What are the Raw Materials for Graphite Electrodes?

Graphite Electrodes use petroleum coke and needle coke as aggregate and coal pitch as a binder. It is a kind of high-temperature-resistant graphite conductive produced by a series of processes such as kneading, moulding, baking, impregnation, graphitization, and mechanical processing material. What are the raw materials for graphite electrodes? Let's find out with most of the Graphite Electrode Manufacturer.

The raw materials for producing graphite electrodes are petroleum coke, needle coke and coal pitch. Petroleum coke is a combustible solid product obtained after coking of petroleum residue and petroleum pitch. The colour is black and porous, the main element is carbon, and the ash content is very low, generally below 0.5%. Petroleum coke belongs to the class of easily graphitizable carbon. Petroleum coke has a wide range of uses in the chemical and metallurgical industries and is the main raw material for the production of artificial graphite products and carbon products for electrolytic aluminium. Petroleum coke can be divided into two types: raw coke and calcined coke according to the heat treatment temperature. The former is a coke obtained by delayed coking. It contains a large amount of volatiles and has low mechanical strength. Calcined coke is obtained by calcining raw coke. Most refineries in China only produces coke, and calcination operations are mostly carried out in carbon plants.

Needle Coke can be divided into high sulphur coke (more than 1.5% sulphur), medium sulphur coke (0.5% -1.5% sulphur), and low sulphur coke (less than 0.5% sulphur). Graphite electrodes and other artificial graphite products are generally produced using low sulphur coke.

Graphite Electrodes

Needle coke is a kind of high-quality coke with obvious fibrous texture, extremely low thermal expansion coefficient and easy graphitization. When the coke block is broken, it can be split into slender strip-like particles (the aspect ratio is generally above 1.75). An anisotropic fibrous structure can be observed under a polarizing microscope, so it is called acicular focal.

The anisotropy of the physical and mechanical properties of acicular coke is very obvious. It has good electrical and thermal conductivity parallel to the long axis of the particles and has a low thermal expansion coefficient. During extrusion moulding, the long axis of most particles is arranged in the direction of extrusion. Therefore, acicular coke is a key raw material for manufacturing high-power or ultra-high-power graphite electrodes. The graphite electrode produced has low resistivity, small thermal expansion coefficient, and good thermal shock resistance. Needle coke is produced using petroleum residue as a raw material. Oil-based needle coke and coal-based needle coke produced from refined coal pitch raw materials. Coal tar is one of the main products of deep processing of coal tar. It is a mixture of multiple hydrocarbons. It is a black high viscosity semi-solid or solid at normal temperature, without a fixed melting point. It softens after heating and then melts, with a density of 1.25-1.35g / cm3. According to its softening point, it can be divided into a low temperature, medium-temperature and high-temperature asphalt. The yield of medium temperature asphalt is 54-56% of coal tar. The composition of coal tar is extremely complicated, which is related to the properties of coal tar and the content of heteroatoms and is also affected by the coking process system and the processing conditions of coal tar. There are many indicators to characterize coal asphalt, such as asphalt softening point, toluene insoluble (TI), quinoline insoluble (QI), coking value and coal tar rheology.

Coal tar is used as a binder and impregnant in the carbon industry, and its performance has a great impact on the production process and product quality of carbon products. As binder asphalt, moderate-temperature or moderate-temperature modified asphalt with a moderate softening point, high coking value and high beta resin is generally used. As the impregnant, medium-temperature asphalt with a lower softening point, low QI, and good rheological properties.