Graphite plates refer to various types of graphite plates made from different types of coke or coal particles as aggregates, and coal tar pitch as a binder. After pressure forming, the porosity of the products is very low. However, after calcination, some of the coal tar pitch is decomposed into gas during the calcination process, and the other part is coking into asphalt coke.
The volume of generated asphalt coke is much smaller than the original volume occupied by coal tar pitch. Although the product shrinks slightly during calcination, many irregular and small pores with varying pore sizes are still formed inside the product. For example, the total porosity of graphite plates is generally 25-32%, and the total porosity of carbon products is also 16-25%. The presence of a large number of pores will inevitably have some impact on the physical and chemical properties of the product.
Generally speaking, the porosity of a product increases, the specific gravity (density) decreases, the specific resistance increases, the mechanical strength decreases, the oxidation rate accelerates at specific temperatures, the corrosion resistance also deteriorates, and gases or liquids are more likely to penetrate. Immersion (also known as immersion) is a process of reducing product porosity and improving product quality.
There are usually several products that need to be impregnated: small-sized graphite electrodes and joint blanks, and various specifications of graphite anodes should be impregnated. These products require high density and strength, as well as low specific resistance. Therefore, the roasted semi-finished products are first impregnated with coal tar pitch, which is then graphitized. After being impregnated with coal tar pitch once, the specific gravity of the finished product can range from about 1.55 g/cm3 to 1.85 g/cm3.