Investigation on Parameters Influencing the Electrodeposition of Niobium-Based Layers

Abstract

The refractory metal niobium is used in technical applications because of its excellent corrosion and wear properties and as alloying element in steel or in superalloys for high temperature applications. In order to open new fields of application with maximum material efficiency, electrochemically produced niobium protective layers are suitable because they can increase the life-time of critical components. In principle, the electrochemical production of niobium-based layers is possible. However, due the very cathodic standard potential of refractory metals they cannot be electrodeposited from aqueous electrolytes. The ionic liquids (ILs) allows electrochemical deposition of niobium due to its high electrochemical stability (5 – 6 V electrochemical window) and low melting point <100°C. Usually metal halides (e.g. NbCl5) are used as precursors for electrochemical niobium deposition. The transfer of five electrons in several individual steps results in a complex reduction mechanism that can adversely affect the film formation, e.g. by formation of stable intermediates. Applying higher temperatures, additives (e.g. [BMP]Cl, LiCl) or pulsed potentials, the electrode/electrolyte interface changes and the deposition of niobium can be specifically influenced. Another possibility for optimizing the niobium-based layers is based on pre- and post-treatment (e.g. anodic etching). This contribution will discuss the influence of temperature, additives as well as the use of special pulse parameters on electrochemical niobium deposition. The aim is to find suitable deposition, pre- and post-treatment conditions and thus to optimize the resulting niobium-based layers. By means of various techniques such as cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical quartz microbalance (EQCM), as well as scanning electron microscopy, a better understanding of the reduction mechanism of niobium halides in ILs in the presence of selected additives shall be obtained.