Precipitated Silica: Properties, Production Process and Applications

Precipitated Silica

Precipitated silica, also known as synthetic amorphous silica, is a form of silicon dioxide manufactured by chemical reactors. Unlike other types of silica, it is produced synthetically rather than being produced naturally. Synthetic amorphous silica is most commonly produced through a chemical reaction involving sodium silicate and sulfuric acid. This reaction results in the formation of ultrafine silicon dioxide particles that agglomerate strongly to form a stable network of silica bodies.

Production Process of Precipitated Silica

The production of synthetic amorphous silica begins with the dissolving of quartz pebbles or sand in an alkaline solution. This forms waterglass or sodium silicate which is then used to manufacture synthetic amorphous silica. In the reactors, sulfuric acid is added to waterglass under controlled conditions to precipitate silica particles. The precipitate is then filtered, washed and dried to yield the final synthetic amorphous silica powder.

The key steps involved in the production of synthetic amorphous silica are:

- Dissolving: Quartz is dissolved in an alkaline solution forming waterglass or sodium silicate. This reaction is called the waterglass process.

- Reaction: Sulfuric acid is added into the reactor containing waterglass under agitation. This promotes the precipitation of amorphous silica particles.

- Filtration: The precipitate formed is separated from the liquor through a multi-stage vacuum filtration process to remove impurities.

- Washing: The cake is washed thoroughly with water to remove residual impurities like sodium and sulfate ions.

- Drying: The washed filter cake is then dried using hot air or a spray dryer to yield the final synthetic amorphous silica powder.

- Classification: The powder is milled and classified to obtain the desired particle size distribution for different applications.

Physicochemical Properties of Precipitated Silica

Synthetic Precipitated Silica has some distinct physicochemical properties that make it useful for various applications:

- Amorphous Structure: It has an amorphous structure lacking long-range order, unlike crystalline silica. This provides better reinforcement and viscosity improvement.

- High Purity: The production process allows achieving over 99% purity levels with very low metallic impurities.

- Large Surface Area: The nanoscale particles have a very large specific surface area ranging from 100-400 m2/g. This enhances physical properties.

- Low Bulk Density: The fluffy, porous structure gives it a low bulk density of 30-40 kg/m3.

- Oil Absorption: The porous structure allows absorbing oils and organic materials 5-10 times its own weight.

- Reinforcing Ability: It can reinforce elastomers and plastics by forming a stabilizing network structure during blending.

- pH Stabilization: Precipitated silica acts as a pH buffer, stabilizing products against fluctuations in pH.

Applications of Synthetic Amorphous silica

Given its unique properties, synthetic amorphous silica finds wide usage in various industries:

Rubber Industry

Precipitated silica is a key reinforcing filler and processing aid for the rubber industry. It is used in the production of tires, mechanical rubber goods, hoses and belts to enhance properties like abrasion resistance and stiffness.

Oral Care

It is used as a thickening agent and abrasive in toothpastes, mouthwashes and dental impression materials due to its thickening, suspending and polishing capabilities.

Food Industry

Synthetic amorphous silica is approved as a food additive called E551. It is used as an anti-caking agent in powders like sugar and seasoning blends and as a flow agent in powders and granules.

Pharmaceuticals

It acts as a glidant and release retardant in tablets and also enhances the flowability of powders. Precipitated silica prevents the formation of lumps.

Cosmetics

It has wide applications in cosmetic formulations like creams, lotions, powders and hair care products where it acts as a thickening agent, absorber or carrier for active ingredients.

Other industries

Precipitated silica also finds niche applications in areas like coating, oil well cement, ceramic, castable refractories, semiconductors etc. due to its dispersion, thixotropic and reinforcing properties.

Synthetic amorphous silica is a synthetically produced amorphous silica with a unique combination of high purity, large surface area, good reinforcing ability, and oil absorption capacity. These properties make it highly useful across industries like rubber, oral care, foods, pharmaceuticals, cosmetics and more. The distinct production process via acid precipitation allows tailoring synthetic amorphous silica 's characteristics as per various application needs. With its excellent functionality and wide industrial compatibility, precipitated silica is expected to witness increased demand and usage going forward.

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