Do you know several forms of silica
As we all know, the content of silicon in the earth's crust is about 26%, second only to oxygen. The existing form of silicon element in nature is mainly silicon dioxide. Silicon dioxide in the earth's crust mainly exists in silicon dioxide crystals. Although the molecular formula of silicon dioxide is SiO2, there is no single molecule of silicon dioxide in silicon dioxide crystals, but countless silicon atoms and oxygen atoms are connected with each other by silicon oxygen bonds to form a three-dimensional structure. Quartz, crystal, agate and other well-known minerals are silica crystals.
Because the silica crystal structure is stable, a large amount of silica crystal powder will be produced in the process of mining. If inhaled by the human body, these powders will deposit in the lungs and cannot be discharged. Over time, they will form what we usually call "silicosis" or "silicosis". However, the silica produced by our company belongs to synthetic nano silica, which does not have crystal structure. Macroscopically speaking, it is an aggregate of nano silica molecules, which is soluble in water and can be inhaled by the human body and eliminated with the blood circulation. It will not lead to silicosis due to deposition. Although fumed silica is amorphous silica, non-toxic and harmless, it is a kind of powder after all. If the concentration in the air is too high, it will also cause some discomfort in the human respiratory tract. Therefore, corresponding protective measures should be taken during production and operation.
The synthesis of nano-sized fumed silica is mainly prepared by chemical reaction. At present, there are two kinds of precipitation methods and gas phase methods. There are sol-gel methods in the laboratory. Only two methods of precipitation and gas phase preparation are discussed here. The synthesis method of nano silica by precipitation method is mainly the silica aggregate formed by the reaction of water glass (sodium silicate) solution with sulfuric acid and hydrochloric acid at a certain pH. Fumed silica is mainly amorphous nano silica prepared by high-temperature hydrolysis of silicon chloride in oxyhydrogen flame. The nano silica produced by the two methods has a very obvious difference.
From the appearance, because the water content of fumed silica is much lower than that of precipitated silica, the fluidity of fumed silica is better and it is easier to raise dust. The compaction density is generally only 1 / 4 of that of precipitated silica, and there is also a certain difference in the feel between the two. From the perspective of physical and chemical parameters, the pH of fumed silica is acidic because the silicon hydroxyl group on the surface is ionized in the solution, while the precipitated silica is generally neutral because of its preparation process and a large number of surface hydroxyl groups; The purity of fumed silica can reach more than 99%, while the purity of precipitated silica is generally between 90% - 95%; Fumed silica is generally nanometer, while precipitated silica is generally micron (nanometer).
In terms of price, the precipitation method has a longer development history, mature process, low cost and high output, so the price is low. While the gas-phase silica started late, with high equipment requirements, high cost investment and low output, so the price is higher than that of gas-phase silica. In terms of application fields, precipitated silica is mainly used as reinforcing agent and filler of rubber and plastics, and is widely used in tire, shoemaking, toothpaste, coating and other fields. Due to its special structure, aerosilica is mainly used as rheological additives, matting agents and anti sedimentation agents of coatings and paints, as flow additives in powder coatings, reinforcing materials of plastics, etc.
As a new nano material, fumed silica has incomparable properties with ordinary silica. It is not only widely used in traditional fields, but also in many high-end fields and new fields. Fumed silica will make great contributions to industrial development in the future.
JINSHA PRECIPITATED SILICA MANUFACTURING CO.LTD.
Email.: jk@jksilica.com
Add.: Gaosha Industrial Zone, Shaxian, Fujian, China
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