Study On Corrosion Resistance Of Al, Al₂O₃ And Al-Zn Coatings Deposited On Uranium

Uranium is chemically active, which is extremely corroded in many environments. Al, Al₂O₃ and Al-Zn coatings on uranium have been prepared by using magnetron sputtering deposition (MS or RMS), plasma spraying (PS) and thermal oxidation (TO) techniques to provide corrosion protection for uranium. Our experiments emphasized the correlation between micro structures and some properties of the coatings and tried to obtain the protective coatings with the comprehensively good properties, in which auger electron spectroscopy (AES), scanning electron microscope (SEM), and X-ray diffraction (XRD) were employed to investigate the composition, microstructure and crystal phase of the coatings respectively, and the properties test was primarily considered with the wear resistance and corrosion resistance of the coatings. The main experiment results are as the following.The coatings composition and microstructure are influenced significantly with the different techniques or process parameters. At -100V low bias voltage applied to uranium substrate, all of three coatings are closely dense, while the Al coatings are completely open dentritic at -300V. Bias voltages exert a small effect to the residual stress of Al coatings, but do a considerable effect to the coatings composition such as the preferential sputtering in Al-Zn coatings at -100V. With respect to Al₂O₃ coatings production, the TO and RMS techniques perform much better than the PS one. Interfacial atoms diffusion or covalence by a circulated-argon ion bombardment process could improve the adhesion strength between the coatings and the uranium substrate.The corrosion test, performed in 5wt% salt fog or with the electrochemical calculation of anodic polarization in 50μ,g/g potassium chloride aqueous solution, indicates the coatings densification corresponds with their corrosion protection to uranium. The denser the coatings are, the more effective their protection to uranium is. Compared with the Al coatings produced at -300V bias voltage and Al₂O₃ coatings produced with PS technique, the Al coatings at -100V and Al₂O₃ coatings with RMS and TO techniques are denser thus providing a better protection for uranium. The wear resistance test indicates, of three coatings, that of the Al₂O₃ coatings is the best one due to its nature characteristics. In addition, it is found that the Al-Zn coatings can change from anodic protection to catholic one with increase of the bias voltage.It is clear that the different techniques or process parameters employed have a strong effect to the coatings microstructures and do further effect to the coatings properties. As a result,of the comparison, the RMS or TO technique at appropriately low bias voltage can produce the Al₂O₃ coatings with good comprehension properties, by which the Al₂O₃/ Al gradient coatings as the long-term protection to uranium is a potential candidate.