Mica is a naturally occurring mineral that has been used in electrical and thermal insulation since many years. Mica is a generic term applied to a group of Complex alumino silicate minerals having a sheet or plate like structure with different composition and physical properties.
It is a complex hydrous silicate of aluminium, containing potassium, magnesium, iron, sodium fluorine and/or lithium and also traces of several other elements. It is stable and completely inert to the action of water, acids (except hydro-fluoric and concentrated sulphuric) alkalies conventional solvents, oil and virtually unaffected by atmospheric action.
NATURE OF MICA
Mica appears in a transparent form, colorless in thin sheets, resilient and incompressible. Mica can be easily split into optically flat films. When split into thin films, they remain tough and elastic even at high temperature. Mica possesses some of the most outstanding combinations of chemical, physical, electrical, thermal and mechanical properties which are not found in any other product. These properties make it an excellent Insulator. Mica has a high dielectric strength and excellent chemical stability.
Mica has the unique combination of great dielectric strength, uniform dielectric constant and capacitance stability, low power loss (high Q factor), high electrical resistivity and low temperature coefficient and capacitance. It is noted for its resistances to arc and corona discharge with no permanent injury.
Mica is fire proof, infusible, incombustible and non- flammable and can resist temperatures of 600 deg-C to 900 deg-C, depending on the type of mica. It has low heat conductivity, excellent thermal stability and may be exposed to high temperatures without noticeable effect.
Mica is relatively soft and can be hand cut, machined or die-punched. It is flexible, elastic and tough, having high tensile strength.
CLASSIFICATION OF MICA
Mica is classified into Muscovite Mica and Phlogophite Mica.
Muscovite mica has greater dielectric strength than any other insulating material. It surpasses all mica in dielectric strength, thermal endurance, mechanical strength, moisture resistance, transparency, flexibility, resilience, toughness and perfection of cleavage and is therefore recognized as the best mica for electrical and electronics devices. It is almost insensitive to atmospheric weathering and offers greater resistance to outside Chemical influence. This type of mica stand up to 900-C.
It is available in two colors: Ruby and Green.
Phologophite Mica is a hydrous potassium magnesium aluminium silicate. Here the calcination temperature is reached at about 1000-C. Generally speaking, Phologophite mica is softer than Muscovite micas and this for instance makes it more suitable for the manufacture of commutator micanite used in commutators of flush running designs.
It is available in three colors: Dark Green, Light Green and Golden. The best quality of Phlogophite mica is found in Madagascar.
