How is the polarization resistance Rp formed?
Ions serve as charge carriers, transporting charge to the electrode surface. When the electrode surface is too small or the ion concentration is too high, this charge-transfer process cannot proceed rapidly, leading to the formation of an ion cloud at the electrode surface that obscures the electrode. In the case of direct current, the initial current gradually decreases to zero. However, since conductivity measurements are performed using alternating current, only a finite additional resistance is introduced—though this resistance is, of course, undesirable.
This polarization effect can be reduced by the following methods:
1. Select an appropriate frequency for the corresponding conductivity measurement range.
2. Select an appropriate electrode constant (e.g., K = 1 or K = 0). The higher the conductivity value, the larger the electrode surface area or the greater the distance between electrodes required.
As a result, the current density at the electrode is maintained at a low level (typical value < 1 mA/cm²). 2 .
3. Select appropriate electrode materials and electrode surface treatments.
By adopting the aforementioned methods, the Kohlrausch electrode can be used in applications with a conductivity of 200 mS/cm.
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