A NEW TECHNIQUE FOR MEASURING THE FICKIAN DIFFUSION-COEFFICIENT IN BINARY-LIQUID SOLUTIONS

The present study details the development of a new technique for measu ring the Fickian diffusion coefficient in binary liquid solutions, and reports the coefficients obtained using this new technique for two el ectrolytic systems. The new method, called the decaying pulse techniqu e, takes advantage of the behavior of a semi-infinite system exposed t o 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 differ ent types of fluid pairs, and requires no knowledge of solution proper ties. The decaying pulse technique was used to measure the average dif fusion coefficient of potassium chloride in water and sodium chloride in water, at 18.5, 25.0, and 30.0 degrees C. The current experimental results were compared to those from other published investigations, an d were generally found to agree within the predicted uncertainty of th e current measurements +/-7.6%. (C) 1998 Elsevier Science Inc. All rig hts reserved.