Comparison of the thermal decomposition of (NH4)3ZrF7 in air and N2 gas

• The comparison of the thermal decomposition progress of (NH 4 ) 3 ZrF 7 in air and N 2 gas at 340°C was investigated. • (NH 4 ) 3 ZrF 7 decomposes sequentially by the formation of (NH 4 ) 2 ZrF 6 , NH 4 ZrF 5 and finally NH 4 Zr 2 F 9 in air at 340°C. • For long time, the hydrolysis of NH 4 Zr 2 F 9 to form zirconium oxyfluoride-Zr(F, O) 2.706 occurs in air at 340°C • Pure ZrF 4 quickly forms at 340°C under N 2 gas in a short time. • High purity ZrF 4 can be obtained by heating (NH 4 ) 3 ZrF 7 at temperature ≥340°C under N 2 gas. To understand the effect of gas on the thermal decomposition process of (NH 4 ) 3 ZrF 7 , the comparison of the thermal decomposition progress of (NH 4 ) 3 ZrF 7 in air and N 2 gas at 340°C was investigated using scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) and X-ray diffraction (XRD). The results showed that (NH 4 ) 3 ZrF 7 decomposed sequentially in air at 340°C through a several-step: (NH 4 ) 3 ZrF 7 → (NH 4 ) 2 ZrF 6 → NH 4 ZrF 5 → NH 4 Zr 2 F 9 . After that, the hydrolysis of NH 4 Zr 2 F 9 to form zirconium oxyfluorides occurred slowly. However, pure ZrF 4 quickly formed at 340°C in a short time under N 2 gas. The result indicates that the using of N 2 gas not only accelerates the decomposition rate of (NH 4 ) 3 ZrF 7 and but also decreases the formation temperature of ZrF 4 .