Absorption of ammonia on tantalum hydroxide synthesized by a hydrofluoric acid method

摘要

Ammonia is strongly absorbed on tantalum hydroxide prepared by ammonia neutralization of TaF₇ 2− or TaF₆ − complexes. FTIR analysis of tantalum hydroxide shows a characteristic peak around 1,400 cm−1, attributed to NH₄ +. TG and FTIR analyses show that the NH₄ + decomposes at about 500 °C. The correct chemical formula of tantalum hydroxide prepared by ammonia neutralization of TaF₇ 2− or TaF₆ − is thus TaO _x (OH)_5-x (NH₄) _x . This conclusion is also confirmed by TG and FTIR analysis of tantalum hydroxide treated with various concentrations of inorganic acid at room temperature. The NH₄ + in tantalum hydroxide can be exchanged completely in aqueous HNO₃ solution, and the weight loss of the resulting sample is ended at about 415 °C by TG analysis. The NH₄ + can also be exchanged completely with aqueous H₂SO₄ solution; however, SO₄ 2− is weakly absorbed on the tantalum hydroxide. Finally, the NH₄ + can be exchanged partially with aqueous H₃PO₄ solution; however, PO₄ 3− is strongly absorbed on the tantalum hydroxide.