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Yuan lei small class | kaolin, how much do you know about it?

Release time:

2024-01-29 09:36

 

Yuan lei small class | kaolin, how much do you know about it?

 

CLASSIFICATION OF KAOLIN

 

The naturally produced kaolin ore, according to its quality, plasticity and sandy (quartz, feldspar, mica and other minerals particle size> 50 microns) content, can be divided into coal kaolin, soft kaolin and sandy kaolin three types.

 

The nature of different resources basically determines the direction of the industry that the resources can be suitable for development. In general, the domestic coal kaolin (hard kaolin), more suitable for the development of calcined kaolin, mainly used in various uses of filler. Calcined kaolin due to high whiteness, also have applications in papermaking, and for the production of high-grade coated paper, expensive. However, because the calcined soil mainly increases the whiteness, it is generally not alone, and the amount used in papermaking is less than that of washed soil. Non-coal-bearing kaolin (soft kaolin and sandy kaolin), mainly used in paper coatings and ceramics industry. The crystal structure of non-coal kaolin is mainly divided into single plate (diameter thickness ratio is 8:1), tubular and laminated plate.

 

Among them, kaolin (stone) with single sheet structure represented by Maoming Basin can be directly applied to paper coating by simple process treatment, with relatively low processing cost and high added value; Kaolin (stone) with tubular structure represented by Longyan in Fujian Province can be applied to ceramic materials and refractory materials; It is inherently insufficient, but it can also be used for papermaking after peeling, and the cost is slightly higher than that of Maoming soil. Moreover, according to expert analysis, the limitation of natural quality makes the viscosity concentration of Hepu soil low. Under the current technical conditions, it cannot be used for high-grade paper coatings after processing.

 

 

It should be noted that the division of labor in this use is not absolute either. With the progress of technology, the differences in the natural endowments of kaolin resources can be smoothed by technological progress. Of course, the possibility and feasibility of technology are two completely different concepts, and the feasibility of technology does not yet represent the value of industrial applications. In the practical application of industry, there is a problem of performance-price ratio, and the cost must have an advantage in order to have application value. The current relative distinction in this use is premised on the prior art. This is also an important reason why Maoming kaolin has an advantage at present.

 

dispersion of kaolin

 

The high-territory particles are pseudo-flake hexagonal structure, and all kaolin suspensions are easy to agglomerate at low PH value (PH = 4), and the agglomeration is in the state of edge facing the surface. Generally, when the pH of kaolin is 7.3 acidic, the side is positively charged and the surface is negatively charged. When the pH value is greater than 9.0, the entire kaolin surface is negatively charged, resulting in mutual repulsion, in a certain dispersion state. Generally, kaolin is dispersed in a suspended aqueous solution, and a certain amount of dispersant needs to be added, and a certain amount of NaOH is added to make the PH value reach 7.0-8.0 to achieve the best dispersion effect. If it is mixed with other pigments, it is necessary to take into account. The amount of dispersing agent used depends on the form of the kaolin, for example, spray dried kaolin, which has residual dispersing agent on the surface, so that a relatively small amount of dispersing agent may be used as compared to kaolin having a lower pH. Kaolin dispersion in the state of high-speed mixing feeding, feeding after the completion of the mixing should be a certain time, in order to ensure the dispersion effect, the general dispersion material temperature can basically reflect the length of the dispersion time, dispersion time is long, the relative dispersion effect is better. The power of the dispersion equipment should be suitable for the variety of coated kaolin, such as calcined soil is not dispersed as hard as standard water and soil, because it will break the agglomerate. The dispersed kaolin must be sieved, and the mesh can be between 120 mesh and 180 mesh. It should be noted that reagglomeration may occur when the dispersion is left for a period of time, and a slight addition of dispersant is usually used to compensate for these effects.

 

The more effective dispersants for dispersing kaolin are sodium hexametaphosphate and sodium pyrophosphate; the commonly used dispersants generally use sodium polyacrylate, and the effect of different suppliers of dispersants is very different.

 

 

Viscosity and viscosity concentration of kaolin

 

Viscosity refers to a feature that prevents 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(IS unit) or P(cgs unit). Thixotropy refers to the characteristics of mud that has been thickened into a gel and no longer flowing into a fluid after being forced, and then gradually thickens into the original gel after being stationary. 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 the fineness and other methods to improve its viscosity and thixotropy, by increasing the diluted electrolyte and moisture and other methods to reduce its viscosity and thixotropy.

 

The viscous concentration of porcelain clay is also an important index for evaluating porcelain clay. The viscous concentration refers to the solid concentration of the coating when the temperature is 25 ℃ and the viscosity reaches 500mpa.s. Modern coating equipment has more and more strict requirements for high solid content and low viscosity coatings. The higher the viscous concentration, the more conducive to the preparation of low viscosity and high concentration coatings. The viscous concentration of good porcelain clay can reach 74%, and the viscous concentration of domestic kaolin can also reach more than 71%.

 

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