Nucleation Phenomena Occurring in Aqueous Solutions Supersaturated with Calcium Sulfate

Abstract

<p>An extensive study of the nucleation phenomena of CaSO4.2H2O under various experimental conditions was undertaken. The droplet technique, a method of isolating mote-free portions of solution, was used along with a photomicrographic method of recording the results of nucleation within the droplet population.</p> <p>Experiments performed at constant temperature, super-saturation and calcium-sulfate ratio, yielded unconfounded empirical relationships between various independent and dependent nucleation variables. The most significant of these was the relationship between the lag time and the nucleation rate. Recognition of a relationship between these variables led to an extension of the droplet technique to much lower supersaturations. Also, evidence was found for two distinct pre-nucleation processes, a lag and an induction time.</p> <p>The functionality between the nucleation rate and the calcium-sulfate ratio was studied. It was concluded that the classical definition of supersaturation must include the calcium-sulfate ratio.</p> <p>Classical thermodynamic parameters were calculated at four experimental temperatures. Most significant of these produced a solution phase diagram for CaSO4.2H2O.</p> <p>With the information obtained above, designs of droplet experiments with variable driving force were evaluated, taking into account the changing supersaturation and the calcium-sulfate ratio with time. Mathematical models were also developed to handle the data collected from these experiments.</p> <p>The mechanism of nucleation in aqueous solution was discussed in terms of a new non-classical model using, as a source of information, all the experimental results.</p>