Kaolin process characteristics and main uses (2)

8 . Burning shrinkage

The firing shrinkage refers to a series of physicochemical changes ( dehydration, decomposition, mullite formation, melting of fusible impurities to form a glass phase filled in the space between the particles, etc. ) during the calcination of the dried kaolinite . The performance that causes the product to shrink is also divided into two types: line shrinkage and body shrinkage. Like the drying shrinkage, the firing shrinkage is too large, which tends to cause cracking of the green body. Further, during firing, if mixed with a large billet of quartz, the crystal transformation will occur (→ hexagonal constituents), to expand its volume, will produce anti-shrinkage.

9 . Fire resistance

Fire resistance refers to the ability of kaolin to resist high temperatures from melting. The temperature is called refractoriness when softening occurs at high temperature and melting begins. It can be directly measured by standard temperature measuring cone or high temperature microscopy, and M can also be used. A. The Belzburgov empirical formula is used for calculation.

Refractoriness t( °C )=[360+Al 2 O 3 -R 2 O]/0.228

Formula: Al 2 O 3 to SiO 2 and Al 2 O 3 Results and analysis of 100 Al 2 O 3 wherein the mass percentage; R 2 O of SiO 2 and Al 2 O 3 analysis results is 100 The percentage by mass of other oxides.

Calculate the error of refractoriness by this formula 50 °C Within.

The degree of refractoriness is related to the chemical composition of kaolin. The refractoriness of pure kaolin is generally 1700 °C Left and right, when the content of hydromica and feldspar is high, and the content of potassium, sodium and iron is high, the refractoriness is lowered, and the refractoriness of kaolin is at least not less than 1500 °C . The industrial sector stipulates that the R 2 O content of the refractory material is less than 1.5 - 2% and the Fe 2 O 3 is less than 3% .

10 . Suspension and dispersion

Suspension and dispersibility refer to the ability of kaolin to be dispersed in water and difficult to precipitate. Also known as deflocculation. Generally, the finer the particle size, the better the suspension. Kaolin used in the enamel industry requires good suspension. Generally, the suspension performance of a sample dispersed in water is determined by a settling time for a certain period of time.

11 . Optional

Optional means that the kaolin ore is hand-selected, machined and chemically treated to remove harmful impurities and to achieve the desired quality of the industry. The selectivity of kaolin depends on the mineral composition, state of occurrence, particle size, etc. of harmful impurities. Quartz, feldspar, mica, iron, titanium minerals, etc. are all harmful impurities. Kaolin mineral processing mainly includes projects such as sand removal, iron removal and sulfur removal.

12 . Ion adsorption and exchangeability

Kaolin has the property of adsorbing various ions and impurities from the surrounding medium, and has weak ion exchange properties in the solution. The pros and cons of these properties are mainly determined by the main mineral components of kaolin, as shown in Table 2 .

Table 2   Cation exchange capacity of different types of kaolin

Mineral composition characteristics

Cation exchange capacity

Kaolinite

2 — 5mg/ 100g

Eloline-based

13mg/ 100g

Containing organic matter (ball soil)

10 — 120mg/ 100g

 

13 . Chemical stability

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

14 . Electrical insulation

High-quality kaolin has good electrical insulation, and it can be used to make high-frequency porcelain and radio porcelain. The electrical insulation performance can be measured by its electrical breakdown resistance.

( 2 ) Main uses: See Table 3 .

 

Table 3    The main use of kaolin

Application field

The main purpose

Ceramic industry

The main raw materials for the ceramic industry, used in the production of daily-use ceramics, construction and sanitary ceramics, electric porcelain, chemical corrosion-resistant ceramics, arts and crafts ceramics and special ceramics, etc.

Paper industry

Used in paper fillers and coatings to improve paper density, whiteness and smoothness, improve printing performance and reduce papermaking costs

Refractory

And cement industry

Refractoriness higher than or equal to 1770 ° C Pure kaolin can be used to smelt enamel and laboratory enamel for optical glass and glass fiber , low-grade kaolin refractory brick, enamel, refractory mud, iron plug and fired white cement.

Rubber industry

Producing reinforcing and fillers to improve the mechanical strength and acid resistance of rubber, improve product performance and reduce costs

Petroleum and chemical industry

Manufactured by high-performance adsorbents, instead of chemical synthetic molecular sieves, used as petroleum cracking catalysts

Medicine, textile industry

Coating as a pharmaceutical, an adsorbent, additives, bleaching agents, production of detergents, cosmetics, pencil lead, paint, paint fillers

agriculture

Used as a carrier for fertilizers, pesticides and pesticides

Cutting-edge technology

High-quality kaolin is required for atomic reactors, jets, rocket fuel cells, and nozzles.

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