MICA - the mineral that glitters with a glimmer of hope responsible for shine of every women's face and brilliant metallic colors in cars & automobiles and the wonder insulation material. The name "MICA" is derived from latin word MICARE which means ' to shine or glitter.
Mica is a generic term applied to a group of Complex aluminosilicate minerals having a sheet or plate like structure with different composition and physical properties. All mica form flat six-sided monoclinical crystals with a remarkable cleavage in the direction of large surfaces, which permits them to 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.
Physically:Mica is transparent, optically flat, easily splittable into thin films along its cleavage, colourless in thin sheets, resilient and incompressible.
Chemically: 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.
Electrically: 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.
Thermally: Mica is fire proof, infusable, incombustible and non- flammable and can resist temperatures of 600-C to 900-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.
Mechanically: Mica is relatively soft and can be hand cut, machined or die-punched. It is flexible, elastic and tough, having high tensile strength.
Typical End uses of natural sheet mica :
· Electrical Apparatus
· Electric Heating Appliances
· Electrical Control
· Electrical Lighting Equipment
· Industrial Electric Heating Appliances
· Mechanical Uses
· Miscellaneous Electrical Uses
· Radio, Radar, Television etc.
· Motors and Generators
Mica deposits are found in India, Africa, Brazil and China.The principal deposits of Mica in India are found in Bihar, Rajasthan, and Andhra Pradesh.Mica is again classified into Muscovite Mica and Phlogopite 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.
Phologopite Mica is a hydrous potassium magnesium aluminium silicate. Here the calcination temperature is reached at about 800 C. Generally speaking, Phologopite 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.
Muscovite mica may be divided into two colour groups : Ruby and green.
Ruby Muscovite : Colour ranges from an almost white through pink to a light ruby and into shades of brownish ruby and brown.
Green Muscovite : Ranges from light to pale green through yellowish and olive green to a dark green. Colour as such has less significant influence on quality. Still ruby muscovite is generally preferred especially in the higher qualities as it is considered to be superior to green mica for applications requiring high dielectric strength and low power loss (or high Q). Ruby muscovite is harder than green mica, has excellent cleavage permitting it to be split into the thinnest desired film without the risk of cracking.