Mica: a traditional material for the electrotechnical industryJohn Moot
What is mica?
Mica is so called because of its gleaming and shiny appearance. The different types of mica can be easily distinguished by their colour. Muscovite has a light and phlegopite a dark appearance. Mica, also called mica, is a mineral extracted from mines. It belongs to the monoclinic crystal system and consists of alkali-containing aluminium silicates of various compositions. Among a multitude of natural mica types, only two are considered for technical use: muscovite and phlogopite. Muscovite, also called potassium mica, is a potassium aluminium double silicate. The colour is ruby red, also white, green or brown. Phlogopite, also called magnesia mica, is a potassium-magnesium-aluminium-iron double silicate. The colouring is similar to amber, after which it is also called amberg mica.
Historical facts about mica
Mica were already mentioned in 1546 by the mineralogist Georgius Agricola. Where mica was readily available and inexpensive, but glass was too expensive, the mineral was used for window panes, especially in rural areas. In the 20th century mica was first examined with X-rays by Charles-Victor Mauguin. Mica means weakly glowing or shining. But from time immemorial, the name was used to refer to a dazzler who does not keep his promises. Therefore, some types of mica are also derogatorily called cat silver or cat gold. In English this mineral is called mica, from lat. mica = crumb (frequent occurrence in small leaves) or micare = sparkle.
Occurrence of mica
Mica is found almost all over the world, but it is worthwhile mining in India, South Africa, Latin America and Russia, where it is embedded in blocks or slabs of primary rock.
Properties and technical data of mica
Mica has very good electrical insulation and good thermal conductivity properties. But also very good tracking and dielectric strength. Dielectric constant 5…8
Mica are silicates, i.e. silicon compounds. Mica always has two-dimensional layer structures. Strong bonding forces act within the layers, but the layers are weakly bonded to each other. This explains the good cleavability.
Application of mica
Because of its above mentioned properties mica is an optimal insulator for mounting power transistors on cooling plates. Furthermore it is used as insulator holder of heating elements because of its heat resistance. The HF values are also remarkable, therefore it is used as dielectric in high frequency capacitors. In the insulation system of high-voltage machines, various components, which must be optimally matched to each other, are used. High-quality mica products (mica tapes and mica plates) are used as main and partial conductor insulation.
Main applications for components made of mica are found in the following areas:
- Construction of induction, arc and high frequency furnaces
- High voltage applications
- High temperature applications
- Sealing industries (e.g. oil & gas distribution)
- Heating elements for electrical and thermomechanical applications
Delivery forms of mica
We supply tapes and laminates made of mica paper as well as milled and turned parts made of mica plates.
Tests for mica
On customer request we carry out specified electrical, mechanical and optical tests on mica products such as milled parts or strips.
Disposal of mica
The disposal is unproblematic.
8 properties that make mica stand out:
- High dielectric strength
- High dielectric resistance
- Low dielectric losses
- High temperature and thermal shock resistance
- Good transparency or optical purity
- Resistance to acids and oils
- Mechanical cleavability down to the µm range
- Good processability