With a high-powered microscope, the particles of ordinary light calcium are more regular, and are usually spindle-shaped when fully dispersed, as shown in Figure 2. For light calcium carbonate, the particle shape of the synthetic product can be artificially controlled, and the control agent can be added during the carbonization process to achieve control.
At present, the developed control agents include inorganic acids, inorganic bases, organic acids (amino acids), alcohols, sugars, proteins and biopolymers with special structures. For example, carbonic acid with diamond shape, peanut shape, long rod shape, spherical shape and dumbbell shape can be made by using double hydrophilic block polymer PEG-b-PMAA at different concentrations and different pH values. For example, carbonic acid with spiral shape can be made by using dendritic polymer polyaspartic acid, as another example, spherical calcium carbonate can be obtained by adding anionic dextran.
Heavy calcium products due to the use of mechanical crushing and classification, the particle shape is generally cube, multi-prism, cuboid and other irregular forms, as shown in Figure 1. For different heavy calcium processing methods, the microscopic shape of calcium carbonate is different, for example, the calcium carbonate processed by rein grinding is spindle-shaped, and the calcium carbonate processed by air flow grinding is particle-shaped.
For heavy calcium carbonate from different producing areas, calcium carbonate has a fixed crystal form, and crushing and refining will not change the crystal form. Generally, heavy calcium of calcite is hexagonal crystal form, and heavy calcium of marble is cubic crystal form. For light calcium carbonate, in the specific carbonization preparation process, three crystal forms of calcium carbonate appear at different proportions at the same time, and to obtain a single pure crystal form, it is necessary to control the molding process.
The three crystal forms of light calcium carbonate are introduced as follows:
(1) calcite crystal form
The most stable crystal form of calcium carbonate belongs to the hexagonal crystal system. Under normal conditions, mineral calcium carbonate is stored in this crystal form. Calcium carbonate with such crystal form has large covering power, high whiteness, good purity, heat resistance, corrosion resistance and chemical resistance.
(2) arable crystal form
At room temperature, it is a metastable crystal form of calcium carbonate, which belongs to the orthorhombic crystal system, and the calcium carbonate with such crystal form has a high aspect ratio, and is commonly used in polymer reinforcement composite materials.
(3) Vaterite crystal type
The most unstable crystal form of calcium carbonate exists only in a small amount in organic materials, and will automatically convert to calcite crystal form or aragonite crystal in a short time. Calcium carbonate with such crystal form plays a very important role in biological life and health. It is found that dendrimer dielectrics and some low molecular weight polymer dielectrics can promote the formation of stable vaterite crystal form.