Development of an Experimental Method to Measure Nucleation Rates in Reactive Precipitation

Measurement of the stationary nucleation rate as a function of supersaturation in reactive precipitation requires that nucleation and growth of the crystals to an observable size take place under well-controlled hydrodynamic conditions and at a constant supersaturation. An experimental method was chosen that is based on the measurement of the increase of the particle concentration with the increase of the residence time in a precipitation tube. This method was applied to measure the nucleation rate for the pH shift precipitation of the molecular compound H 4 EDTA. The parameters A and B in the classical nucleation theory equation were derived from the measured nucleation rates. A value of A = (5.7 ± 1.0) × 10 15 m -3 s -1 was found for the intercept with the ordinate and a value of B = (3.3 ± 2.0) × 10 2 was found for the slope. The estimated value for parameter A is lower than the theoretical value of A HON = 10 33 m -3 s -1 for homogeneous nucleation. Using the experimentally determined value for B the interfacial energy is found to be γ = 21 ± 9 mJ m -2 compared to a theoretical value of γ HON = 38 mJ m -2 based on bulk properties. The experimentally obtained values for A and γ indicate heterogeneous nucleation.