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Yuan Lei's Little Knowledge | Performance Characteristics of Kaolin

Release time:

2024-01-29 09:34

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.

The wide range of uses of kaolin is inseparable from its excellent physical and chemical properties. Pure kaolin has high whiteness, soft and easy to disperse and suspend in water, good plasticity and high bonding, excellent electrical insulation properties and good acid solubility, very low cation exchange capacity, high refractoriness and other physical and chemical properties.

 

 

01Color

White or nearly white, with a maximum whiteness of more than 95%. Whiteness is one of the main parameters of kaolin process performance, high purity kaolin is white. The whiteness of kaolin is divided into natural whiteness and whiteness after calcination. For ceramic raw materials, the whiteness after calcination is more important, and the higher the whiteness of calcination, the better the quality.

 

02Hardness

The hardness of soft kaolin is generally 1-2, and that of hard kaolin sometimes reaches 3-4.

 

03Granular and granular attitude

Particle size distribution refers to the proportion of particles in natural kaolin in a given series of different particle ranges. The particle size distribution of kaolin is usually 0.2-5 μm, and its particle size has a great influence on its plasticity, mud viscosity, ion exchange capacity, molding performance, drying performance and sintering performance. Kaolin ore requires technical processing, whether it is easy to process to the fineness required by the process has become one of the criteria for evaluating the quality of the ore. Various industrial sectors have specific particle size and fineness requirements for kaolin for different uses.

 

 

04plasticity

The clay formed by the combination of kaolin and water can be deformed under the action of external force. After the external force is removed, it can still maintain the nature of this deformation, that is, plasticity. The main factors affecting the plasticity of kaolin are: particle size, cation exchange capacity, particle morphology, impurity content.

 

05Sinterability

The sintering of kaolin is one of the important process properties that must be possessed in the manufacture of ceramic products. The so-called sintering refers to when the object is heated to a certain temperature, due to the fusible material generated by the liquid phase filling in the gaps between the unmelted particles, by its surface tension to reduce the porosity, density, volume shrinkage, thus becoming dense, hard performance. When the porosity decreases to the minimum value and the density reaches the maximum value, the state is called the sintered state, and the corresponding temperature is called the sintering temperature.

 

06Dispersion

Kaolin is easily dispersed and suspended in water, and can form a suspension with good stability.

 

 

07Electrical insulation

High quality kaolin has good electrical insulation, the use of this property can be used to make high frequency porcelain, radio porcelain. The level of electrical insulation performance can be measured by its resistance to electrical breakdown.

 

08chemical stability

Kaolin has strong acid resistance, but its alkali resistance is poor. The use of this property can be used to synthesize molecular sieves.

 

09Cation Exchange Capacity (CEC)

The cation exchange capacity of kaolin is generally 0.03-0.05mmol/g.

 

 

10 refractoriness

The refractoriness is related to the chemical composition of kaolin. The refractoriness of pure kaolin is generally about 1700 ℃. When the content of hydromica and feldspar is high, and the content of potassium, sodium and iron is high, the refractoriness is reduced, and the refractoriness of kaolin is not less than 1500 ℃.

 

11interaction with organic matter

Kaolin can interact with many polar organic molecules, such as formamide, acetamide, urea, etc. to produce kaolin-polar organic molecule chimeric complexes. Organic molecules can enter the interlayer domain and bond with the two surfaces of the structural layer by hydrogen bonding. As a result, the thickness of the structural unit layer of kaolin is increased, and the surface properties of kaolin, such as hydrophilicity, are changed.

Kaolin, properties, refractoriness, sintering, particle, plasticity, properties, cation, particle size

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