Classification of Silica
Silica is a general name for finely powdered or ultrafine particles of anhydrous and hydrous silica or silicates. It is a white, non-toxic, amorphous fine powder with a large SiO2 content (greater than 90). %) Currently, the common silica on the market is fumed silica and precipitated silica.


1. Precipitated Silica


Precipitated silica (scientific name precipitated hydrated silica) is mainly used in footwear, tires and other light-colored rubber products. Other uses include use as a carrier or flow agent in pesticides, feeds, etc., used in toothpaste. A friction agent used as a dispersant, anti-precipitant or matting agent in coatings.


The precipitation method is also known as the wet method, and the main raw materials are quartz sand, soda ash, industrial hydrochloric acid, sulfuric acid, nitric acid or carbon dioxide. The production process mainly includes steps of precipitation, filtration, drying and granulation. Industrial water glass is prepared by reacting quartz sand with soda ash at high temperature by using fuel oil or high quality coal; industrial water glass is formulated into a dilute solution of a certain concentration with water, and then an acid is added under certain conditions to form hydrated silica precipitate. According to the requirements of the finished product, it is filtered and washed in a roller filter press or a plate filter press to remove excess water and reaction by-products to obtain a white carbon black filter cake; and then dried (usually spray-dried) to obtain a finished product. If further grinding or granulation is carried out, a range of products can be obtained.


2. Fumed Silica

Fumes Silica (scientific name fumed silica) is a multifunctional additive used in the field of rubber for room temperature vulcanized silicone rubber (RTV), heat vulcanized silicone rubber (HTV), etc. Other uses include coatings, Adhesives, inks, chemical mechanical polishing, paper, food and gel batteries, etc., can play the role of thickening, thixotropic, extinction and anti-settling.


The production method of fumed silica is mainly a chemical vapor deposition (CAV) method. This process is also known as pyrolysis, dry or combustion. The preparation process is that the silicon tetrachloride (or methyltrichlorosilane) raw material is sent to the rectification column for rectification, heated and evaporated in an evaporator, and sent to the synthetic hydrolysis furnace by using the dried and filtered air as a carrier. . The advantage of the gas phase method is that the production process is relatively simple, and the reaction conditions are easy to control. The purity of the product can be as high as 99.8%, the specific surface area is large, the activity is high, and the surface hydroxyl group is small, which is suitable for the synthesis of high-purity white carbon black; The adsorption water and the preparation process lead to acid regions on the surface, making the carbon black hydrophilic, difficult to infiltrate and disperse in the organic phase, high production cost, high product price, small application range and low yield. The specific operation control of the production process of fumed silica is difficult, especially for the production of high-grade products (high specific surface area products). The technical difficulties are three aspects of heat dissipation of the synthesis furnace, high-efficiency separator operation control and hydrogen chloride desorption. The most difficult to control is the gas phase equilibrium and gas-solid phase equilibrium of the system. In terms of surface modification, multinational companies adopt continuous dry surface modification processes, and they all develop in the direction of high efficiency, energy saving and environmental protection. Domestic research in this area is still in a backward state.