As the raw material of the binder, when the electrode paste is self-baked and sintered, the remaining coking residue can increase the strength and uniform texture of the electrode. The best binders are coal pitch and coal tar.
1. Coal tar
Coal tar is a group of fractions with a lower temperature than coal tar pitch. It is a viscous liquid with a color ranging from dark brown to black and a relative density of 1.05-1.25. The quality of tar mainly depends on the temperature conditions of coking and the structure of the furnace. In the furnace of the same structure, the temperature conditions are the same, and the tar with the same composition and physical properties can also be obtained when coking the mixed coal of different composition. The coal tar mentioned in this section is used to adjust the softening point of the electrode paste in a closed furnace after heat treatment. 2. Coal pitch
Asphalt is a black shiny solid substance with a relative density of 1.245-1.299. When the distillation temperature is above 360°C, the residue left after extracting other fractions in the tar is pitch. According to the softening point, bitumen can be divided into soft bitumen, oily medium bitumen of 40-50℃, hard bitumen of 65-75℃, higher than 80℃. The discussion in this section is medium pitch.
China Asphalt’s entry standard is
Softening point Mercury method ℃ 65-75℃
Free carbon C 18-25%
Moisture W ≯ 5%
Ash content ≯ 0.5%
Volatile content 55-70%
The moisture of asphalt includes two parts, which are mechanically suspended and absorbed. After heat treatment for several days and nights above 130°C, the moisture is removed and expansion is reduced before it can be used for production. The composition of asphalt contains free carbon, which is brought into the asphalt from the tar, and the other part is decomposed by polymer compounds during the distillation of the tar. The most precious part of pitch and tar is the coking part, that is, the bonded coke. By removing the free carbon from the coking residue, the bonded coke can be obtained.
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