Electrical Insulators

Electrical insulators are materials that do not allow an electric current to flow through them easily. Insulators have high electrical resistance and low electrical conductivity. This property makes insulators useful in many electrical applications where we want to prevent the flow of electric current, such as in electrical safety equipment, electrical insulation, and electronics.

Examples of electrical insulators include rubber, glass, porcelain, mica, plastic, and air. The electrons in insulators are not able to move freely, which means that electric current cannot pass through them easily. Insulators can also have other useful properties, such as high melting points, high thermal resistance, and resistance to chemicals and moisture.

In electrical systems, insulators are often used to separate conductors from each other and to prevent electrical current from flowing where it is not supposed to go. For example, electrical wires are often coated in an insulating material to prevent electric shocks and short circuits.

Theory of Electrical Insulators

The behavior of electrons in insulators can be explained by the theory of band structure. According to this theory, atoms in a solid are arranged in a periodic lattice structure. The electrons in the atoms occupy energy levels, or “bands,” that are closely spaced together. In insulators, the valence band, which contains the electrons that participate in chemical bonding, is completely filled, while the conduction band, which is empty, is separated by a large energy gap from the valence band. This occurs because the “valence” band containing the highest energy electrons is full, and a large energy gap separates this band from the next band above it.

To conduct electricity, electrons must move from the filled valence band to the empty conduction band. In insulators, the energy required to move electrons across the energy gap is very high, so very few electrons are able to move to the conduction band, and thus, the material is a poor conductor of electricity. Most insulators have a large band gap. This occurs because the “valence” band containing the highest energy electrons is full, and a large energy gap separates this band from the next band above it. There is always some voltage (called the breakdown voltage) that gives electrons enough energy to be excited into this band. Once this voltage is exceeded, electrical breakdown occurs, and the material ceases being an insulator, passing charge. This is usually accompanied by physical or chemical changes that permanently degrade the material and its insulating properties.

When the electric field applied across an insulating substance exceeds in any location the threshold breakdown field for that substance, the insulator suddenly becomes a conductor, causing a large increase in current, an electric arc through the substance. Electrical breakdown occurs when the electric field in the material is strong enough to accelerate free charge carriers (electrons and ions, which are always present at low concentrations) to a high enough velocity to knock electrons from atoms when they strike them, ionizing the atoms.

In a solid, the breakdown voltage is proportional to the band gap energy. Even a vacuum can suffer a sort of breakdown, but in this case the breakdown or vacuum arc involves charges ejected from the surface of metal electrodes rather than produced by the vacuum itself.

In addition, all insulators become conductors at very high temperatures as the thermal energy of the valence electrons is sufficient to put them in the conduction band.

The band structure theory also explains other properties of insulators, such as their transparency to light. In insulators, the energy required to excite electrons from the valence band to the conduction band is in the ultraviolet range, so visible light does not have enough energy to excite electrons and is therefore transmitted through the material.

Examples of 10 Good Electrical Insulators

Insulator	Description
Glass	Transparent or translucent solid material that is often used in windows, lenses, and laboratory equipment.
Ceramic	Non-metallic, inorganic solid material that is often used in electrical components, such as capacitors and resistors.
Rubber	Elastic, insulating material that is often used in electrical wiring and cables.
Paper	Thin material made from wood pulp that is often used in electrical insulation and packaging.
PVC	Synthetic plastic material that is often used in electrical cable insulation and plumbing pipes.
Teflon	Synthetic fluoropolymer material that is often used in high-temperature and high-frequency electrical applications.
Epoxy	Thermosetting polymer material that is often used in electrical and electronic applications, such as circuit boards and coatings.
Bakelite	Thermosetting plastic material that was widely used in the early 20th century for electrical insulators and other applications.
Oil	Liquid insulating material that is often used in electrical transformers and other high-voltage equipment.
Air	Gaseous insulating material that is often used as a dielectric medium in capacitors and other electrical devices.

Material with highest dielectric strength

The material with the highest dielectric strength is a synthetic diamond, also known as diamond-like carbon or DLC. It has a dielectric strength of up to 10 million volts per millimeter (V/mm), which is several times higher than the dielectric strength of air.

Synthetic diamonds are created by depositing a thin film of carbon onto a substrate using various techniques such as chemical vapor deposition or physical vapor deposition. The resulting material is highly resistant to electrical breakdown and can withstand very high electric fields.

However, synthetic diamonds are expensive and difficult to produce in large quantities, so they are not commonly used as electrical insulators. Other materials with high dielectric strengths, such as ceramics and polymers, are often used in practical applications.

Classification of Materials according to Electrical Conductivity

Materials can be classified into different categories based on their electrical conductivity. Here are some common categories:

1. Conductors: Materials with high electrical conductivity, such as metals and some types of solutions, are known as conductors. They are able to carry an electric current with minimal resistance and are commonly used in electrical and electronic applications.
2. Insulators: Materials with low electrical conductivity, such as plastics, rubber, and glass, are known as insulators. They are not able to carry an electric current easily and are commonly used to isolate and protect electrical components.
3. Semiconductors: Materials that have intermediate levels of electrical conductivity, such as silicon and germanium, are known as semiconductors. They can be used to control and manipulate the flow of electric charge and are used extensively in electronics and computer applications.
4. Superconductors: Materials that have zero electrical resistance at very low temperatures are known as superconductors. They are able to carry electric current without any loss of energy and are used in specialized applications such as MRI machines and particle accelerators.
5. Ionic conductors: Materials that conduct electricity through the movement of ions rather than electrons, such as some types of salts and electrolytes, are known as ionic conductors. They are commonly used in batteries, fuel cells, and other electrochemical devices.

Generally, most metals have high conductivity (which is another way of saying metals tend to be conductors) because the electrons in their outermost shell can move easily. Non-metals tend to have low conductivity.