SU401916A1 - METHOD FOR DETERMINING PH IN THE CATHODE REACTION ZONE - Google Patents

Description

one

The invention relates to corrosion-electrochemical research methods and can be used in research laboratories and electroplating shops.

The proposed method for determining the pH in the cathodic reaction zone is based on the study of the potential of the onset of the metal oxidation reaction with the formation of oxides, hydroxides or other compounds, strictly dependent on the pH of the solution. The known methods for determining the pH of the near-electrode layer have several disadvantages.

The proposed method makes it possible to more accurately and easily determine the pH of the cathodic reaction zone due to the fact that, after cathodic polarization, the anodic polarization curves are removed in buffer solutions with different pH, the calibration curves for the beginning potential of formation of oxide films on the pH of the buffer solution are obtained. whereupon the electrodes are anodically polarized in the test solution with the construction of polarization crises and pH values are found on the calibration curves according to the value of the potential of formation of oxide films.

Platinum, nickel and other electrodes can be used as electrodes for determining the pM cathodic reaction zone.

FIG. 1 shows the polarization characteristic of the metal; in fig. 2 - calibration curves.

According to the proposed method, the anodic polarization curves 1 of the electrodes are removed (after preliminary cathodic activation (i 3 ± 0.005 mA / cm) in buffered solutions with different pH values (from 2 to 14). From the obtained polarization curves (Fig. 1) determine the value of E for each pH and build calibration curves 2-4 (Fig. 2). The dependence of E - pH for electrodes from Zn, Pt, Ni is described by the equations:

EI (Zn) -0.48 + 0.060 pH, E | (Pt) -0.05 + 0.060 pH,, (Ni) 0.13 + 0.060 pH.

Next, the anodic polarization curves of the electrodes are removed by the potentiodynamic method or the method of removing charge curves with automatic recording, respectively (E) or (t) in unbuffered working solutions after preliminary cathodic polarization at different current densities rk, and determine the dependence of EI on rl ;.

Using c :) cathodic curves 2-4 (Fig. 2) and Et-g: ;, it is easy to determine the pH of the cathodic reaction zone, depending on

cathode current density in a short period (3-5 minutes).

The accuracy of determining the pH of the cathodic reaction zone depends on the rate of removal of the polarization curves (the higher the latter, the closer the measured pH value to the true one). Therefore, when taking charge curves with an oscillographic recording of ns tei ni from t with instantaneous switched cathode current to anodic, the average pH hardly differs from its true value for a given cathode current density.

Subject invention

The method for determining the pH in the cathodic reaction zone on the surface of metals, but which metal electrodes are lowered into the electrolyte, is cathodically polarized at predetermined current densities, characterized in that, in order to improve the accuracy and expand the field of application, preliminary cathodic polarization is removed anodic polarization and optic curves in buffer solutions with different pH set points, determine the potential for the onset of formation of oxide films depending on the pH of the buffer solution, the anode electrode being polarized comfort in the test solution with the construction nol polarization curves and meaningfully oxide films form a potential on the calibration curve are T pH.

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