Studies of the products from the reactions of co-acids containing concentrated HF and dilute HNO3 with Zircaloy-4

The pickling of Zircaloy with HF–HNO3 solution as an important surface treatment has been widely used in the nuclear materials industry. However, a thorough knowledge of the products from the reactions of HF–HNO3 system with Zircaloy still needs to be well established. In the present study, the acid solution containing HF (40 wt.%) and HNO3 (65 wt.%) with four volume ratios, 100:0, 94:6, 89:11 and 80:20, was employed and it reacted with Zircaloy-4 violently with gas releasing at an air pressure of 1 bar, a relative humidity of 30 ± 5% and a temperature of 25 °C. Meanwhile, white products formed within minutes. These products were identified by using X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The usage of the concentrated HF solution leads to the formation of crystalline ZrF4(H2O), while the usage of co-acids containing concentrated HF and dilute HNO3 results in the formation of crystalline ZrF4(H2O) and NH4ZrF5. In addition, with decreasing the volume fraction of HF and increasing that of HNO3 in the co-acid used, the weight fraction of crystalline ZrF4(H2O) decreases while that of crystalline NH4ZrF5 increases in the products obtained.