FORMATION AND STRUCTURE OF CARBONATE PARTICLES IN REVERSE MICROEMULSIONS

The carbonation of calcium hydroxide in solution in the presence of sulfonate surfactant has been studied by SAXS, QELS, and TEM techniques. We show that the starting solution is a water-in-oil (w/o) microemulsion containing preexisting micelles of about 10Åin diameter. The reaction leads to well-defined amorphous calcium carbonate particles of a typical size of 20 to 50Å. We also demonstrate that: (1) only 10% of these micelles are nucleated and give stable colloidal amorphous calcium carbonate particles, (ii) the reaction takes place in the polar micellar core, and (iii) the reaction is dependent upon the water content of the solution. The growth of the calcium carbonate particles is made possible by a dynamic exchange with the unnucleated micelles, which provide both the necessary lime and the additional surfactant molecules required to stabilize the colloidal particles. © 1991 Academic Press, Inc. All rights reserved.