The Determination of the Corrosion Rate of Zinc in Solution by the Differential Pulse Method

Abstract

The electrochemical measurement of the corrosion rate of zinc in nearneutral solutions using a differential pulse polarograph has been achieved to a greatly improved accuracy compared with previous w~rk. The perturbation of the corroding system is minimized as the potentiostatic polarizing pulse is applied for only 60 msec. The double layer charging of the electrode is monitored on an oscilloscope and the faradaic current measurements made by the normal Y recorder output of the polarograph. The iR correction facility on the polarograph is used to determine the Tafel parameters and can also be used if resistance overvoltage is a problem during the polarization resistance measurements. Four different solutions are examined where the cathodic processes are either separately or jointly oxygen reduction or hydrogen evolution. Where only one cathodic process occurs, the correlation of the weight loss with the corrosion current calculated by the Stern-Geary method is within 7%. Where two cathodic processes occur, errors of up to 15% are encountered.Recent studies on the corrosion of zinc in aerated near-neutral aqueous solutions (1-3) highlight two important areas which have been overlooked in past investigations. The first is a comprehensive study of the cathodic reactions which control the rate of corrosion of zinc in these solutions. Despite the common use of zinc as a sacrificial coating, a thorough study of the oxygen reduction reaction on zinc has been reported only recently (1) and it is obvious from this work that a concurrent hydrogen evolution reaction occurs in near-neutral solutions. Therefore, the exact nature of the cathodic reactions on zinc still requires further investigation to determine the extent of the hydrogen evolution in near-neutral solutions.The second area where further research is required is in the electrochemical methods for determining instantaneous corrosion rates. When studying corrosion reactions and particularly at rotating ring-disk electrodes, it is important to be able to monitor the corrosion rate of the disk because the cathodic reactions are usually surface dependent and, therefore, vary throughout the course of any one experiment. The refinement of simple methods such as linear polarization (4, 5) by Oldham and Mansfeld (6, 7) and the derivation of new methods by Barnartt (8) and others (9-11) have not produced any dramatic improvements in the correlations between electrochemically calculated corrosion currents and the weight loss for zinc freely corroding in aqueous solution. Impedance measurements (12) have been shown to yield reasonably accurate corrosion rates for steel, but they are limited to reactions where the corrosion current does not alter during the course of the experiments. In practice, this does not usually occur, particularly where corrosion products are formed on the surface.It has been our experience with corrosion rate measurements that the inaccuracies in determining the polarization resistance, AE/Ai, and Tafel parameters usually result in far greater errors...

Effect of hydrogen carbonate and chloride on zinc corrosion investigated by a scanning flow cell system

“…Hence the curvature is dominated by the anodic (cathodic) reaction. This would be consistent with a diffusion limited cathodic reaction in solutions A-D. Diffusion limited oxygen reduction on corroding zinc was reported by many studies [3,37,[45][46][47]. On the other hand, in solution E, the larger polarization resistance for anodic pulses indicates, that the curvature of the polarization curvature is dominated by the cathodic process.…”

“…The observed drift of the corrosion potential is compensated by linear interpolation (Fig. 2, inset) avoiding problems with potential drift described in References [37,38]. The amplitude of the potential response DE is a measure of the polarization resistance R p = DE/Di and hence the reactivity of the interface.…”

“…However, impedance spectroscopy is typically too slow to follow a rapidly changing system and potentiostatic pulses require a precisely known and constant corrosion potential [37,38]. Therefore small/short galvanostatic pulses (Di = 6.7 mA cm À2 for 15 s) in both anodic and cathodic direction are successively applied at regular intervals of the OCP experiment and the potential response is recorded.…”

Corrosion susceptibility of Zn–Al alloys with different grains and dendritic microstructures in Nacl solutions

“…Electrochemical techniques have been used in a number of studies on the corrosion of zinc in different solutions . The kinetics of the zinc electrochemical reaction processes such as dissolution, deposition, hydrogen evolution, oxygen reduction, passivation, and surface film formation, has been the subject of numerous electrochemical studies using different techniques such as dynamic polarization [4,[7][8][9][10][11][12][13][14][15][16][17][18][19][20][21], steady-state polarization [6,10,19,[22][23][24][25][26][27][28][29][30][31], measurement of current density-time transients [23,[32][33][34][35], measurement of potential-time transients [23,30,31,[33][34][35][36][37][38][39][40], rotating electrode [4,…”

Energetic Zinc Ion Chemistry: The Rechargeable Zinc Ion Battery

“…In a mild ZnSO 4 or Zn(NO 3 ) 2 aqueous solution containing Zn 2+ ions, the electrochemical dissolution and deposition process of zinc can occur above and below 0 V vs. Zn 2+ /Zn as shown in Figure 2 (red line). [7][8][9][10][11][12] Because of its relatively low potential, this rapid and reversible process is ideal as the anodic reaction…”