Studies On Synthesis And Properties Of Functional Nano-CaCO₃

As one of the most important aspect of nano-science, nano-materials are getting the focus of material science. With the development of the nanotechnology, the research of nano-materials gets to be more in-deep in both fundamental research and industrial applications. It is a new challenge in nanotechnology that the synthesis of a polymer composites material which has the properties in both organic and inorganic components. During the past few decades, a great variety of composites have been recognized as innovative advanced materials, and promising applications have been applied to many fields, including optics, electronics, catalysis, mechanics, sensors, biology, and others. However, the application of nano-materials used in the Polymer composites depends on the dispersion, surface properties, and the structural morphology of nano-materials. Therefore, it is significant to prepare a series of functional nano-materials so that it can be added to the polymer material effectively.Calcium carbonate is an important industrial chemical. As one of the cheapest commercially available nano-materials, calcium carbonate is widely used in the fields such as rubber, paper, paint, and so on. At present, the synthesis of calcium carbonate can follow tow routes (1) carbonation method and (2) solution method. The first is a useful method in industry. Because the carbonation method is environmentally friendly and takes advantage of the availability of mineral resources. As a nano-material, the particle size, dispersion, structure and surface morphology determine the function and application of calcium carbonate. In this paper, a research on combine the techniques of chemical reaction and surface modification are implemented. In-situ surface modification technique is took place with different organic substrate during carbonation. As a result, a series of functional nano-CaCO3 are prepared under kinds of effective modifier. The results indicate that it is an available and ideal strategy. The main contents are summarized as follows:(1) Synthesis of nano-CaCO3 was carried out using carbonation method. Studied the effect of temperature on the particle size and analyzed the reason. The variation of pH, conductivity and polymorph of calcium carbonate with time for nano-CaCO3 synthesized makes us know better of the process of carbonation. A "second carbonation" way was developed, the calcium carbonate particles we got was smaller and less aggregation.(2) A carbonation route for the synthesis of hydrophobic chain-like nanometer calcium carbonate was studied. In the process, citric acid and cetyl acid were used as an organic substrate to induce the nucleation and modify the surface of calcium carbonate separately. The operating parameters such as temperature and the concentration of the organic substrate were varied to study their influences on the active ratio. The products were characterized by transmission electron microscope (TEM), X-ray powder diffraction (XRD), Fourier transform infra-red (FTIR) and Thermo gravimetric analysis (TGA).The results show that hydrophobic chain-like nanometer CaCO3 crystals were obtained in the presence of citric acid and cetyl acid. Whereas, only cubic CaCO3 crystals were obtained without citric acid and cetyl acid.(3) The carbonation route for the synthesis of hydrophobic calcium carbonate was studied. In the process, cetyl acid was used as an organic substrate to induce the nucleation and growth of calcium carbonate. The calcium carbonate particles were produced by means of carbonation of the mixture of calcium hydroxide and cetyl acid by bubbling CO2/N2 gas mixture. The operating parameters such as temperature and the concentration of the organic substrate were varied to study their influences on the active ratio of calcium carbonate particles. The morphology of the calcium carbonate particles was characterized with scanning electron microscopy (SEM). The synthesized calcium carbonate particles in the presence of the organic substrate are branch-like particles. The polymorphs were characterized with X-ray diffraction (XRD). (4) A carbonation route for the synthesis of calcium carbonate was studied. In the process, phosphate betaine and polyethylene glycol-based phosphate were used as an organic substrate to induce the nucleation and growth of calcium carbonate. In the presence of phosphate betaine and polyethylene glycol-based phosphate, the obtained hydrophilic calcium carbonate particles can stabilize in the glycol solution for a long time.(5) The different thermal decomposition characteristic of nano-CaCO3 and ordinary calcium carbonate was studied. Analysis reasons of the different thermal decomposition. It is due to the crystal defects of nano-CaCO3 The product of thermal decomposition is water. We can avoid it by heating and aging.