Influence of Corrosion on the Effective Resistance of Amperometric Sensor

Abstract

It is shown that the corrosion of electrodes made of the valve metal (titanium) changes the structure of its effective resistance by increasing the contribution of Ohmic resistance of passive films on the metal– solution interface. It is shown that the passive films formed on titanium are monotonically aging, become more compact, and increase their Ohmic resistance under the condition of low aggressiveness of the electrolyte. This is indicated by the temperature coefficient, which is lower than 1%/°С. The processes of moderate and intense corrosion of titanium in acid and alkaline electrolytes are accompanied by periodic (with a period of more than a week) alternating processes of compactification and loosening of passive layers. Parallel with the general trend of increase in the effective resistance, we observed periodic changes both in its value and in the temperature coefficient. This leads to significant changes in the measurement errors of high-resolution sensors (with a period of oscillations of about one or two weeks). As temperature increases, the period of oscillations of measurement errors decreases. This promotes the intensification of damping of these oscillations (caused by the alternation of the limiting stages of current-forming processes) against the background of increase in the effective resistance of passive films on titanium.