Abstract
The electrochemical behavior of tantalum in various concentrations of KOH solutions (0.1 M - 10 M), was investigated using the evolution of the open circuit potential in time, cyclic voltammetry and ellipsometric measurements. Depending on KOH concentrations, the open circuit potential measurements have shown three distinct behaviors concerning oxide film formation on the electrode surface and its dissolution. The cyclic voltammetry measurements were performed in various potential ranges, from -1.4 to 8 V, different concentrations of KOH solutions (0.1-10 M) and sweep rates ranging from 0.005 V/s to 1 V/s. In the passive region, very stable passive films were formed, which reduction has not been possible during cathodic polarization even at highly concentrated KOH solutions. In the trans-passive region, the very strong peak at 1.65 V was monitored, which nature and chemical composition is still not well known.
Highlights
Tantalum is known as a refractory metal because its melting point of 2996 °C is greater than that of platinum 1750 °C
The cyclic voltammetry measurements were performed in various potential ranges, from -1.4 to 8 V, different concentrations of KOH solutions (0.1 10 M) and sweep rates ranging from 0.005 V/s to 1 V/s
By investigating the evolution of open circuit potential (OCP) over time, in combination with in-situ ellipsometric measurements and cyclic voltammetry (CV) in larger concentration range of KOH solution and larger potential region in (CV) measurements, it is expected to obtain more information concerning formation and stability of passive films formed on Ta surfaces
Summary
Tantalum is known as a refractory metal because its melting point of 2996 °C is greater than that of platinum 1750 °C. Tantalum belongs to the group of valve metals because it develops a stable passivating layer spontaneously, when contacting air and/or water solutions. By investigating the evolution of open circuit potential (OCP) over time, in combination with in-situ ellipsometric measurements and cyclic voltammetry (CV) in larger concentration range of KOH solution and larger potential region in (CV) measurements, it is expected to obtain more information concerning formation and stability of passive films formed on Ta surfaces. For simultaneous electrochemical and in-situ ellipsometric measurements, the special cell of the Pyrex glass vessel was used. It was equipped with three cylindrical compartments for the working, counter and reference electrode, as well as an inlet and an outlet for bubbling inert gas. The electrolyte in the cell was exchanged in order to avoid any eventually formed soluble species
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