Comparison between silica and carbon black, the difference between precipitation silica and vapor phase silica

　　Comparison between white carbon black and carbon black

　　①The obvious difference is the color. White carbon black is white and can be used to make various colored products and transparent products; while carbon black can only be used to make gray and black products.

　　② Compared with carbon black, white carbon black has a higher surface area and finer particles. A large surface area means high activity. The tensile strength, tear strength and wear resistance of vulcanized rubber are high, but the elasticity is reduced. Therefore, the viscosity of the mixed rubber increases and the processing performance decreases. The surface of white carbon black has more micropores than carbon black, so the increase in the surface area of white carbon black does not improve the rubber reinforcement as much as that of carbon black. The structure of silica black is also higher than that of carbon black. This is because the hydrogen bonding on the surface of silica black makes the agglomerates formed more and stronger than carbon black. Therefore, the viscosity of silica black rubber with high surface area and high structure is Very high, which is detrimental to processing. Precipitation silica has silanol groups on its surface; gas phase silica also has silanol groups on its surface. The pH value of precipitation silica is either acidic or alkaline: vapor phase silica is acidic.

　　③The surface of white carbon black is highly hydrophilic (carbon black is hydrophobic). In particular, the surface of precipitation silica is more microporous and more hygroscopic. The hydrophilicity of silica is not conducive to reinforcement. High moisture content will cause scorching. On the other hand, the activity of a large number of -OH groups on the surface of white carbon black will have a strong adsorption effect on the vulcanization system in the rubber compound and delay vulcanization. Therefore, it is important to modify silica (from hydrophilic to hydrophobic) and prevent moisture.

　　What is the difference between precipitation silica and vapor phase silica?

　　(1) Difference in manufacturing methods: There is essentially no difference between silica produced by the gas phase method and silica produced by the precipitation method. The chemical names are both silica. However, the gas phase production method uses silica obtained by burning silicon tetrachloride and air, with a fineness of more than 1,000 mesh. The precipitation method production uses sodium silicate, adding sulfuric acid or hydrochloric acid to precipitate the silica. The fineness of conventional precipitated silica is only 300~400 days.

　　(2) Difference in basic physical parameters: Precipitation silica contains crystal water, so it is also called hydrated silica (SiO2·nH2O). Silica, content 87%~95%, average particle size 11~100nm, density 1.93 ~2.05g/cm3, pH value 5.7~9.5. Vapor-phase white carbon black is also called anhydrous silica (SiO2), with a silica content of more than 99.8%, an average particle size of 8~19nm, a density of 200g cm, and a pH value of 3.9 ~4.0. The reinforcing properties of silica mainly depend on surface area (or particle size), structure and surface chemical properties. The surface area is measured by BET method or CTAB method, and the structure is measured by DBP value or DOP value.

　　(3) Performance difference

　　① Vapor phase silica

　　Advantages: good reinforcement, high tensile strength and tear strength, good wear resistance, faster hardening than precipitation silica, and good transparency.

　　Disadvantages: Compared with precipitation silica, it is easier to fly, generates serious heat, is expensive, and has poor processability (slow powder consumption and poor fluidity).

　　②Precipitation silica

　　Advantages: cheaper than gas-phase silica, better processability than gas-phase silica, not as serious as gas-phase silica, compression permanent deformation slightly better than gas-phase silica, heat generation better than gas-phase silica Black is slightly lower.

　　Disadvantages: The reinforcing property is worse than that of gas phase silica, and the transparency is poor.