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

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 A degrees 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 A degrees 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.