Silicas Technology

Synthetic silica can be in two major groups by different production process. That's fumed silica and preciptated silica.....

Fumed silica and Precipitated silica

Fumed silica and Precipitated silica

Both of fumed silica and precipitated silica are silicas, or silica dioxide(SiO2). Their cost different is mainly due to different production technology and raw materials.

Fumed silica and precipitated silica are for different applications. As a result of their different properties, both are easily found in various industries and medical area.

Difference in their contents are as follows.
Particle size: precipitated silica is usually in µm(micron meter). while fumed silica is in nm(nano meter).
Impurity: precipitated silica assay around 93%, with higher impurity. While fumed silica assay above 99%, with very low impurity.

Difference in the applications are also different.
Fumed silica is mainly used as a reinforcing agent for silicone rubber, coatings and unsaturated resin thickener, ultrafine silica gels and aerogels used primarily as paint matting agents, thickeners, plastic film opening agent.
Precipitated silica is mainly used as a natural rubber and synthetic rubber reinforcing agent, friction  agent in toothpaste.

More details of the two are quoted from Wikipedia as follows.
Precipitated silica
Precipitated silica is a silica (SiO2) produced by precipitation from a solution containing silicate salts. In 1999, more than 1M tons/y were produced, mainly for use in tires and shoe soles.
The production of precipitated silica starts with the reaction of an alkaline silicate solution with a mineral acid. Sulfuric acid and sodium silicate solutions are added simultaneously with agitation to water. Precipitation is carried out under alkaline conditions. The choice of agitation, duration of precipitation, the addition rate of reactants, their temperature and concentration, and pH can vary the properties of the silica. The formation of a gel stage is avoided by stirring at elevated temperatures. The resulting white precipitate is filtered, washed and dried in the manufacturing process.[2]
Na2(SiO2)7 + H2SO4 → 3.3 SiO2 + Na2SO4 + H2O
The particles are porous. Primary particles with a diameter of 5 - 100 nm, and specific surface area 5-100 m2/g. Agglomerate size is 1 - 40 µm with average pore size is > 30 nm. Density: 1,9 - 2,1 g/cm3.
Filler, softener and performance improvement in rubber and plastics
Cleaning, thickening and polishing agent in toothpastes for oral health care
Food processing and pharmaceuticals additive as anti caking, thickening agent, absorbent to make liquids into powders.
Food rheology modifier
Defoamer component.
Fumed silica
Fumed silica, also known as pyrogenic silica because it is produced in a flame, consists of microscopic droplets of amorphous silica fused into branched, chainlike, three-dimensional secondary particles which then agglomerate into tertiary particles. The resulting powder has an extremely low bulk density and high surface area. Its three-dimensional structure results in viscosity-increasing, thixotropic behavior when used as a thickener or reinforcing filler.
Fumed silica has a very strong thickening effect. Primary particle size is 5–50 nm. The particles are non-porous and have a surface area of 50–600 m2/g. Density 160–190 kg/m3.
Fumed silica is made from flame pyrolysis of silicon tetrachloride or from quartz sand vaporized in a 3000 °C electric arc. Major global producers are Evonik (who sells it under the name Aerosil®), Cabot Corporation (Cab-O-Sil®), Wacker Chemie (HDK®), Dow Corning, and OCI (Konasil®).
Fumed silica serves as a universal thickening agent and an anticaking agent (free-flow agent) in powders. Like silica gel, it serves as a desiccant. It is used in cosmetics for its light-diffusing properties. It is used as a light abrasive, in products like toothpaste. Other uses include filler in silicone elastomer and viscosity adjustment in paints, coatings, printing inks, adhesives and unsaturated polyester resins. It is also used in the production of cat box filler.

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