Nucleation and growth kinetics in synthesizing nanometer calcite

The size of nanometer particles uniquely depends not only on the nucleus growth rate but also on the nucleation rate. This paper presents the effect of sodium tripolyphosphate on the microimages, synthesis reaction, nucleation and growth during the synthesizing of nanometer calcite using chemical analysis, SEM technique and Rosin-Ramuler probability statistics theory. The result showed that the calcium hydroxide carbonation reaction was inhibited by sodium tripolyphosphate adsorbed on the active growth sites. The SEM images revealed that the synthesizing of nanometer calcite was a multi-stable state process. When [Na5P3O10] = 0, 38.04 muM, the tiny calcite nuclei re-dissolved and the nucleation rate was negative at the final stage. The supersaturation and the nucleation rate increased in proportion to the concentration of sodium tripolyphosphate. The presence of sodium tripolyphosphate accelerated the nucleation of calcite and inhibited the crystal growth. During the crystallization of nanoscale calcite, the fluctuation nucleation, nucleus growth and coarsening growth may take place in series for a fine particle. To a whole carbonation solution, these three steps may occur simultaneously. At the final stage of the nucleation, the calcite crystal growth was controlled by a short-range diffusion and an interface reaction. The Zener-Ham model could not correctly describe the crystal growth. At the coarsening growth stage, the Zener-Ham model could not correctly describe the crystal growth yet. Once the steady nucleus had been shaped in the solution, the crystal growth was determined by a long-range diffusion, and the growth process accorded with Zener-Ham model quite well. (C) 2002 Elsevier Science B.V. All rights reserved.