1. Overview of Spodumene
There are three variants of spodumene (Li2O3·Al2O3·4SiO2) crystals, namely α-spodumene, β-spodumene, and γ-spodumene. α-spodumene is usually called spodumene, which is a low-temperature stable variant; β-spodumene is a stable high-temperature variant; γ-spodumene is a high-temperature metastable variant, which can become β- Spodumene. The structure of β-spodumene allows SiO2 to enter the crystal lattice to form β-spodumene solid solution, and with the increase of SiO2 content in the structure. Its thermal expansion coefficient tends to decrease.
2. Preparation process of spodumene ceramics
(1) Pre-burning of spodumene
The spodumene that exists in nature exists in the form of α-spodumene, and the appearance is white, off-white, columnar or fibrous, with glass luster, hardness 6. 5-7, density 3. 03-3. 22g/cm3. Since α-spodumene is converted into high-temperature stable β-spodumene, a volume expansion of about 30% occurs, so the spodumene must be calcined in advance, and the calcination is stable at about 1100°C.
Spodumene
(2)The formula of spodumene ceramics
Spodumene ceramics often use spodumene-quartz-kaolin as the formula system, and the final substance has different expansion coefficients according to the amount of spodumene added.
(3) Forming of spodumene ceramics
The forming method of spodumene ceramics can adopt the forming method of ordinary ceramics, that is, grouting forming, plastic forming, semi-dry pressing. When grouting and plastic molding are used, sufficient binding clay is required in the formula, otherwise the green substance is easy to crack during the drying process. To reduce cracking, organic additives can also be added to the green substance.
(4) Sintiring
The sintiring range of spodumene ceramics is relatively narrow, generally only about 10°C, so reasonable furnaces such as pusher kilns and shuttle kilns should be used.
Kiln instead of tunnel kiln. In addition, oxidizing atmosphere should be used for firing to reach the highest firing temperature, and rapid cooling should be used to prevent the crystal grains from growing too much.
3. Properties and applications of spodumene ceramics
Spodumene ceramics have a very low thermal expansion coefficient and excellent thermal shock resistance, so they are widely used in kiln furniture, induction heating components (such as microwave oven gaskets), high temperature fixtures, resistance wire coils, high voltage transmission insulators, and astronomical telescope mirror blanks , High temperature radiation baffle, heat-resistant tableware for household use, and thermocouple protection tube, etc. Spodumene ceramics can be made into zero-expansion or slightly positive expansion ceramics. They are used in impeller fins, jet engine parts, nozzle linings, internal combustion engine parts, and high-precision electronic components with stable dimensions.
Spodumene ceramics have high temperature chemical stability and can be used in metal pouring barrels, laboratory combustion boats and combustion tubes, acid-resistant leaching tanks, etc.
