Table 4 Â Sodium fluoride quality level ( GB4293-84 ) | |||||||
product | Chemical composition /% | ||||||
level | ≥ | ≤ | |||||
　 | NaF | H 2 O | SiO 2 | Acidity ( HF ) | Na 2 CO 3 | Sulfate SO 4 2- | Insoluble matter in water |
First level | 98 | 0.5 | 0.5 | 0.1 | 0.5 | 0.3 | 0.7 |
Secondary | 94 | 1 | 1 | 0.1 | 1 | 0.5 | 3 |
Third level | 84 | 1.5 | 　 | 0.1 | 2 | 2 | 10 |
5 Calcium Fluoride (CaF 2 ) Calcium fluoride is selected from natural fluorite . The selected particle size is 90% by 140 mesh, and 75% of it passes through 200 mesh. Calcium fluoride is an additive that is more common in the early application, and its chemical composition accounts for the following proportions:
CaF 2 SiO 2 A1 2 O 3 +F 2 O 3 H 2 O CaCO 3
>95% <1.4% <0.5% <0.5% <1.5%
6 Magnesium Fluoride (MgF 2 ) Magnesium fluoride is also an additive, but it is not commonly used, and it is used later than calcium fluoride. It is considered to be a good additive in improving electrolyte properties. The chemical composition requirements are as follows:
F Mg SiO 2 SO 4 2- R 2 O 3 H 2 O
>45% >32% <0.9% <1.5% <1.0% <1.0%
⑦ anode paste anode paste is fired next to or inserted into the socket of the anode material, the oxygen generated during electrolysis aluminum was anodized oxidative decomposition of the carbon anode is consumed as the electrolysis process due to the electrolysis process continues Therefore, the anode paste must be added periodically. The anode paste is consumed in large quantities, second only to alumina. After the anode paste is added into the side plug or the upper slot, the Joule heat generated by its own resistance and the heat supplied by the electrolyte are self-fired into a carbon anode, so the two anodes are called continuous self-baking carbon anodes. The aluminum industry uses carbon materials as electrodes because of its good electrical conductivity and sufficient strength, high temperature resistance, resistance to fluoride attack, and a wide range of sources and low cost. [next]
The anode paste is prepared in an anode paste workshop or a carbon factory. After calcination at 1250 ° C or higher, it is pulverized into petroleum coke or pitch coke or a mixture of two cokes with a certain particle size ratio, accounting for 28%-32 of the total amount. % of melt-kneading in kneading pitch pan or in a continuous kneader, mixed evenly poured into an iron or iron container model molding cooling (big and small size) or made into small clumps. The quality level of the anode paste is shown in Table 5.
Table 5 Â Anode paste quality level ( YS/T Â 284-1998 ) | ||||||
Brand | Ash /% | Resistivity / ( μ Ω· m ) | Compressive strength / ( N / m 2 ) | True density / ( g / cm 3 ) | Bulk density / ( g / cm 3 ) | CO 2 reactivity / [mg / (cm 2 · h) |
≤ | ≥ | ≤ | ||||
TY-0 | 0.35 | 70 | 29 | 2 | 1.4 | 80 |
TY-1 | 0.45 | 75 | 28 | 1.99 | 1.39 | 95 |
TY-2 | 0.6 | 80 | 27 | 1.98 | 1.38 | 110 |
TY-3 | 0.8 | 80 | 27 | 1.98 | 1.38 | 110 |
In addition to the common requirements listed in Table 5, the requirements for the side-by-slot anode paste and the upper-slot anode paste differ in terms of plasticity. The former requires a lesser flow of the anode paste, while the latter requires sufficient fluidity.
The anode block of the anode block is the anode in the prebaked bath. The performance depends on the quality of the raw paste and the quality of the forming and firing. Modern anode blocks are generally formed by vibration molding, and the molded product is sent to a ring roaster or other kiln for firing. Pre-baked anode blocks are called because they have been pre-baked before they are added to the cell. The quality requirements for the anode block are shown in Table 6.
Table 6 Â Prebaked anode block quality grade ( YS/T 285-1998 ) | |||||||
Brand | Ash /% | Resistivity / ( μ Ω· m ) | Thermal expansion rate /% | CO 2 reactivity / [mg / (cm 2 · h) | Compressive strength / ( N / m 2 ) | Bulk density / ( g / cm 3 ) | True density / ( g / cm 3 ) |
≤ | ≥ | ||||||
TY-1 | 0.5 | 55 | 0.45 | 45 | 32 | 1.5 | 2 |
TY-2 | 0.8 | 60 | 0.5 | 50 | 30 | 1.5 | 2 |
TY-3 | 1 | 65 | 0.55 | 55 | 29 | 1.48 | 2 |
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