Effect of HF Concentration on Anodic Dissolution of Titanium

Abstract

Anodic dissolution of Ti metal in varying concentrations of hydrofluoric acid (10-1000 mM HF) was investigated using potentiodynamic polarization and electrochemical impedance spectroscopy. Polarization curves obtained at all concentrations of HF solution showed that current initially rises with potential, and decreases at higher potentials. Complex plane plot of the impedance spectra of Ti dissolution in 25 and 50 mM HF solutions exhibited three capacitive loops in the active region and a capacitive behavior with negative resistance in the passive region. The surface was characterized using X-ray photoelectron spectroscopy. A four step mechanism with chemical and electrochemical dissolution steps was employed to model Ti dissolution. The analysis shows that the simulated results match the polarization trends satisfactorily in all the solutions investigated. The model predicts that HF − 2 and remaining HF are the species that influence chemical and electrochemical dissolution steps respectively. The estimates of surface coverage values of the adsorbed species showed that with increasing over potential, the metal surface was progressively covered with oxide film, while an increase in nominal HF concentration leads to a decrease in fractional surface coverage. Titanium is used as engineering material in medical implants, aerospace applications, and in industrial applications by virtue of its low density, high strength and high corrosion resistance.1 Due to the presence of a tenacious passive oxide layer on its surface, Ti is highly corrosion resistant in most of the harsh chemical environments. 2,3However, the oxide layer readily dissolves in acidic fluoride medium. The anodic dissolution phenomena of Ti in fluoride media is important not only in corrosion but also in several technologies and industrial applications such as pickling of Ti, 4 manufacture of Ti based automobile parts, 5 and formation of self-organized TiO 2 nano tubes. 2,3,6Ti dissolution in fluoride medium has been studied extensively, and its dissolution in acidic fluoride media depends mainly on the concentrations of various species formed by HF dissolution, pH of the solution and temperature.3,6-8 Straumanis and Chen measured the volume of hydrogen produced during Ti dissolution in HF and proposed that the reaction order is 0.66 when the HF concentration is below 0.2 N and unity when it is more than 0.2 N.9 Ti dissolution in a solution of 0.1 N HF + 1 M HCl was measured at various temperatures, and the order was reported to be 0.76 while the activation energy was 6.9 kcal/mol. 10 HF, in combination with HNO 3 and a few other additives such as acetic acid, H 3 PO 4 , dodecyl benzene sulfonic acid, carbamide, sodium benzoate or sodium nitrate, have been used for chemical milling of In Ti pickling, addition of nitric acid is used to prevent hydride formation at the metal surface, which can lead to hydrogen embrittlement. 16 Ti dissolution in HF + HNO 3 solution is modeled using a mechanistic approach with Ti 3+ and TiO 2 as intermediate species. 1...

Investigating products of titanium dissolution in the presence of fluoride ions with dual dynamic voltammetry

“…The qualitative interpretation of the measurements, outlined above, remains the same for fluoride concentrations between 5 and 20 mM, although the intensity of the ring current signals (the amount of dissolved species) grows in strict correlation with the fluoride concentration. This is shown by Figure 4 and can also be expected based on literature [5,14].…”

“…Due to its extensive application, the electrochemical stability of titanium has been the subject of investigations for more than fifty years [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. The pure metal itself, and also some of its alloys are widely applied as materials of dental implants and braces.…”

Mechanistic Analysis of Anodic Dissolution of Zr in Acidic Fluoride Media

“…The current values are high and a significant dissolution continues to occur. For other valve metals such as Ti, 18,19,26 Nb, 27 and Ta, 28 a rapid decrease in current density is reported at potentials beyond the transition potential. Zr metal shows unusual behavior in the passive region compared to the other valve metals.…”

Study of on the Electrochemical Behavior of Titanium in Acidic Bromide Solution by Recording the Potentiodynamic Polarization Curves

“…M.S. Amrutha used a four-stage mechanism to determine chemical constants by investigating of Ti in varying concentrations of hydrofluoric acid (0.01 M÷1.0 M) through applying potentiodynamic polarization and electrochemical impedance spectroscopy methods [2]. F. Fasmin presented a kinetic model of titanium electrode anode dissolution in 0.1 M hydrofluoric acid in active and passive regions [3].…”