Silicate vs Silicone
Silicates and silicones are two important inorganic compounds that have a variety of uses and applications. While their names may sound similar, they have distinct chemical structures and properties. In this article, we will take a closer look at what silicates and silicones are, how they are produced, their key differences, and their common applications.
Silicates are compounds containing silicon, oxygen, and one or more metals. The silicon and oxygen atoms join together to form anionic groups called silicate anions. These anions can join with metal cations to create silicate salts and minerals. The most common metal cations bound to silicates are sodium, potassium, calcium, magnesium, iron, and aluminum.
Some examples of silicate compounds include:
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Sodium silicate (Na2SiO3) - known as water glass
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Calcium silicate (CaSiO3) - a common component of cements
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Aluminosilicates - found in clays and zeolites
In nature, silicates make up most of the Earth's crust. Quartz, feldspar, mica, and clay minerals are all silicates. Silica (SiO2), or silicon dioxide, is the simplest silicate and the most abundant compound in the crust.
Silicates can be classified according to their structure and geometry.
Some major groups include:
- Orthosilicates - each silicon atom is surrounded by 4 oxygen atoms in a tetrahedral arrangement. Examples are olivine and garnet.
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Sorosilicates - two tetrahedral [silicate] groups share an oxygen atom. Hemimorphite is a sorosilicate.
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Inosilicates - silicate tetrahedra form single chains. Amphibole asbestos is an inosilicate.
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Phyllosilicates - silicate sheets are stacked. Micas and clays belong to this group.
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Tectosilicates - 3D frameworks of silicate tetrahedra. Quartz and feldspars are tectosilicates.
What is Silicone?
Silicones, also known as polysiloxanes, have a similar name but a very different chemical structure from silicates. The silicone backbone consists of alternating silicon and oxygen atoms, with side chains attached to the silicon. The general formula is (R2SiO)n where R can be hydrogen, methyl, ethyl or other hydrocarbon groups.
The most common silicone is polydimethylsiloxane (PDMS) where the R groups are methyl. PDMS has an inorganic silicone-oxygen backbone and organic methyl side groups attached to silicon. This gives unique properties compared to fully inorganic or fully organic compounds.
Silicones are man-made polymers derived from silicon, carbon, oxygen and hydrogen. They are created by reacting chlorosilanes with water in a hydrolysis reaction. For example, dimethyldichlorosilane (CH3)2SiCl2 reacts with water to ultimately produce PDMS chains:
(CH3)2SiCl2 + 2H2O → (CH3)2Si(OH)2 + 2HCl
(CH3)2Si(OH)2 →-(CH3)2SiO- + H2O
Silicones can exist as oils, gels, elastomers, resins and rubbers depending on their molecular weight and structure. Their properties make them useful as sealants, adhesives, lubricants, and insulators.
Is Silicone Made from Silica?
Silica (silicon dioxide) is the starting material used to produce elemental silicon metal. This silicon is then reacted with methyl chloride to create chlorosilanes like dimethyldichlorosilane. So in that sense, silicone is derived from silica as the original silicon source.
However, the production of silicone polymers does not directly use silica. Silicones have a different Si-O-Si backbone structure compared to silicates. The silicone synthesis reactions convert silica to silicon metal, and then chlorosilanes, before creating silicone polymers.
So while silicone starts from silica, it goes through many chemical transformations. Adding organic side chains to silicon creates very different properties compared to inorganic silicates.
What is Silicone Used For?
Silicones have a unique set of properties based on their inorganic-organic structure. Some key properties include:
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Thermal stability - silicones maintain properties at high and low temperatures
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Chemical resistance - silicones are not degraded by water or oils
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Flexibility - silicone rubbers can repeatedly stretch and compress
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Low surface tension - silicones spread readily and serve as good release agents
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Moisture resistance - silicones repel water and moisture
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Electrical insulation - silicones resist conduction of heat and electricity
These properties make silicone ideal for high performance applications:
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Heat resistant insulators for appliances and electronics
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Mold making and casting of plastics and rubbers
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Lubricants for aerospace and automotive
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Water repellent coatings on fabrics and paper
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Sealants for construction, aviation and food packaging
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Medical implants due to biocompatibility
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Beauty products due to texture, feel and hydration
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Food molds and bakeware able to withstand oven temperatures
PDMS is the most widely used silicone fluid across many industries. Its inertness makes it safe for various medical and food applications.
What is the Difference Between Silicone and Silicates?
Silicones and silicates show some clear differences based on their distinct chemical structures:
Silicones have a silicone-oxygen (-Si-O-) backbone while silicates have silicon-oxygen (Si-O) anionic structures.
Silicones contain hydrocarbon (methyl, ethyl) side chains attached to silicon. Silicates have metal cations (Na+, Ca2+, Mg2+) attached to the silicate anions.
Silicones are synthetic organic-inorganic polymers made from silicon, carbon, oxygen and hydrogen. Silicates are naturally occurring inorganic minerals containing silicon, oxygen and metals.
Silicones exhibit properties like thermal stability, flexibility and water repellency due to their unique chemical structure. These traits differ substantially from silicate properties.
Silicones have lower melting points and are degraded above 200°C. Silicates have very high melting points and can withstand very high temperatures.
Silicones are hydrophobic and repel water. Many silicates are hydrophilic and can absorb moisture.
Silicones serve as lubricants, insulators, coatings, gels and sealants. Silicates are primarily used in glass, ceramics, cements and refractories.
So while their names seem similar, the different atomic arrangements of silicone and silicate lead to very different compound classes with distinct chemical and physical properties. Silicones find specialized uses in high performance applications due to attributes arising from their unique inorganic-organic structure.
Conclusion
Silicates and silicones represent two important inorganic material classes with many applications. Silicates are naturally occurring compounds containing silicon-oxygen anions bound to metal cations. Quartz, clay, mica and asbestos are common silicate minerals. Silicones are synthetic polymers made of silicon, oxygen, carbon and hydrogen. Their unique structure provides properties like high temperature stability, chemical resistance and flexibility. Silicones are produced industrially from silicon and chlorosilanes rather than directly from silica. From adhesives to medical devices, silicones find many uses where their special properties are needed. While their names are similar, silicates and silicones have distinct structures and chemistries making them very different compound classes.