Corrosion of Zirconium in Halogenide Melts
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CORROSION OF ZIRCONIUM IN HALOGENIDE MELTS А. О. Omel’chuk1, 2 and О. О. Andriiko3 We propose a method for the evaluation of stability of the corrosion products of zirconium in melts of different compositions. The method is based on the analysis of the dependence of the equilibrium potential of zirconium electrode on the initial concentration of its compounds in the oxidation state 4+. It is discovered that zirconium compounds in the oxidation state 2+ are in equilibrium with the metal in all investigated systems and their stability depends on the composition of the melt and decreases in the following order: (NaBr–KBr) > KBr ≥ KCl > (LiCl–KCl). It is also established that, parallel with zirconium compounds in the oxidation state 2+, the investigated systems contain its compounds in the other oxidation states. The stability of these compounds in bromide melts decreases in the following order: Zr(II) (NaBr–KBr) > Zr(IV) (NaBr–KBr) > Zr(II) (KBr) > Zr(IV) (KBr). In chloride melts, the observed sequence has a somewhat different form: Zr(II) (KCl) > Zr(IV) (KCl) > Zr(II) (LiCl–KCl). Lithium is present among the corrosion products in LiCl–KCl melts. We also determined the thermodynamic characteristics ( ΔH and ΔS ) of equilibria of the corrosion products of zirconium with the investigated melts. Keywords: zirconium, halogenide melts, corrosion products.
Zirconium is one of the metals without which it is impossible to imagine subsequent development of the contemporary science and technology and, in particular, of the nuclear power engineering. Zirconium is used as a base material of the shells of fuel elements of nuclear reactors. Moreover, it is proposed to use molten salt mixtures based on zirconium tetrafluoride as carriers of nuclear fuel and heat carriers in the reactors of new generation [1]. The high corrosion resistance of zirconium makes it an irreplaceable component in manufacturing biocompatible alloys resistant to the action of biological media used in medicine for the production of different implants, endoprostheses, medical instruments, etc. The alloy of zirconium with niobium exhibits superconducting properties. Zirconium alloys in the form of structural materials are used in the production of acid-resistant chemical reactors, pumps, and tableware. Actually, Ukraine occupies the third place after Australia and Republic of South Africa by the resources of zirconium in the form of ZrSiO 4 zirconium ores. However, unfortunately, our country does not have its own zirconium production. At present, the only known method for the production of zirconium is based either on the reduction of its halogenide compounds by metals (calcium, magnesium, and sodium) or by the electric currents from molten electrolytes [2]. The ability of zirconium to interact with halogenide melts decreases its yield by current, promotes its contamination with foreign metals, and leads to the instability of the mode of electrolysis and the fracture of structural materials. Hence, the data on the interaction of zirconium with halogenide melts i
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