ELECTROCHEMICAL DISSOLUTION OF TITANIUM IN SOLUTIONS OF SODIUM CHLORIDE AND HYDROFLUORIC ACID
We have studied the process of anodic dissolution of titanium (purity not less than 98.33%) in aqueous solutions of sodium chloride with the addition of hydrofluoric acid in galvanostatic conditions and by registration of potentiodynamic polarization curves. The paper shows the influence of potential sweep rate and the concentration of hydrofluoric acid on the characteristics of the titanium electrode polarization curves. It is found that an increase in the sweep rate of the potential promotes an increase in the magnitude of the peak currents on the potentiodynamic polarization curves of titanium anodic dissolution. In the range of variation in the potential sweep rate from 2 to 100 mV/s, the peak current of titanium anode oxidation increases by a factor of 15-20; while the magnitude of the current in the passive region increases by a factor of ~ 5. We established a joint influence of hydrofluoric acid concentration and the rate of potential sweep rate on the anodic behavior of titanium. At a potential sweep rate of 2-20 mV/s, there is a tendency to increase the peak current value with increasing concentration of hydrofluoric acid. At a sweep rate > 20 mV/s, an increase in the concentration of hydrofluoric acid leads to a decrease in the magnitude of the current maximum on the potentiodynamic polarization curve. The paper shows the effect of hydrofluoric acid concentration and the magnitude of the polarizing current on the intensity of electrochemical dissolution of titanium in galvanostatic conditions. It is found that in sodium chloride solutions, with an addition of HF ≤ 0.1 mol/l, titanium dissolves slightly, its oxidation rate does not exceed 0.5 mg/cm<sup>2</sup>·h. It is shown that the increase in the rate of titanium oxidation (by a factor of 5-10) in a solution of 1.0 M NaCl + 0.1 M HF in the absence of polarization and at low values of the applied current (about 5-10 mA) is due to its high chemical solubility in HF. It is found that an increase in the concentration of HF to 0.5-1.0 mol/l results in an increase of titanium anodic dissolution rate by a factor of 150-250 and 250-400, respectively. The paper also proves the possibility of controlling titanium anodic oxidation rate by varying the concentration of hydrofluoric acid, the rate of potential sweep rate and the magnitude of the applied anode current.