Corrosion and electrochemical behavior of certain alloys of uranium with zirconium, niobium, and molybdenum in aqueous solutions

Abstract

The corrosion resistance of uranium and its alloys in water has been studied in a number of works (for a survey of these studies, see [1, 2]). The electrochemical behavior of uranium was investigated in [3].Earlier [4] the favorable influence of such alloying additives as molybdenum, zirconium, and niobium on the corrosion resistance of uranium in water at 100~ was demonstrated. A number of alloys, which show the best results in the indicated work, were selected for further investigation. TheLr behavior was compared with the behavior of technical-purity uranium (basic impurity 1.5 atomic % carbon). The composition of the investigated alloys is cited in Table 2. The alloys were prepared by argon arc meltLng from technical purity uranium, iodide zirconium, and 99.5% pure niobium and molybdenum. Then they were homogenized at 1000~quenched from the T-region in oil, and tempered according to the system, at 650~ for 10 rain and at 500~ for 100 h. The alloy with 20 atomic %molybdenum was also investigated ha the quenched state.The alloys were tested at the temperatures 90 and 100~In view of a number of methodological dLfficulties, unavoidable in electrochemical measurements in distilled water, we used tenth normal solutions of sodium sulfate or sulfuric acid. As was shown by the control experiments, this had no significant influence on the nature of the curves obtained in comparison with tests in water, which was also noted in [1, 2]. Figure 1 presents the results of a potentiostatic investigation of the alloys, obtained at 90~ on the potentiostat of the Central Laboratory of Automation with exposure at each point from 1 to 3.5 h (depending on the intensity of the corrosion). All the data are cited with respect to a saturated calomel electrode. In the entire region of potentials, the investigated binary alloys U-Mo and U-Zr, as well as the ternary alloy U-Zr -Nb, possess increased corrosion resistance in comparison with uranium, while the ternary alloy U-Mo-Nb even corrodes more rapidly than uranium.Parallel corrosion tests were conducted at 100~ in media with various pH (Fig. 2) The numbers next to the curves correspond to the numbers of the alloys cited in Table 1; the curves were taken after preliminary cathodic polarization (I0 rain at a current density of 160-180 mA/cm2); v is the rate of corrosion.

Oxidation of a depleted uranium‐5 wt% molybdenum (U‐5Mo) alloy in UHV by AES and XPS

“…17 Alloying with molybdenum has also been shown by gravimetric methods and X-ray diffraction (XRD) to improve corrosion performance compared with unalloyed uranium, however, not to the same level as for niobium. [18][19][20] A recent XPS investigation into the effects of various surface preparation steps on the oxidation of a U-10 wt% Mo alloy found a protective role for molybdenum in the prevention of formation of higher uranium oxides, although this was following extended periods of exposure to 97% humidity. 21 To date, mechanistic studies that attempt to determine whether the initial process of U-Mo alloy corrosion exhibits similar characteristics to U-Nb alloys and whether any differences may have an effect on the lower protective performance of U-Mo are lacking.…”

“…Similarly, a U‐20‐at% Zr was shown by XPS to form ZrO 2 following 5 L O 2 dose, albeit to a lesser extent than uranium oxidation . Alloying with molybdenum has also been shown by gravimetric methods and X‐ray diffraction (XRD) to improve corrosion performance compared with unalloyed uranium, however, not to the same level as for niobium . A recent XPS investigation into the effects of various surface preparation steps on the oxidation of a U‐10 wt% Mo alloy found a protective role for molybdenum in the prevention of formation of higher uranium oxides, although this was following extended periods of exposure to 97% humidity …”