Temperature-triggered Assembly of Ta ₂O ₅ hollow microspheres

Amorphous Ta ₂O ₅ nanoparticles were solvothermally synthesized at 150°C for 12 h in a mixed H ₂O ₂ and CTAB solution by using electrolyzed tantalum alkoxide as the starting material. The calcined samples were characterized by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that amorphous Ta ₂O ₅ with hemispheres structure are obtained from nanoparticles after calcination at 600°C for 5 h. Porous Ta ₂O ₅ microspheres are with an average diameter of 2 μm and a hollow cavity structure is self-assembled when subjecting to calcination at 900°C for 5 h, the thickness of the hole is about 150 nm and the diameter of the hollow part is estimated to be 1.5 μm. However, the size of tantalum pentoxide is decreased after calcination at 600°C and further decreased, at 900°C when anionic surfactant(oleic acid) is used instead of CTAB. The possible temperature-triggered microsphere assembly mechanism is discussed, and the abnormal phenomenon about the decreased tantalum pentoxide nano-particle is also reasonably interpreted.