Preparation of CaCO₃/Al(OH)₃ Composites via Heterogeneous Nucleation

As one of the most widely used inorganic fine powder fillers, calcium carbonate is cheap. However, considering its poor light transmittance, it is not suitable to be added to resin matrix composites that require high light transmittance. Aluminum hydroxide has good light transmission and flame retardancy, but it is more expensive than calcium carbonate. CaCO₃/Al(OH)₃ composites with a core-shell structure that showed a trend toward the performance of aluminum hydroxide not only improved the surface properties of CaCO₃, but also increased the added value of CaCO₃. In the present paper, CaCO₃/Al(OH)₃ composites were successfully prepared in sodium aluminate solution via heterogeneous nucleation. Four types of calcium sources, including calcite-type precipitated calcium carbonate, vaterite-type precipitated calcium carbonate, ground calcium carbonate with two different particle sizes as the precursors and supersaturated sodium aluminate solution as the substrate, have been deeply investigated in terms of their influence on the preparation of CaCO₃/Al(OH)₃ composites. Results showed that the calcium carbonate precursor greatly affected the formation of CaCO₃/Al(OH)₃ composites. Both the precipitated calcium carbonate and the small particle ground calcium carbonate are likely to undergo anti-causticization and a complexation reaction with it to generate 3CaO·Al₂O₃·6H₂O and 3CaO·Al₂O₃·CaCO₃·11H₂O, which go against the coating of calcium carbonate with aluminum hydroxide. Within the experimental range, the use of ground calcium carbonate with a particle size of 400-500 mesh is more suitable as a precursor for the preparation of core-shell CaCO₃/Al(OH)₃ composites.