“Under-burnt” calcined coke, due to insufficient calcination of the raw material, will lead to internal structural defects during subsequent graphitization, which in turn trigger irreversible defects such as cracks, uneven density, abnormal volume shrinkage, and performance degradation in graphitized products. A detailed analysis is as follows:
Direct Impact of Insufficient Calcination of Raw Materials
Calcination is a crucial step before graphitization, aimed at allowing volatile substances within the raw materials (such as petroleum coke and needle coke) to escape through high-temperature treatment, reducing impurity content, and forming an appropriate pore structure. If calcination is inadequate (i.e., “under-burnt”), a significant amount of volatile substances and unreacted impurities will remain in the raw materials. These residues will continue to decompose or react during subsequent graphitization, causing gas escape or chemical changes within the products, thereby leading to structural defects.
Irreversible Defects Generated During Graphitization
Crack Defects:
- Formation Cause: The residual volatile substances and impurities in under-burnt calcined coke rapidly decompose or react under the high temperatures of graphitization, generating a large amount of gas. This gas accumulates within the product and seeks escape paths; if it cannot be expelled in a timely manner, it creates high pressure inside the product, leading to crack formation. Additionally, the uneven pore structure of under-burnt calcined coke can result in uneven thermal stress distribution during graphitization, further exacerbating crack formation.
- Impact: Cracks reduce the mechanical strength and electrical conductivity of the product and may even cause it to fracture during subsequent processing or use.
Uneven Density:
- Formation Cause: The uneven pore structure of under-burnt calcined coke leads to inconsistent material migration and densification during graphitization. Some areas may experience insufficient densification due to excessive pores, while others may develop stress concentrations due to over-densification.
- Impact: Uneven density affects key performance indicators of the product, such as electrical conductivity, thermal conductivity, and mechanical strength.
Abnormal Volume Shrinkage:
- Formation Cause: Under-burnt calcined coke may undergo abnormal volume shrinkage during graphitization due to the decomposition of residual volatile substances or the reaction of impurities. This abnormal shrinkage can result in unstable product dimensions and even deformation.
- Impact: Abnormal volume shrinkage affects the dimensional accuracy and assembly performance of the product, reducing its overall quality.
Performance Degradation:
- Formation Cause: Due to the presence of the aforementioned defects, the graphitized products made from under-burnt calcined coke may exhibit lower electrical conductivity, thermal conductivity, and mechanical strength compared to those made from properly calcined coke.
- Impact: Performance degradation limits the application scope and service life of the product, reducing its market competitiveness.
Post time: Apr-28-2026