The porosity of the graphite product after pressing is very low. However, after these products are roasted, the part of the coal tar pitch decomposed into gas during the firing process will escape, and the other part will be coked to produce pitch coke. The volume of pitch coke produced cannot be less than the volume originally occupied by coal pitch. Although it shrinks slightly during the roasting process, many irregular and small pores with different pore sizes are still formed inside the product.
For example, the total porosity of graphitized products is 25-32%, and the total porosity of carbonaceous products is 16-25%. Due to a large number of pores, it is bound to have a certain impact on the physical and chemical properties of the product.
As far as graphite electrode manufacturers are concerned, the porosity of graphite electrodes increases, its relative volume density continues to decrease, the electrical resistivity rises, and the mechanical design strength can be reduced. The oxidation reaction speed at a certain temperature develops faster, and the corrosion resistance also deteriorates. , Gas and liquid are easier to penetrate.
Impregnation is the process of reducing the cell size of the graphite electrode to increase the density, increase the compressive strength, and reduce the resistivity of the finished graphite electrode. The process of changing the physical and chemical properties of graphite electrodes.