying of a Complex Ba(Mg1/3Ta2/3)O3 Perovskite: Effect of Precursor Chemistry

Ba(Mg1/3Ta2/3)O3 (BMT), a high melting point refractory oxide, is envisioned as a thermal barrier coating material. In this study, three combinations of chemical reagents are investigated as BMT precursors: two suspensions (1. Ba acetate + Mg acetate + Ta oxide; 2. Ba nitrate + Mg nitrate + Ta oxide) and one sol (Ba nitrate + Mg nitrate + Ta ethoxide). A hybrid suspension / sol plasma spray process is designed to axially inject these precursors into an RF thermal plasma torch to synthesize BMT and to deposit nanostructured coatings. Thermogravimetric analysis and differential thermal analysis (TG/DTA) are applied to investigate the BMT formation process. Parameters such as precursor proportion, precursor feed-rate and plasma power are studied in regards to the coating phase structure. The results indicate that the combination of 4 ml/min feed rate and twice the Mg stoichiometric amount shows the best results when using Ta oxide. When choosing nitrates as Ba and Mg precursors, crystalized BMT can be obtained at lower plasma power when compared to acetates. Finally, a comparison between suspension (with Ta oxide) and sol (with Ta ethoxide) spray processes shows that a finer microstructure is obtained with sol precursors, as expected.