Silica coating of synthesized Ta₃N₅ powders by the micro-emulsion method

We synthesized yellow TaON and red Ta₃N₅ by ammonolysis of amorphous Ta(OH)₅ between 800 and 1000 °C. Ta(OH)₅ was prepared by titration, using TaCl₅ as the starting material. Yellow TaON was synthesized at 900 °C for 2 h, and red Ta₃N₅ was synthesized at 1000 °C for 5 h. In general, red Ta₃N₅ powders were easily oxidized at 500 °C, with the color changing from red to white. To minimize the oxidation problem of Ta₃N₅ powders, we proposed a silica coating system using tetraethyl orthosilicate (TEOS) and 3-aminopropyltriethoxy-silane (APTES) as surfactants. The tonality of silica-coated Ta₃N₅ changes very little, indicating that the silica coating minimizes the oxidation of Ta₃N₅ nanoparticles.