1? What is the general technological process of producing high purity graphite? The specific content can be found on the website of China Powder Science and Technology Network.
The main production process in high purity graphite is shown in figure 1. Obviously, the production process of high purity graphite is different from that of graphite electrode. High purity graphite needs raw materials with isotropic structure, needs to be ground into finer powder, needs to apply isostatic pressing technology, and has a long baking cycle. In order to achieve the ideal density, it needs many impregnation-baking cycles, and the graphitization cycle is much longer than that of ordinary graphite.
1. 1? raw material
The raw materials for producing high purity graphite include aggregate, binder and impregnant. Aggregates are usually needle-like petroleum coke and pitch coke. This is because needle-like petroleum coke has the characteristics of low ash content (generally less than 1%), easy graphitization at high temperature, good electrical and thermal conductivity and small linear expansion coefficient. At the same graphitization temperature, the graphite obtained from pitch coke has higher resistivity and higher mechanical strength. Therefore, in general, besides petroleum coke, pitch coke is also used to improve the mechanical strength of products. Coal tar pitch is usually used as binder, which is the product of coal tar distillation. It is a black solid at room temperature and has no fixed melting point.
1.2? Calcination/purification
Calcination is to heat all kinds of solid carbon raw materials at high temperature under the condition of isolating air. The selected aggregate contains moisture, impurities or volatiles in its internal structure to varying degrees due to its different coking temperature or geological age of coal formation. These substances need to be removed in advance, otherwise the product quality and service performance will be affected. The selected aggregate should be calcined or purified.
1.3? crocus
Although the particle size of solid materials used in graphite production has decreased after calcination or purification, the particle size is still large, fluctuating and the composition is uneven. It is necessary to crush the aggregate size to the batching requirements.
1.4? Mixing and kneading
The ground powder needs to be mixed with coal tar pitch binder according to a certain proportion, and put into a heating kneader for kneading, so that the materials are evenly distributed.
1.5? Forming/shaping
There are four main methods: extrusion molding (Figure 2a), compression molding (Figure 2b), vibration molding and isostatic pressing molding (Figure 2c).
1.6? roast
Molded carbon products must be roasted, that is, the pressed green body must be heat-treated (about 65438 0000℃) under the condition of air isolation, so that the binder can be carbonized into binder coke.
1.7? suck up
The purpose of impregnation is to fill impregnating agent, such as molten asphalt, into the micropores formed in the product during roasting and the original openings of aggregate coke particles, so as to improve the bulk density, conductivity, mechanical strength and chemical corrosion resistance of the product.
1.8? graphitization
Graphitization refers to the high-temperature heat treatment process in which non-graphitic carbon with thermodynamic instability is transformed into graphitic carbon through thermal activation.