ABC of graphite electrodes (2) – what are electrodes made of?

this is part 2 of our series. As promised, the first article covers the raw materials of graphite electrodes.

Raw materials of graphite electrodes

We only mention here the raw materials which become a part of the electrode end product. Apart from those we can mention auxiliary materials such as Quartz Sand for the baking process. The raw materials that make up an electrode recipe are as follows.

Petroleum coke & needle coke

Petroleum coke is produced using the route of crude oil vacuum distillation and delayed coking. Needle coke is a highly crystalline petroleum coke type with clear striped texture with directionality to allow for high thermal expansion coefficient and electrical conductivity. Therefore, needle coke is the most ideal material for the production of graphite electrodes.  Interesting for us is the ratio of petroleum coke and needle coke. In practice of electrode making, petroleum and needle coke contents have an inverse relationship: the lower the content of needle coke, the higher that of petroleum coke and vice versa. As we will see in the section about graphite electrode grading system, we can denote an electrode formula superior in quality, the higher. The leading manufacturers for needle coke by annual output are as follows: Seadrift coke LP (USA), Conoco Philips (Britain), Mizushima Ferroalloy Co., Ltd (Japan), Jinzhou CNPC (Jinzhou, China), Gaoqiao CNPC (Shanghai, China), Mitsubishi Chemical (Japan), Hongte (Shanxi, China), Sinosteel Anshan Research Institute of Thermo-energy Co., Ltd (Anshan, China)

Metallurgical coke

In the form of powder & particles, metallurgical coke is a coal with a low ash and sulfur content. It is beneficial to add this ingredient to increase hardness and decrease the release of burned ash during electrode use.

Coal tar pitch

Used during the kneading and the impregnation phases of the production process. When kneading, the liquid coal tar pitch is added to combine the otherwise loose particles to form a soft mass. Like metallurgical coke, it is produced from coal over the route coal -> coal tar -> coal tar pitch utilizing fractional distillation. For the impregnation stage (which is the production step between baking and graphitization; more on this process later), it is used to decrease the porosity by filling the many small holes inside the semi-finised electrode. Thereby, the product gains in density.

In the next article, we will be concerning ourselves with the question: how are graphite electrodes produced? We are going to focus on the production process overview.

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