Silicon Dioxide

What is SiO2?

Silicon Dioxide is a natural compound of oxygen and silicon, found mostly in the sand.

It is also known as Silica, composed of silicon and oxygen, having chemical formula SiO2, or silicon dioxide. There are various forms of Silica, and all silica forms are identical in chemical composition but contain different atom arrangements. 

Silica has three primary crystalline varieties, quartz, tridymite, and cristobalite. Silica dust from fine particulate quartz rock causes over a long-term progressive lung injury, silicosis. (NCI04). The SiO2 chemical name is Silicon Dioxide.

Silica compounds are further divided into amorphous Silica (a-silica or non-crystalline Silica) and crystalline (or c-silica).

c-Silica compounds have structures with repeating patterns of both silicon and oxygen. 

a-Silica chemical structures are more randomly linked to that of c-silica.

All silica forms are odorless solids composed of silicon and oxygen atoms obtained as transparent to grey in its crystalline or amorphous powdered form. Silica particles get suspended in air and form non-explosive dust. Silica can be combined with oxides and other metallic elements for the formation of silicates.

SiO2 Structure

Silicon dioxide is otherwise called silicon (IV) oxide.

There exist three different silicon dioxide crystal forms. The easiest one to draw and remember depends on the diamond structure.

The crystalline silicon has a similar structure as diamond. To turn it into silicon dioxide, all we are supposed to do is modify the silicon structure by adding some oxygen atoms.

The simple SiO2 structure is represented in the following way.

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If we notice properly, each silicon atom is bridged to its neighbour ones by an oxygen atom. Remember that this is just a tiny part of a giant SiO2 structure that extends on all three dimensions.

Silicon Dioxide Properties

The basic SiO2 properties of both physical and chemical are given below.

Physical Properties of SiO2

Silicon dioxide is transparent to gray, crystalline, odorless, or an amorphous solid. They have melting and boiling points as 1713º C and 2950º C, respectively. The density is about 2.648 g/cm3. It is insoluble in both acid and water and soluble in hydrofluoric acid. Its molecular weight is about 60.08 g/mol.

Chemical Properties of SiO2

Silicon dioxide is not a very reactive compound because the polarity of the molecule is zero. The ‘Si’ forms two double bonds with the oxygen. Therefore, it’s a very stable molecule. Moreover, it has high dielectric strength, so that it is used as an insulator and semiconductor.

Production of Silicon Dioxide

The acidification sodium silicate solutions obtain precipitated Silica or amorphous Silica. Its gel is washed and dehydrated to make colourless microporous Silica. The reaction involving a trisilicate along with sulfuric acid is provided below.

Na2Si3O7 + H2SO4 → 3SiO2 + Na2SO4 + H2O

Silicon Dioxide Reactions

Silica converted into silicon by reducing carbon.

When fluorine reacts with silicon dioxide, it produces O2 and SiF4.

Silicon dioxide also reacts with hydrofluoric acid to form hexafluorosilicic acid (H2SiF6).

SiO2 + 6HF →  H2SiF6 + 2H2O

Preparation of Silicon Dioxide

Most of the silicon dioxide is extracted even from quartz mining, it can also be prepared using acid neutralization of an aqueous alkali metal - silicate solution. This kind of method is known as a wet process and forms amorphous SiO2 particles.

Na2Si3O7 + H2SO4 --> 3 SiO2 + Na2SO4 + H2O

The other methods form pyrogenic Silica, having silanes combustion like silicon tetrachloride, in an oxygen-hydrogen burner. These are the fine particle product aggregates of 100 - 400 nm in diameter.

SiCl4 + 2H2 + O2--> SiO2 + 4 HCl

Applications of Silicon Dioxide

Silica exists as fluffy, and white powders produced through a wet process, yielding a thermal route, Silica, or silica gel, yielding a pyrogenic (fumed) silica.

In powdered foods, the Silica clings to the food particles and prevents them from clumping. Doing this allows powdery products to remain free-flowing, and to separate other products easily.

Also, Silicon dioxide functions as a defoaming agent, conditioning agent, carrier, chill proofing agent in malt beverages like beer and filter aid.

Besides, it is used in material manufacture like paper and adhesives for food-packaging materials.

As per the U.S. FDA regulation’s direct additive, the SAS levels cannot exceed 2% by the food weight, and as an indirect additive, it can be used only in the required amount to produce the intended functional effect.

Silicon Dioxide Uses

There are various Silicon dioxide uses in electronic, chemical, and pharmaceutical industries. In the chemical industry, it is used in the production of adhesives and sealants, adsorbents, ceramic, porcelain, corrosion inhibitors, anti-adhesives, dyes, and paint additives. In addition, silicon dioxide production occurs in agricultural chemicals. Coming to pharmaceutical industries, it helps as an additive of food and medicines to absorb water. For telecommunication, SiO2 is the main component of optical fibers. Silicon dioxide is extensively used as a precursor to obtaining glass and silicon by the reaction given below.

SiO2 + 2C → Si + 2CO

Furthermore, Silicon dioxide is also used in the construction industry to produce concrete. Used in hydraulic fracturing in its crystalline form, and in glass production, as a Sedative, production to produce elemental silicon, as an anti-caking agent in powdered foods such as spices, as a fining agent in beer, juice, and wine, in pharmaceutical tablets, and in toothpaste to remove the tooth plaque.

Health Hazards

Orally Silica is non-toxic when ingested. According to a study report conducted in 2008, the higher the rates of Silica in water, the lower the likelihood of dementia. As a result, the dosage was raised to 10 mg/day of Silica in drinking water as the incidence of dementia reduced. When silica dust of finely divided crystalline is inhaled, it may lead to lung cancer, bronchitis, or silicosis, because of the lodging of dust in the lungs. Also, when fine particles of Silica are inhaled in excessive quantities, it increases the risk of lupus and rheumatoid arthritis.

FAQ (Frequently Asked Questions)

1. Where is the silicon dioxide found in nature?

Silicon dioxide produces widely in nature. The ATSDR (Agency for Toxic Substances and Disease Registry) just gives an idea of how common this compound is.

It is easy to recognize by its common name and quartz, which makes up about 12% of the earth’s crust. Silicon dioxide, however, also occurs naturally in everything from water and animals to plants.

The Silica sand covers various beaches, and it makes up most of the earth’s rocks. In fact, silica-containing minerals or Silica itself can make up more than 95% of the earth’s crust.

Also, Silicon dioxide exists in numerous plants that regularly humans consume, including, 

  • Dark and leafy greens

  • A few kinds of cereal and grains, like oats and brown rice

  • vegetables, like bell peppers and beets

  • Also, alfalfa

Also, Silicon dioxide naturally occurs in the human body, though it is still unclear on the exact role it plays.

2. Why is Silicon Dioxide used in food and supplements?

Naturally, Silicon dioxide is found in many plants, including,

  • Brown rice

  • Leafy green vegetables

  • Beets

  • Alfalfa

  • Bell peppers

  • Oats

In addition, Silicon dioxide is also used in many foods and supplements. In the form of a food additive, it serves as an anti-caking agent to avoid clumping. It is used to prevent different powdered ingredients from sticking together in supplements.

With many food additives, consumers often have some concerns on silicon dioxide as an additive. Numerous studies, however, suggest there’s no cause for these concerns.