Precipitated white carbon black and fumed white carbon black
Although white carbon black is called white carbon black, it has nothing to do with carbon. Just because it has a reinforcing performance similar to carbon black in rubber, and it is white, it is called white carbon black. The preparation method is to chemically extract the obtained silica powder, and its chemical composition is "hydrated silica".

There are two main methods for preparing white carbon black. One is the precipitation method. The process route is basically: first use fuel or gas at high temperature to react quartz sand with soda ash to prepare industrial water glass, and industrial water glass is prepared with water. Make a dilute solution of a certain concentration, then add a certain acid under certain conditions to precipitate the silica, and then wash, filter, dry, pulverize, and make the product white carbon black. The precipitation method is divided into acid method, sol method, carbonization method and many other specific methods. Our country mainly adopts acid method. The acid method is to react the soluble silicate with sulfuric acid (or other acid) together. When the reaction liquid reaches a certain pH value, the acid reaction is stopped, the aging is carried out, and then it is filtered and repeatedly washed with water. After removing the Na2SO4, After drying and crushing, the product is obtained.

The other is gas phase method, chemical vapor deposition (CAV) method, also known as pyrolysis method, dry method or combustion method. The raw materials are generally silicon tetrachloride, oxygen (or air) and hydrogen, which are formed by the reaction at high temperature. The reaction formula is: SiCl4+2H2+O2—>SiO2+4HCl. The air and hydrogen are respectively pressurized, separated, cooled and dehydrated, silica gel dried, dust removed and filtered, and then sent to the synthesis hydrolysis furnace. After the silicon tetrachloride raw material is sent to the rectification tower for rectification, it is heated and evaporated in the evaporator, and the dried and filtered air is used as the carrier to send to the synthesis hydrolysis furnace. After silicon tetrachloride is gasified at high temperature (flame temperature 1000~1800℃), it undergoes gas phase hydrolysis with a certain amount of hydrogen and oxygen (or air) at a high temperature of about 1800℃; the gas phase method white carbon black produced at this time The particles are extremely fine and form aerosols with gas, which are not easy to capture, so they are first aggregated into larger particles in the agglomerator, and then collected by the cyclone separator, and then sent to the deacidification furnace, and the gas-phase dioxide is purged with nitrogen-containing air The silicon is finished when the PH value is 4～6.

So, what is the difference between precipitation method white carbon black and gas phase method white carbon black?

The main difference between precipitation method white carbon black and gas phase method white carbon black lies in: particle size and purity.

Precipitated silica is generally micron-sized, and fumed silica is generally nano-sized. Precipitation method silica has high impurity content, and the purity is generally about 93%, while fumed silica has a very low impurity content, and the purity can reach more than 99%. Due to the huge difference in particle size and purity, fumed silica is superior to precipitated silica in terms of thickening, thixotropy, anti-settling, reinforcement, matting, and friction. Let's take a look at the specific applications of hydrated silica with the editor.

Rubber reinforcement
Silica is widely used as a reinforcing agent in the rubber field, and its amount accounts for 70% of the total amount. Especially when manufacturing white, colored and light-colored rubber products, the white carbon black is more suitable for easy coloring. For example, the tensile strength of unreinforced silicone rubber does not exceed 0.4 MPa, and the strength can be increased by 40 times after being reinforced by gas phase silica.

Matting agent
White carbon black has a huge surface area with a refractive index of 1.45-1.50. The paint film containing hydrated silica matting agent will diffusely reflect when light enters, thereby forming a glossy matte and matte appearance. Fumed silica particles are looser, and the number of particles per unit mass is more than that of precipitated silica. Therefore, with the same addition amount, fumed silica has a higher matting effect and better transparency.

Friction
In addition to the large surface area, the adsorption capacity of hydrated silica is also very strong. Therefore, hydrated silica is one of the main types of toothpaste friction agents. Due to the superior transparency and friction of fumed silica, many are crystal clear Fumed silica is found in the ingredients of toothpaste.

Used for gluing and strengthening of paper
Hydrated silica has excellent abrasion resistance and strength. As mentioned above, it is very "white". Therefore, when hydrated silica is used in paper, it can increase the whiteness and opacity of the paper and make the paper more wear-resistant. Oil resistance, better gloss. For example, adding 1-2% fumed silica to newsprint can reduce the weight of the paper by 10%, increase the strength, and prevent ink penetration.

Anti-sedimentation and flow aid effect
When used in adhesives and sealants, hydrated silica can control rheology, prevent sedimentation, prevent sagging and strengthen. In addition, fumed silica is widely used in paints, inks and coatings as rheology additives, anti-settling agents, and dispersants with superior performance.

Protection and transportation in cosmetics and medicines
When used in cosmetics, fumed silica can effectively reflect ultraviolet rays, has a matting effect, and does not decompose or change color after irradiation; when used as a carrier, it can also extend the efficacy of the drug and promote the absorption of drugs or skin care products, while the precipitation method Silica generally does not meet this requirement.