PURPOSE: To make it possible to obtain high-purity niobium (tantalum) pentoxide useful as optical raw materials and raw materials for electronic materials by previously dipping a calcining crucible in a hydrofluoric acid solution and then treating the crucible with a hydrofluoric acid solution containing niobic (tantalic) acid dissolved therein.
CONSTITUTION: An oxide crucible is dipped in a hydrofluoric acid solution (preferably in a concentration within the range of 0.5-55wt.%) for 1-20hr (at 20-50°C temperature) and dried at 20-100°C for 2-10hr. The resultant crucible is then subjected to dipping treatment in a solution prepared by dissolving niobic or tantalic acid in 0.2-37wt.% concentration (expressed by in terms of oxide) in hydrofluoric acid for 2-48hr. The crucible is subsequently dried at about 150°C for 10-24hr and then calcined at 800-1000°C for 1-5hr. The crucible treated as described above is used to calcine niobic or tantalic acid to afford niobium or tantalum pentoxide.
TANAKA TADASHI
MUNENO YASUSHI
