Basic facts about silica

Of all the oxide minerals in the Earth’s crust, silicon dioxide, or silica, is the most abundant.It is present in not only in combination with other oxide minerals but also in its isolated forms such as sand. The semi-precious mineral opal is a form of amorphous silica that has been prized for centuries.

Besides being the most abundant mineral on the Earth, it is also very important to life on our planet. Diatoms, a type of phytoplankton forming the base of the ocean’s food chain, have skeletons composed of silica.  Many plants use silica to stiffen stems for holding fruit and to form external needles for protection. The role of silica is less obvious in animals, but each one of us contains about half a gram of silica – without which our bones, hair, and teeth could not be formed.

Not only does silica play an important role in biology, it had played an important role in civilization. Flint is a form of silica that was used in ancient tools.The sand used in pottery is also a form of silica. Two-thousand year-old Roman cement contains amorphous silica from volcanic ash which helps give it high strength and durability. Present technology would be very different without the silica used to create the catalysts of our oil refineries, bind the molds for casting super-alloys, form modern glass and ceramics, and polish electronic materials.

What exactly is silica?

Silica is another name for silicon oxides - the most prevalent type being SiO2. It can be found in nature in crystalline form (as quartz sand), and it is the most abundant component of the earth's crust. Amorphous silica, on the other hand, is industrially manufactured in a variety of forms - including silica gels, precipitated silica, fumed silica, and colloidal silica.

What does "colloidal" mean?

A colloid is a stable dispersion of particles - particles that are small enough that gravity doesn't cause them to settle, but large enough not to pass through a membrane and allow other molecules and ions to pass freely. Particle sizes range from about 1 to 100 nm.

How does colloidal silica differ from fumed, fused, or precipitated silica?

Colloidal silica varies from other types of silica in several significant ways. The most noticeable difference is that it's in liquid form, as opposed to powder. In addition, it has the widest ranging surface area, and its aggregate size can be as small as the actual size of the primary particle.

What's the difference between sodium silicate (water glass) and colloidal silica?

Colloidal silica consists of dense, amorphous particles of SiO2.The building blocks of these particles are randomly-distributed [SiO4]-tetrahedra. This random distribution is what makes amorphous silica different from crystalline silica - ordered on a molecular level.  Sodium silicates are alkaline solutions with pH ranges of 12-13, compared to 9-11 for colloidal silica. Sodium silicates are also composed of silicate monomers, as opposed to colloidal silica composed of polymeric silicates.The composition of sodium silicates have a SiO2/Na2O ratio of approximately 3.4, whereas colloidal silica generally has a SiO2/Na2O ratio greater than 50. Finally, the viscosity of sodium silicates is much higher - closer to that of a syrup, while colloidal silicas have viscosities close to that of water.

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