The impurities in carbon black mainly include particulate impurities, water, solvent extracts and inorganic salts. Although these substances are in a small amount in carbon black, they have an impact on the quality and application of carbon black products. Therefore, production must be strictly in accordance with the standards. In some application fields, in order to achieve better results, the requirements for some related indicators of carbon black are more stringent. For example, the carbon black used in high-end coatings has lower requirements for impurities.
1. Particle impurities
The particulate impurities in carbon black mainly include hard carbon, iron filings and some other substances mixed in the packaging. The content and particle size of carbon black impurities have adverse effects on the performance of the product, and normal carbon black products are not allowed to have excessively large particles.
2. Solvent extract
Solvent extracts are hydrocarbons that remain on the surface of carbon black during carbon black production and are not completely cracked. The residual amount of these substances can be extracted with organic solvents such as benzene, toluene, and acetone, and measured. The small amount of solvent extractables has no effect on carbon black applications.
3. Moisture
The moisture in carbon black mainly comes from the moisture in the flue gas during production and the moisture in the air during post-production packaging, transportation and storage. The normal water content of carbon black has no adverse effect on the application, but if the water content is too high, it may cause processing difficulties, such as air bubbles in rubber processing, affecting appearance and other properties.
4. Ash content
Carbon burns completely in air with sufficient oxygen, and the residue is ash composed of inorganic salts. The ash in carbon black mainly comes from inorganic impurities and dissolved inorganic salts in raw oil and process water. Generally, the ash content is lower than 0.5%, which will not affect the application of carbon black. Some special applications may require lower ash content, such as conductive carbon black in cable materials. If the ash content exceeds a certain value, accidents such as discharge may damage the product.