UC Berkeley

The precipitation of barium sulphate in a rapid mixing device (Y-mixer) coupled with an instantaneous sample freezing device was studied in order to accurately measure the nucleation rate. In this Shock-Freeze Cryo-TEM (SFCT) approach, a small volume of solution was removed from the stream directly into liquid ethane by means of a gravitational guillotine. Using different pipe lengths to measure various residence times, it was possible to determine the particle size, morphology, numbers of primary particles and thus nucleation rate. The nucleation rates were found to be a strong function of Reynolds number, up to Re=3×104 (Re being inversely related to the micromixing time). The measured nucleation rates ranged between 2.79×1014 and 3.81×1017 # m-3 s-1 at supersaturations between 4×106 and 1×108. The measured particle sizes in this work (ranging from 62 to 320 nm for supersaturation values between 4×106 and 1×108) were smaller than those measured by previous researchers, possibly because previous work did not quench the reaction sufficiently fast and thus allowed the particles a longer time to increase in size. In summary, this work successfully achieved a fast, accurate and reproducible nucleation rate measurement that could also give information about particle morphology.