Name:Silicon dioxide
Synonyms:Quartz
Molecular Formula:SiO2
Molecular Weight:60.08
CAS Registry Number:14808-60-7
EINECS:238-878-4
The chemical compound silicon dioxide, also known as silica (from the Latin silex), is an oxide of
silicon with a chemical formula of SiO2 and has been known for its
hardness since antiquity. Silica is most commonly found in nature
as sand or quartz, as well as in the cell walls of diatoms. It is a
principal component of most types of glass and substances such as
concrete. Silica is the most abundant mineral in the earths
crust.SiO2 has a number of distinct crystalline forms in addition to
amorphous forms. With the exception of stishovite and fibrous
silica, all of the crystalline forms involve tetrahedral SiO4 units linked together by shared vertices in different
arrangements.
Applications
It is used in the production of various products.
Inexpensive soda-lime glass is the most common and typically found
in drinking glasses, bottles, and windows.
A raw material for many whiteware ceramics such as earthenware,
stoneware and porcelain.
A raw material for the production of Portland cement.
A food additive, primarily as a flow agent in powdered foods, or to
absorb water (see the ingredients list for).
An oxide layer grown on silicon is hugely beneficial in
microelectronics. It is a superior electric insulator, with high
chemical stability. In electrical applications, it can protect the
silicon, store charge, block current, and even act as a controlled
pathway to allow small currents to flow through a device. The
traditional method of manufacture such an oxide layer has been to
heat the silicon in a high-temperature furnaces within an oxygen
ambient (thermal oxidation).
As hydrophobic silica it is used as a defoamer component.
As hydrated silica in toothpaste (abrasive to remove plaque.)
As a high-temperature thermal protection fabric.
In cosmetics for its light-diffusing properties and its absorbency.
Liquid silicon dioxide (colloidal silica) is used as a wine and juice fining agent.
As a glidant in pharmaceutical products silicon dioxide aids powder
flow when tablets are formed.
Inhalation health effects
Inhaling finely divided crystalline silica dust or fumed silica in
very small quantities (OSHA allows 0.1 mg/m3) over time can lead to
silicosis, bronchitis or (much more rarely) cancer, as the dust
becomes lodged in the lungs and continuously irritates them,
reducing lung capacities (silica does not dissolve over time).
This effect can be an occupational hazard for people working with
sandblasting equipment, products that contain powdered crystalline
silica and so on. Children, asthmatics of any age, allergy
sufferers and the elderly (all of whom have reduced lung capacity)
can be affected in much shorter periods of time.
| Item | Specification | Result |
| Appearance | White powder | White powder |
| Purity of SiO2 (after ignition) | 95% Min. | 98.5% |
| Whiteness | 93% min. | 98% |
| Residue on 320 mesh screen | 98% Min. | 99% |
| Water absorption value | / | 54 mL/20g |
| Refractive index | 1.435-1.46 | 1.45 |
| pH (5% suspension) | 6.5-8.5 | 6.9 |
| Loss on drying (at 105) | 10% Max. | 5.7% |
| Residue on ignition | 8.3% Max. | 4.4% |
| Iron assay | 1000 ppm max. | 170 ppm |
| Sulphate content | Negative | Negative |
| Soluble dissociated salt (Sodium sulfate) | 0.4% Max. | 0.4%Max |
| Heavy metal (as Pb) | 20 ppm Max. | 20 ppmMax |
| Arsenic (As) | 2 ppm Max. | 2 ppmMax |
| Total plate count | 200 cfu/g Max. | 45 cfu/g |
Packing: 8kg/bag or 10kg/bag
Storage: stored in a dry and cool place, keep away from light and
heat and any acid substance.
Shelf life: two years when stored properly.
