Some electrochemical behavior of low corrosion metals III- Tantalum in aqueous solutions

The oxide film growth on Ta in 0.1 M solutions of HCl, HNO3, H2SO4, H2CrO4 and their respective sodium salts was examined at low current densities. The kinetics of film formation was stated and the local current density at open circuit was calculated in the tested media. The variation of the open circuit potential of Ta with time was traced in buffer solutions covering the range from pH 1 to 13. The results showed that the possibility of the metal to be used as an indicator electrode and was tested for acid-base and precipitation potentiometric titration. The equivalent point obtained was satisfactory and in accordance with other standard recommended electrodes

Polarographic study on the electrochemistry and hydrolysis of cations I-zirconium

Metal ions in aqueous solutions interact strongly with water molecules. The latter are bound to the ionic species via the oxygen atoms to form strong coordinate linkages by virtue of the lone electron pairs. The actual state of such species in solution is that of an aquo complex in which water molecules are regarded as ligands. Hydrolysis reactions are common to most cations and their degree differs from an ion to the other. Zirconium is a typical transition element with valence-electron configuration 4d[2]-5s[2], and its properties in aqueous solutions are determined by the electrostatic characteristic of the Zr4+ ion. The high charge, small radius and comparatively low ionization potential make it possible to classify Zr[4+]among the electrostatic complex forming ion. For the formation of a stable complex with ionic bonding, it is necessary not only that the central ion has a high charge and a small radius, but also that the ligand is able to satisfy conditions for ion-dipole interaction to a sufficient extent. Water has a considerable dipole moment and high electron affinity and is capable of forming stable aquo ions with Zr[4+] characterized by ionic bonding. Little work on the direct polarography of zirconium has been reported. Laubengayer and Eaton reported two reduction steps over a narrow pH range and limited zirconium concentration. They attributed the first wave to be due to hydrogen discharge, whilst the second one was ascribed to the reduction of quadrivalent zirconium to the metal. Potzak and Zaki reported a linear relationship between zirconium-dye reduction current and the zirconium concentration. Graham et al. reported an indirect method for zirconium estimation involving the precipitation of the metal with m-nitro benzoic acid. The polarography of zirconium salts in non-aqueous methanolic media of 0-1N LiCl was examined, and also of zirconium complexes with Solochrome Violet R.S. in various supporting electrolytes. In the present investigation a study of the hydrolysis of zirconium in aqueous media using the polarographic technique is undertaken