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Yuan Lei tells you | The characteristics of kaolin

Release time:

2024-01-29 09:38

 

Yuan Lei tells you | The characteristics of kaolin

 

Pure kaolin has high whiteness, soft, easy to disperse and suspend in water, good plasticity, high adhesion and excellent electrical insulation properties;It has good anti-acid solubility, low cation exchange capacity, good fire resistance and other physical and chemical properties.Therefore, kaolin has become a necessary mineral raw material for dozens of industries such as papermaking, ceramics, rubber, chemical industry, paint, medicine and national defense. Kaolin is widely used in paper industry.There are two main areas, one is the filler used in the papermaking (or papermaking) process, and the other is the pigment used in the surface coating process.

 

 

 

Chemical formula

 

Al2O3-2SiO2-2H2O

 

 

particle size distribution

 

Particle size distribution refers to the proportion (expressed as a percentage) of particles in natural kaolin within a given series of different particle sizes (expressed as a mesh with millimetres or micrometres).The particle size distribution characteristics of kaolin is of great significance to the ore's washability and process application, 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.For example, the United States requires 90-95% of kaolin used as a coating with a content of less than 2μm, and 78-80% of papermaking fillers less than 2μm.

 

plasticity

 

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.Plasticity is the basis of the forming process of kaolin in ceramic bodies, and it is also the main technical index of the process.The plasticity index and plasticity index are usually used to express the size of plasticity.Plasticity index refers to the liquid limit water content of kaolin mud minus the plastic limit water content, expressed as a percentage, I .e. W plasticity index = 100(W liquid limit-W plasticity limit).The plasticity index represents the forming performance of kaolin clay. The load and deformation size of the clay ball when it is crushed under pressure can be directly measured by a plasticity meter. The higher the plasticity index, the better the forming performance.The plasticity of kaolin can be divided into four levels.

plasticity strength plasticity index plasticity index

Strong plasticity> 153.6

Medium plasticity 7-152.5-3.6

Weak plasticity 1-7<2.5

Non-plastic <1

 

Combination

 

Binding refers to the combination of kaolin and non-plastic raw materials to form plastic mud and has a certain dry strength performance.The determination of binding ability is to add standard quartz sand to kaolin (its mass composition is 0.25-0.15 grain fraction accounts for 70%,0.15-0.09mm grain fraction accounts for 30%).It can still maintain the plastic clay mass when the highest sand content and the flexural strength after drying to judge its level, the more mixed sand, the stronger the binding capacity of this kaolin.Usually, the binding ability of kaolin with strong plasticity is also strong.

 

Viscosity and thixotropy

 

Viscosity refers to a feature that hinders the relative flow of a fluid due to internal friction. Viscosity is used to express its size (internal friction acting on 1 unit area), and the unit is Pa · s.Viscosity is generally measured using a rotational viscometer, measured at rotational speed in a kaolin slurry containing 70% solids.In the production process, viscosity is of great significance. It is not only an important parameter in the ceramic industry, but also has a great influence on the paper industry.According to the data, kaolin is used as a coating abroad, and the viscosity is required to be about 0.5Pa · s when coating at low speed and less than 1.5Pa · s when coating at high speed.

Thixotropy refers to the characteristics of mud that has been thickened into a gel and no longer flowing, which becomes fluid after being forced, and gradually thickens into its original state after being stationary.The size is expressed as a thickening coefficient, which is measured by an outflow viscometer and a capillary viscometer.

 

The viscosity and thixotropy are related to the mineral composition, particle size and cation type in the mud. Generally, the montmorillonite content is high, the particles are fine, and the exchange cation is mainly sodium, and its viscosity and thickness coefficient are high.Therefore, the process is commonly used to add plastic clay, improve fineness and other methods to improve its viscosity and thixotropy, with the increase of diluted electrolyte and moisture and other methods to reduce it.

 

Drying performance

 

Drying performance refers to the performance of kaolin mud in the drying process.Including drying shrinkage, drying strength and drying sensitivity.

Drying shrinkage refers to the shrinkage of kaolin mud after dehydration and drying.Kaolin mud is generally dehydrated and dried at a temperature of 40-60 ℃ at most not more than 110 ℃. Due to the discharge of water, the particle distance is shortened, and the length and volume of the sample will shrink.Drying shrinkage line shrinkage and body shrinkage, expressed as the percentage of length and volume change after kaolin mud is dried to constant weight.The drying line shrinkage of kaolin is generally 3-10%.The finer the particle size, the larger the specific surface area, the better the plasticity, and the greater the drying shrinkage.The same type of kaolin, due to the different blending water, the shrinkage is also different, more, shrinkage.In the ceramic process, the drying shrinkage is too large, and the green body is prone to deformation or cracking.

Drying strength refers to the flexural strength of the mud after drying to constant weight.

 

Drying sensitivity refers to the degree of difficulty that may cause deformation and cracking tendency when the green body is dried.The sensitivity is large, and it is easy to deform and crack during the drying process.Generally, kaolin with high drying sensitivity (drying sensitivity coefficient K>2) is easy to form defects;The lower one (drying sensitivity coefficient K<1) is safer in drying.

 

 
 
 
 
 
 

 

 

Tell, kaolin, dry, plasticity, shrinkage, properties, said, viscosity, binding, particle size

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