Organic Substrate Under The Action Of Calcium Carbonate Crystal Growth And Morphology Of The Control

In this dissertation, the nucleation and growth of CaCO₃ crystals under different organic additives were investigated. Calcium dodecyl sulfate (CDS), collodion membrane, L-glutamic acid and CDS/carboxylation chitosan complex were employed as organic additives, various series of calcium carbonate crystals with specific morphologies were produced. The detailed results are summarized in the following:1. Calcium dodecyl sulfate (CDS) was first used in urea aqueous solution to contronl the nucleation and growth of CaCO₃ crystals, in which calcium dodecyl sulfate (CDS) was employed both as an anionic surfactant and the source of calcium in precipitation processes of calcium carbonate (CaCO₃) crystals. The as-obtained vaterite with tabular sphere-shaped, bicone-shaped, dumbbell-shaped and apple-like morphologies, and the calcite with hexagonal platelet-shaped were produced. The possible formation mechanisms were discussed. It should be mensioned that, the synergistic effects of the concentration of CO₃^2- and pH value, as well as anionic dodecyl sulfate and positive NH₄⁺, were believed to play an important role on the morphologic selectivity and phase transformation from vaterite to calcite.2. A novel rod-shaped calcium carbonate (CaCO₃) crystal composed of calcite and aragonite was synthesized under the control of insoluble organic matrix collodion membrane and the collodion membrane can provide nucleation sites for calcium carbonate crystals. This rod-shaped structure is similar to the abalone shell in nature. In the present study, solid-solid phase transition from calcite to aragonite was observed. Additionally, the novel flower, lamellate, pancake-shaped vaterite were found to aggregate on the surface of the collodion membrane. The effects of experimental temperature and aging time on the structure and morphology evolutions of the as-synthesized samples were investigated in detail.3. The nucleation and growth of calcium carbonate (CaCO₃) crystals in the presence of L-glutamic acid were studied. L-glutamic acid can restraint the phase transformation from vaterite to calcite and stabilize the metastable vaterite. It was also found that the magnetic stirring was in favor of the formation of vaterite. 4. The nucleation and growth of calcium carbonate (CaCO₃) crystals in the presence of CDS/carboxylation chitosan complexes were investigated. Novel morphologies of vaterite, including hexahedron plate-shaped, top-shaped, and peanut-shaped were found. The present systems contained CDS-chitosan mixtures have not been used to investigate the crystallization and aggregation behavior of calcium carbonate crystals before. The CDS-chitosan mixture can repress the phase transformation from vaterite to calcite and stabilize the metastable vaterite.