A new technique for measuring the Fickian diffusion coefficient in binary liquid solutions

The present study details the development of a new technique for measuring the Fickian diffusion coefficient in binary liquid solutions, and reports the coefficients obtained using this new technique for two electrolytic systems. The new method, called the decaying pulse technique, takes advantage of the behavior of a semi-infinite system exposed to a transient concentration pulse. The method permits simple, direct, and absolute determination of the diffusion coefficient, and requires measurement of only time and distance. It is applicable to many different types of fluid pairs, and requires no knowledge of solution properties. The decaying pulse technique was used to measure the average diffusion coefficient of potassium chloride in water and sodium chloride in water, at 18.5, 25.0, and 30.0°C. The current experimental results were compared to those from other published investigations, and were generally found to agree within the predicted uncertainty of the current measurements ±7.6%.