Silicon compounds are the most abundant component of the Earth's crust. Sand is the primary source of silicon due to its abundance, simplicity of mining, and processing. Quartzite, a metamorphic rock, is another potential source. Silicon (Si) is classified as semi-metallic or metalloid since it has certain metallic qualities. Silica gel was first discovered in the 1640s as a scientific curiosity. During World War I, it was used to absorb vapors and gases from gas mask canisters. Walter A. Patrick, a chemistry professor at Johns Hopkins University, patented the synthetic silica gel manufacturing process in 1918.

Silica may be referred to as silica sand or quartz sand. It consists of Silicon dioxide is also known as silica. It occurs naturally in abundance as sand and serves as a raw material for several valuable compounds, including silicone and silicates. It can also be found as a byproduct of several chemical plants. Silicon is never found naturally; rather, it exists as the silicate ion SiO44- in silica-rich rocks such as obsidian, granite, diorite, and sandstone. Feldspar and quartz are the most important silicate minerals. Silicon alloys contain a variety of metals such as iron, aluminum, copper, nickel, manganese, and ferrochromium. Silica (SiO2) has remarkable qualities due to the ability of its elemental bricks, SiO4 tetrahedra, to be joined together to form a wide range of amorphous crystalline solids that can be microporous, mesoporous, or macroporous. Silica that has been polished and created to provide specialized functionality is known as synthetic amorphous silica (SAS). SAS is classified into four types: colloidal, fumed, precipitated, and silica gel.

Colloidal silica:

Colloidal silica particles are incredibly tiny, measuring between a few nanometers to tens of nanometers. As a result, colloidal silica particles have extremely large surface areas, making them highly reactive through silanol groups on the particle surface. These silanol groups create ionic and hydrogen connections with polymer functional groups, metal ions, different surfaces, and even silica particles themselves. This makes colloidal silica a useful surface modification, crosslinker, binder, and reinforcing agent in a variety of industrial applications. 

  1. Increasing Concrete Densification: Colloidal silica’s small particles penetrate deep into concrete to react with calcium hydroxide to form calcium silicate hydrate, increasing concrete strength. 
  2. Creating and Enhancing Catalysts: In addition to being a highly pure raw material for catalysts, colloidal silica also improves attrition resistance, durability, and adhesion to substrates. 
  3. Enhancing Paint and Coating Resiliency: Colloidal silica forms strong ionic and hydrogen bonds with coating polymers and substrates to enhance adhesion and resistance to abrasion and blocking. 
  4. Strengthening Refractories: Ceramic fibers used in refractories are bonded and treated with colloidal silica to increase resistance to thermal shock and chemical exposure.
  5. Frictionizing Paper Surfaces: Colloidal silica increases the coefficient of friction on paper and paperboard surfaces to reduce slipping and skidding.

Fumed silica:

Fumed silica is a light, fluffy powder made of amorphous silica particles produced by agglomerating chain-like silica aggregates and primary particles in a flame hydrolysis process. The fumed silica particles are extremely small, usually on the order of tens of nanometers. However, they feature a large surface area and high reactivity. Fumed silica particles may be surface modified to impart hydrophobicity or introduce functional groups. When incorporated into formulations, these particles must be properly mixed, and care must be taken to prevent the risk of inhalation.

  1. Improving Food and Beverage Consistency: The high binding capacity of fumed silica helps prevent caking in food products and thickens beverage products.

  2. Paint and Coating Rheology Modification: Fumed silica controls rheology and imparts anti-settling and anti-sagging properties when added to paints and coatings.

  3. Enhancing Flow in Tablet Production: Fumed silica improves the flow properties of powders used in pharmaceutical tablet production, preventing inconsistency and improving quality.

  4. Controlling Cosmetic Appearance: Adding fumed silica to cosmetics can enhance their look by creating a smoother and matte appearance.

Precipitated silica:

Precipitated silica is a solid product made up of amorphous silica particles that form during a silicate salt precipitation reaction. The particle size of precipitated silica is substantially greater than that of fumed silica, which is on the scale of tens of nanometers. The greater size of these particles allows for the use of amorphous silica's porosity to develop adsorptive characteristics. Manufacturers regulate the particle size and porosity of precipitated silica to create distinct grades that are better suited to specific applications. Precipitated silica must be thoroughly blended into liquid formulations to form a suspension.

  1. Boosting Oral Care Cleaning: Precipitated silica provides polishing and cleaning and induces thickening in oral care products, such as toothpaste.

  2. Enhancing Food and Pharmaceutical Consistency: Adding precipitated silica prevents caking and clumping in powdered food products and pharmaceutical formulations.

  3. Providing Material Reinforcement: Incorporation of precipitated silica into materials such as rubber can provide reinforcement and strengthening.

  4. Modifying Film Appearance: Precipitated silica reduces gloss and provides a matte effect to coatings, paints, and inks.