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Yuan Lei's Little Knowledge | Application of Calcined Kaolin in Architectural Coatings

Release time:

2024-01-29 09:34

Kaolin minerals are composed of kaolinite, kaolinite, perlite, halloysite and other kaolinite cluster minerals, the main mineral composition is kaolinite. The crystal chemical formula of kaolinite is 2SiO2 ● Al2O3 ● 2H2O, and its theoretical chemical composition is 46.54% SiO2,39.5% Al2O3, and 13.96% H2O. Kaolin minerals belong to 1:1 type layered silicate.

 

 

Application of Calcined Kaolin in Building Materials

1, the new gelding material-soil polymer cement.

Soil aggregate cement is a new type of cementitious material different from ordinary Portland cement. Polymeric cement is based on kaolin as raw material by low temperature (500-900 ℃) calcination, the following reaction:

2n[Si]2O5,Al2(OH)4]→ 2(Si2O5,Al2O2)n+ 4nH2O

This reaction transforms the kaolinite structure into metakaolin with amorphous structure, which has high pozzolanic activity. In the metastable state of metakaolin and other amorphous silicon aluminum compounds by alkaline activator and hardening agent, silicon aluminum oxygen compounds experienced a process from depolymerization to polymerization, the formation of some natural minerals in the crust similar to the aluminum silicate network structure. The geopolymeric cement has the link structure of organic polymer, but its basic structure is inorganic silicon oxygen tetrahedron and aluminum oxygen tetrahedron, in which the negative charge is balanced by cations such as alkali metal and alkaline earth metal.

 

2. Concrete admixture

Metakaolin is kaolin (Al2O3·2SiO2·2H2O) Anhydrous aluminum silicate formed by dehydration at an appropriate temperature (500-900°C) (Al2O3·2SiO2White powder, average particle size 1-2 μm,SiO2and Al2O3Content above 90%, especially Al2O3higher content. The arrangement of atoms in metakaolin is irregular, showing a thermodynamic metastable state, which has strong pozzolanic activity. Metakaolin is easy to react with cement hydration products CH and water to form hydration products, mainly CSH gel, calcium aluminate hydrate and calcium sulphoaluminate hydrate, so it is widely used in concrete admixture to replace silica fume.

 

3. Paint and coating

The main mineral raw materials used in the paint industry are calcium carbonate, talc, titanium dioxide and calcined kaolin. Because kaolin has excellent properties such as chemical inertness, strong covering ability, low cost and high whiteness, calcined kaolin acts as filler and pigment substitute in paint, which can not only control the demand of expensive fuel, but also reduce the production cost. For calcined kaolin, in addition to the above advantages, there are many characteristics: irregular shape, strong optical properties, pigment volume concentration and high oil absorption, wear resistance, not easy to aging, and hiding power is also very high.

In the paint industry, its main use is to replace white pigments, especially titanium dioxide; in addition, the particles and types are corresponding to each other, different types of paint with different particles and types of kaolin. For example, the use of coarse particles of calcined kaolin in dull or flat paint; shiny paint requires relatively fine particles of calcined kaolin, and the use of fine-grained kaolin opaque, anti-corrosion characteristics, can also be made of latex materials.

Material, kaolin, calcined, mineral, cement, paint, structure, kaolinite, particle, material

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