The chemical molecular formula of white carbon black is sio2nh2o. Because its use is similar to carbon black and it is white, it is named white carbon black. According to different production methods, white carbon black can be divided into precipitated white carbon black (precipitated hydrated silica) and fumed white carbon black (fumed silica). The production methods of the two products are different, and their properties and uses are also very different. The gas phase production mainly uses silicon tetrachloride and the silicon dioxide obtained by air combustion. The particles are fine, and the median particle size can be less than 5 microns. Precipitation method is to add sulfuric acid into sodium silicate to precipitate silicon dioxide. The median particle size is about 7-12 microns. Fumed silica is expensive and difficult to absorb moisture. It is often used as a matting agent in coatings. Precipitated silica is cheap and easy to absorb moisture. It is mainly used as filling and reinforcing agent in rubber and plastic products. The products described below are produced by sulfuric acid precipitation method, i.e. precipitation method white carbon black. The white carbon black involved below is precipitation method white carbon black.


White carbon black


1、 Production principle of precipitated silica

Sodium silicate reacts with sulfuric acid to produce hydrated silicic acid Na2O · msio2 ＋ H2SO4 ＋ nH2O － → Na2SO4 ＋ msio2 · (n ＋ 1) H2O ↓

(the reaction process needs to be heated). The reaction solution is pressure filtered, dewatered, washed, and pulped to obtain white carbon black slurry. The white carbon black product is obtained by spray drying.


2、 Main uses of precipitated silica

Since the industrial production in 1940s, white carbon black products have been widely used as reinforcing agent in rubber products. In addition, they can also be used in pharmaceutical industry, pesticide, ink, paint, coating, toothpaste, paper, food, feed, cosmetics, battery and other industries. Here is a brief introduction to the main application industries applicable to lime Black:


1. Tire industry

The use of white carbon black in tire tread compound, especially the combination of highly dispersive precipitated white carbon black and coupling agent, can simultaneously improve tire life (improve wear resistance) and safety (improve wet skid resistance), and reduce fuel consumption (reduce rolling resistance). In addition, precipitated silica used in tire carcass and belt layer can improve the adhesion between rubber compound and steel cord; Replacing carbon black with white carbon black in tire sidewall compound can greatly improve the durability, flex resistance and impact resistance of the compound.


2. Rubber shoes and other rubber products

(1) The white carbon has high black-and-white degree and fine particles. The vulcanizate made of white carbon has high transparency and can improve the comprehensive physical properties of the compound. Therefore, as the main reinforcing filler, silica is widely used in the production of rubber shoes, especially in transparent and translucent sole compounds.


(2) In the production of tape, in order to improve its wear resistance, a large amount of white carbon black is added. At the same time, the silane alcohol on the surface of white carbon black plays a role in improving the wetting degree of rubber and fabric, which is conducive to the diffusion and penetration of rubber. In addition to the above products, white carbon black is also used in rubber rolls, rubber hoses, rubber plates, wires and cables, as well as rubber parts in household appliances and stationery.

3. Silicone rubber

The application of silicone rubber began with the appearance of white carbon black. Silicone rubber has high heat resistance, excellent cold resistance, ozone resistance, aging resistance and atmospheric aging resistance, as well as excellent electrical insulation. Due to the above characteristics, silicone rubber is widely used in aerospace, electronic industry and other industries. The price of fumed silica is high. Precipitated silica, which is relatively cheap, can be used to replace fumed silica in the production of low-grade silicone rubber.


4. Pharmaceutical industry

White carbon black is physiologically inert, highly absorbent, dispersive and thickening, and has been widely used in pharmaceutical preparations. For example, white carbon black is widely used as a carrier in quasi biotin E powder.

5. Pesticide industry

The main function of white carbon black in the pesticide industry is to act as a carrier to improve fluidity and prevent caking. At present, white carbon black is mainly used in various wettable powders.

6. Application in ink

White carbon black mainly plays a thickening role in printing ink and is used to control the flow of printing ink. It is also used to control the ink flow of the printer, so that it cannot flow or hang freely, so as to obtain clear printing.

3、 Significance of various indexes of silica in application

1. The reinforcement effect of silica with specific surface area mainly depends on its specific surface area. Generally, with the increase of specific surface area, various strength indexes of rubber products increase, but the resilience decreases, the tear strength decreases, it is not wear-resistant, it is difficult to disperse during mixing, the heat generation is high, the Mooney viscosity of rubber is high, and it is easy to scorch. Therefore, the specific surface area is required to be different for different formulations and uses, The effect of specific surface area on the physical and mechanical properties of vulcanized rubber is not consistent.


2. Oil absorption value oil absorption value reflects the degree of structure. With large oil absorption value and small degree of structure, the tensile strength, tensile strength and hardness of vulcanizate are generally large, especially the wear resistance is small, but the elongation is low.


3. The loss on ignition at 900 ℃ reflects the surface hydroxyl group. When there are too many hydroxyl groups on the surface, it is easy to cause the structure of rubber composites and make the materials brittle. The processability is affected, the vulcanizate is easy to fall off, and the surface hydroxyl has a strong adsorption on the vulcanization accelerator, which prolongs the vulcanization time.

4. The heating reduction at 105 ℃ reflects the amount of free water in the particle gap. When the heating reduction is too small, the rubber is highly structured, and it becomes difficult to make rubber. If the heating reduction is zero, the white carbon black is useless, and it is generally appropriate to control it at about 6%.

5. The pH value is generally about 7. When the pH value increases (the acidity decreases), the vulcanization speed of the compound is accelerated.

6. The less the soluble salt content, the better. However, if you want to significantly reduce the soluble salt content, the production cost will be greatly increased.