Structure and health hazards of silica
Silicon dioxide (chemical formula: SiO2) is an acidic oxide, the corresponding hydrate is silicate (H2SiO3). It has been known since ancient times. Silica is most common in nature in quartz, as well as in a variety of organisms. In many parts of the world, silica is the main component of sand. Silica is one of the most complex and abundant families of materials, being both a variety of minerals and produced synthetically. Applications range from structural materials to microelectronics to ingredients used in the food industry.
structure
SiO2 crystal has a variety of crystal forms, its basic structural unit is tetrahedral, each Si around the combination of 4 O, Si in the center, O in the four top angles; The smallest ring has six silicon atoms and six oxygen atoms. Many of these tetrahedrons are connected by the O of the vertex Angle, each O is shared by two tetrahedrons, that is, each O is combined with two Si. In fact, SiO2 crystal is composed of Si and O in a ratio of 1:2 three-dimensional network structure crystal. Therefore, SiO2 is usually used to represent the composition of silica. SiO4 tetrahedrons are found not only in SiO2 crystals but also in all silicate ores and are the basic skeleton that makes up the colorful silicate world.
Chemical properties
Silica is an acidic oxide, and the corresponding highest value hydrate is silicic acid (H2SiO3). Silica is chemically inactive and does not react easily with water and most acids. Salts are usually formed only by reacting with basic oxides. Hydrofluoric acid (HF) and concentrated hot phosphoric acid (H3PO4) are the acids with which you can react.
The chemical equation of its reaction with hydrofluoric acid to produce silicon fluoride is as follows:
SiO2 + 4 hf - SiF4 + 2 h2o
Salts are usually formed only by reacting with basic oxides. Such as:
SiO2 + CaO - CaSiO3
Reacts with a strong base to form a salt. Such as:
SiO2 + 2 and naoh Na2SiO3 + H2O
If there is a certain concentration of silica particles in the air, it will enter the lungs through human breathing, causing respiratory diseases, such as pneumoconiosis.
use :
Silicon dioxide is used in the food industry as an anticoagulant and is one of the Food Additives. Colloidal, precipitated or pyrolytic vapor silica is a common additive in food production. It is mainly used as a flowing agent or anti-caking agent in powdered foods such as spices and non-dairy coffee creamers, or as a powder in tablet form. It can absorb water in hygroscopic applications. Colloidal silica is used as a clarifier in wine, beer and fruit juices, E E551.
Health hazard
Silica ingested orally is essentially non-toxic with an LD50 of 5000mg/kg and is therefore perfectly acceptable for food use. However, inhaling fine dispersed crystallised silica dust can lead to silicosis, bronchitis or cancer because the dust stays in the lungs and continues to irritate tissues, thereby reducing lung volume. The study showed that workers exposed to crystalline silica had a 10 times higher rate of lupus and other autoimmune diseases than would be expected in the general population. Before new regulations were issued in 2013, the Occupational Safety and Health Administration (OSHA) allowed 100μg of silica per cubic meter of air, but the new rules reduce that to 50μg/m3. The exposure limit for the construction industry is also set to be reduced from 250 µg/m3 to 50 µg/m3.
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