In the production of carbon, the commonly used raw mate […]
In the production of carbon, the commonly used raw materials can be divided into solid carbonaceous raw materials and binders and impregnating agents. Solid carbonaceous materials include petroleum coke, pitch coke, metallurgical coke, anthracite, natural graphite and graphite. The binder and impregnating agent include coal tar pitch, coal tar, eucalyptus oil and synthetic resin. In addition, some auxiliary materials such as quartz sand, metallurgical coke and coke breeze are used in the production. Some special carbon and graphite products (such as carbon fiber, activated carbon, pyrolytic carbon and pyrolytic graphite, glassy carbon) are used to produce other special raw materials.
Calcination: What is calcination? Which materials need to be calcined?
The process of heat treatment of a carbonaceous raw material under high temperature (1200-1500 ° C) under air-insulated conditions is called calcination. Calcination is the first heat treatment process for carbon production. Calcination causes a series of changes in the structure and physicochemical properties of various carbonaceous materials.
Both anthracite and petroleum coke contain a certain amount of volatiles and require calcination. The coking temperature of asphalt coke and metallurgical coke is relatively high (above 1000 °C), which is equivalent to the temperature of the calciner in the carbon plant. It can be no longer calcined, just dry the water. However, if pitch coke and petroleum coke are used in combination before calcination, they should be fed to the calciner for calcination together with petroleum coke. Natural graphite and carbon black do not require calcination.
Profile: What is the principle of extrusion?
The essence of the extrusion process is that after passing the paste through a certain shape of the nozzle under pressure, it is compacted and plastically deformed into a blank having a certain shape and size. The extrusion process is mainly the plastic deformation process of the paste.
The paste extrusion process is carried out in a chamber (or a paste bowl) and a circular-shaped nozzle. The hot paste in the loading chamber is pushed by the rear main plunger. The gas in the paste is forced to be continuously removed, the paste is continuously dense, and the paste moves forward. As the paste moves in the cylindrical portion of the chamber, the paste can be considered to be a steady flow, with each layer of particles moving substantially in parallel. When the paste enters the extrusion nozzle portion with arc deformation, the paste adhering to the nozzle wall is subjected to a large frictional resistance, the material layer begins to bend, and the inside of the paste produces different advancement speeds, and the inner layer paste Advance advancement of the material leads to uneven density of the product along the radial direction, thus causing internal stress caused by different flow rates of the inner and outer layers in the extrusion block. Finally, the paste enters the linear deformation portion and is extruded.
Roasting: What is roasting? What is the purpose of roasting?
The calcination is a heat treatment process in which the green product after pressing is heated in a protective medium in a heating furnace under a condition of insulating air at a certain heating rate.
The purpose of roasting is to:
(1) Excluding volatile matter A product using coal tar pitch as a binder generally discharges about 10% of volatile matter after calcination. Therefore, the firing yield is generally below 90%.
(2) The binder coking raw product is calcined according to certain process conditions to coke the binder, forming a coke network between the aggregate particles, and firmly bonding all aggregates of different particle sizes to make the product have certain Physical and chemical properties. Under the same conditions, the higher the coking rate, the better the quality. Generally, the coke residual carbon ratio of the medium temperature asphalt is about 50%.
(3) Fixed geometric form The green product is softened and the binder migrates during the roasting process. As the temperature increases, a coking net forms, causing the article to become rigid. Therefore, the temperature rises again and its shape does not change.
(4) Reducing the resistivity In the roasting process, the resistivity is greatly reduced due to the elimination of volatile matter, the formation of a coke grid by coking of the asphalt, the decomposition and polymerization of the asphalt, the formation of a large hexagonal carbon ring planar net, and the like. The resistivity of the raw product is about 10000×10-6 Ω·m, and after calcination, it is reduced to 40--50×10-6 Ω·m, which is called a good conductor.
(5) Further shrinkage of the volume After calcination, the diameter of the product shrinks by about 1%, the length shrinks by about 2%, and the volume shrinkage is 2-3%.
Impregnation: Why do you want to impregnate carbon products?
The pore size of the green product after compression molding is very low. However, after the green product is calcined, part of the coal tar is decomposed into gas during the roasting process, and the other part is coked into pitch coke. The volume of the resulting pitch coke is much smaller than the volume originally occupied by the coal leaching. Although it shrinks slightly during the roasting process, many irregular pores of different pore sizes are formed inside the product. For example, the total porosity of the graphitized article is generally 25-32%, and the total porosity of the carbon article is generally 16-25%. Due to the existence of a large number of pores, it will inevitably have a certain impact on the physical and chemical properties of the product. In general, the porosity of the graphitized article is increased, the bulk density is lowered, the electrical resistivity is increased, the mechanical strength is decreased, the oxidation rate is accelerated at a certain temperature, the corrosion resistance is also deteriorated, and the gas and the liquid are more easily penetrated.
Impregnation is a process that reduces product porosity, increases density, increases compressive strength, reduces finished resistivity, and changes the physical and chemical properties of products.