Silicon Dioxide - Structure, Properties, Production, Application and Uses
What is Silicon Dioxide?
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 \[SiO_{2}\], 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 a long-term progressive lung injury, silicosis. (\[NCIO_{4}\]). The \[SiO_{2}\] 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 odourless 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.
\[SiO_{2}\] 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 \[SiO_{2}\] structure is represented in the following way.
If we notice properly, each silicon atom is bridged to its neighbour by an oxygen atom. Remember that this is just a tiny part of a giant \[SiO_{2}\] structure that extends on all three dimensions.
Silicon Dioxide Properties
The basic \[SiO_{2}\] properties of both physical and chemical are given below.
Physical Properties of \[SiO_{2}\]
Silicon dioxide is transparent to grey, crystalline, odourless, 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 \[SiO_{2}\]
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.
\[Na_{2}Si_{3}O_{7} + H_{2}SO_{4} \rightarrow 3SiO_{2} + Na_{2}SO_{4} + H_{2}O\]
Silicon Dioxide Reactions
Silica is converted into silicon by reducing carbon.
When fluorine reacts with silicon dioxide, it produces \[O_{2}\] and \[SiF_{4}\].
Silicon dioxide also reacts with hydrofluoric acid to form hexafluorosilicic acid (\[H_{2}SiF_{6}\]).
\[SiO_{2} + 6HF \rightarrow H_{2}SiF_{6} + 2H_{2}O\]
Preparation of Silicon Dioxide
Most of the silicon dioxide is extracted even from quartz mining, it can also be prepared using acid neutralisation of an aqueous alkali metal - silicate solution. This kind of method is known as a wet process and forms amorphous \[SiO_{2}\] particles.
\[Na_{2}Si_{3}O_{7} + H_{2}SO_{4} \rightarrow 3SiO_{2} + Na_{2}SO_{4} + H_{2}O\]
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.
\[SiCl_{4} + 2H_{2} + O_{2} \rightarrow SiO_{2} + 4HCl\]
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 is various Silicon dioxide used 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, \[SiO_{2}\] is the main component of optical fibres. Silicon dioxide is extensively used as a precursor to obtaining glass and silicon by the reaction given below.
\[SiO_{2} + 2C \rightarrow Si + 2CO\]
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.
FAQs on Silicon Dioxide
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.
3. State the benefits of silicon dioxide.
There are a number of benefits of silicon dioxide. They are as follows:
One of the major uses of silicon dioxide lies in the construction and building industry where it is used for making ceramics, concrete, etc.
It is a raw material with the use of which various types of glasses are made.
It avoids clumping as it serves as an anti-caking agent in supplements.
It also serves as an additive agent that can be further used for preservatives.
When consumed through food, silicon dioxide helps to strengthen your bones and increase your bone mineral density.
It is also highly utilised in quite a lot of high tech equipment which includes computer chips, transistors, solar panels, etc.
4. What are some disadvantages of silicon dioxide?
Some of the disadvantages and health risks associated with silicon dioxide are as follows:
If the dust particles of silica are inhaled for a prolonged period of time, then it can lead to some serious health issues. Some of these issues include silicosis, which is an irreversible lung disease, an increased risk of tuberculosis, and chronic obstructive pulmonary disease or COPD.
Studies have also shown that exposure to respirable crystalline silica leads to an increased risk of getting kidney disease.
5. How is silicon dioxide formed?
The chemical compound that is found in silicon dioxide, i.e., \[SiO_{2}\] is formed when silicon is exposed to oxygen. Most of the time, silicon dioxide is recognised in the form of quartz, as a result of which, most of it is also extracted through the process of quartz mining. It can also be prepared through another method that tends to involve the acid neutralisation of a silicate solution which happens to be an aqueous alkali metal. There is yet another method that can be used but this one gives pyrogenic silica as its end result. This can be done by having silicon tetrachloride, a process of silence combustion, in an oxygen-hydrogen burner.
6. Which elements does silicon dioxide react with? What is molecular silicon dioxide?
Silicon dioxide tends to react with all the halogens in order to form silica tetrahalides. For instance, some of the elements it reacts with include chlorine, bromine, fluorine, and iodine.
It also tends to react with hydrofluoric acid and as a consequence/result, forms hexafluorosilicic acid.
The molecular form of \[SiO_{2}\] has a linear and highly symmetrical structure, similar to that of \[CO_{2}\]. When you combine silicon monoxide (SiO) with oxygen in an argon matrix, you get silicon monoxide as a result. And if oxygen reacts with matrix isolated dimeric silicon monoxide \[(SiO_{2})_{2}\] then you get the dimeric silicon dioxide \[(SiO_{2})_{2}\]. And in this dimeric silicon dioxide, there are two atoms of oxygen, bridging between the atoms of silicon.
7. What is silica gel? What happens if you ingest it?
The porous and amorphous form of silicon dioxide (silica), is known as silica gel. It comprises a tridimensional framework of alternating the atoms of silicon and oxygen with nanometer-scale pores as well as voids. These voids may consist of water or some fluid or may be filled with vacuum or gas, and this tridimensional framework is also an irregular one. The formula of silica gel is \[SiO_{2}\]. It mainly serves as a drying agent or a desiccant and is placed in little packets. This is because it helps to avoid the particular commercial product or food item from getting damaged. The silica gel absorbs some of the moisture in case there is excess, and if there’s a lack of it and the air starts to become too dry, then it releases some of the water that it earlier absorbed.
Silica gel is considered safe to touch and isn’t a harmful or toxic ingredient. And generally, accidentally eating silica gel doesn’t flare up any serious concerns, However, in certain unfortunate cases, swallowing silica gel is most likely to cause dehydration, which may or may not lead to an upset stomach, itchiness and/or irritation in the nose and throat, nausea followed by puking, and constipation. And if an individual ends up accidentally ingesting silica gel beads that have been coated in a shade of blue or pink (cobalt chloride), then they should seek immediate medical attention.
