Instrumentation and Applications of a Tracing Potentiostat for Automatic Measurement of Polarization Resistance

Abstract

A tracing potentiostat was constructed, that records automatically the change in immersion potential and polarization resistance with time in the studies of corrosion or electroless plating. This potentiostat usually traces the immersion potential of test electrode. When a trigger signal operates, however, the sum of the immersion potential and the voltage of a triangular wave of amplitude ±8mV is fed to the potentiostat circuit as set-potential, so that a linear potential-sweep automatically starts from the immersion potential in any conditions. Polarization resistance is obtained from the slope of current-potential (time) curve at the immersion potential. The measurements by the tracing potentiostat were made on iron in acid and neutral solutions, nickel in molten nitrate salt, and cobalt in electroless cobalt plating bath. The polarization resistances obtained were compared with the rates of processes obtained by weight measurement. It was confirmed that the tracing potentiostat is successfully used to monitor the rates of corrosion and electroless plating.