Titanium and zirconium are used extensively in the industry due to their exceptional corrosion resistance in most of the harsh environments, viz. strong acids and alkalies (1, 2). Ti is used in aerospace industry, biomedical implantations, and in several chemical industries due to its low density, high mechanical strength and corrosion resistance (1, 3-7). Zr is mainly used as a fuel cladding material in nuclear industries and in chemical industries due to its high resistance to corrosion and hydrogen embrittlement (8-10). Although these materials exhibit high corrosion resistance in harsh acidic and alkaline environment, they readily dissolve in acidic fluoride media.

Previous reports on the corrosion of Ti and Zr were mostly based on weight loss and volume of H2 evolution. Sutter et al (11) studied the differences in the corrosion of Ti and Zr in HF-HNO3 pickling solutions. They reported that the HF acts as a complexing reagent for both metals, and HNO3 acts as an oxidizing agent for Ti metal whereas it increases the film thickness for Zr metal. It is also reported that, compared to Ti metal, Zr will show superior resistance in acids such H2SO4 and HCl In this work, the effect of varying the concentration of HF on the corrosion current was investigated. The estimation of the corrosion current was done by comparing with Tafel analysis and the confidence in the corrosion current estimation was further enhanced by other electrochemical techniques such as, linear polarization techniques and electrochemical impedance spectroscopy at open circuit potential (OCP). The effect of HF concentration on the anodic polarization curves of Zr (12) and Ti (13-15) was studied and a four step mechanism with two adsorbed intermediates was proposed. Although Ti and Zr are in the same group of the periodic table, there was a qualitative difference in the anodic polarization behavior of these metals. Ti metals shows a significant drop in the current values in the passive region where as Zr metal shows a small decrease in the slope of the potentiodynamic polarization curve in the passive region. However it was proposed that anodic dissolution of Ti and Zr in acidic fluoride media occur via the same reaction pathway. It was found that-2