what is types Of Mica

1. Muscovite mica- KAl2(AlSi3O10)(OH)2 - 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. Muscovite Mica is harder than Phlogopite Mica.

Muscovite Mica is the most commonly used Mica in electrical insulation and since it has the best electrical properties of all Mica. High quality Mica cleaves the easiest and into the thinnest sheets and with the fewest imperfections that could be seen at the atomic or near atomic scale with AFM or TEM instrumentation. Muscovite Mica is commonly divided into two color groups:

Ruby : varies in color from clear to pink to red / brown
Green: varies in color from pale green to olive to dark green

Ruby Muscovite : Color ranges from an almost white through pink to a light ruby and into shades of brownish ruby and brown. Ruby Mica has excellent cleavage capabilities permitting it to be split into the thinnest desired film without the risk of cracking.

Green Muscovite : Ranges from light to pale green through yellowish and olive green to a dark green. Color 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 and green Mica have excellent cleavage permitting it to be split into the thinnest desired film without the risk of cracking. Use of ruby and green Mica is a matter of preference and application.

2. Phologopite Mica - KMg3(AlSi3O10)(OH)2 - is a hydrous potassium magnesium aluminium silicate. Here the calcination temperature is reached at about 800 C. Generally speaking, Phlogopite Mica is softer than Muscovite mica and this for instance makes it more suitable for the manufacture of commutator micanite used in commutators of flush running designs.



Phlogopite Mica is commonly called amber mica and varies in color from light silver to dark brown. Phlogopite Mica has poor electrical properties and chemical resistance in comparision to Muscovite mica.




Chemical formula : KAl2(AlSi3O10)(OH)2

Luster : nonmetallic (glassy)
Cleavage: one perfect plane
Hardness: 2 - 2.5
Streak: none
Diagnostic hints: Muscovite mica is most easily identified by its characteristic cleavage and light color. The only other minerals that it could be confused with is Biotite, which is always dark black, or Chlorite, which is generally a green-black color. The hardness of Muscovite will seem to be less than 2.5 due to slippage on cleavage planes.

What is Mica?
           
Mica is a natural valuable mineral product applied to a group of a complex aluminosilicate minerals having a sheet or plate like structure with different chemical compositions and physical properties. All micas form flat six sided monoclinical crystals with a remarkable cleavage in the direction of the large surfaces, which permits them to split easily into optically flat films, as thin as one micron in thickness. When split into thin films, they remain tough and elastic even at high temperature.

What makes micas so important to command such a unique position ? Because it had been gifted with exceptional values. It possesses some of the most outstanding combination of chemical, physical, electrical, thermal and mechanical properties which are not found in any other product.
         
Processing
         
The ordinary mica crystals as they come out of a mine is in form of rough books or lumps of irregular shape, size and thickness, associated with impurities and structural imperfections. They have to undergo a long operation of cutting, sorting and processing from crude to commercial quality. The waste resulting from the production of crude to commercially useful sheet mica forms about 90 per cent Some times even the total output of mica from a mine is sold as scrap mica and it can be used as Mica Scrap or can be used for Grinding Mica Powder.
       
No machine has yet been designed to process mica mechanically. The processing technique, therefore, involves only a pair of hands, eyes and a simple knife. The operations performed consists of cobbing or cleaning the crude crystals as extracted from the mine with its associated impurities; rifting or splitting the cobbed mica into usable sheets by sickle and then by sharp knife removing major flaws and structural imperfections, such as cracks, holes, reeves, crossgrains and other physical defects to obtain the maximum usable area with minimum wastage. The trimming of mica is a skilled hand-operation in which cracks and imperfections are removed at the edges of the sheets using a knife while saving the best area of usable sheet. The knife-dressed sheet mica of irregular polygonal shapes is finally graded into different standard sizes and commercial qualities before they are offered for marketing.
       
Classification
     
For commercial and industrial purpose natural mica are mainly divided into three catagories,viz :

1. Processed Mica  2. Fabricated Mica  3. Manufactured Mica.


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What Is Mica ?
Mica is a naturally occurring mineral, based on a group of silicate minerals composed of varying amounts of aluminum, potassium, magnesium, iron and water having thin sheet-like or plate-like structure with different composition and physical properties. All Mica form flat six-sided monoclinic crystals with a remarkable cleavage in the direction of large surfaces, which permits them to be easily cleaved into optically flat films. When cleaved into thin films, they remain tough and elastic even at high temperatures. Mica possesses some of the most outstanding combinations of chemical, physical, electrical, thermal and mechanical properties which cannot found in any other insulating product.

Mica is a biaxial birefringent crystal. Its average refractive index in the visible spectrum is about 1.6. Because of its birefringence, it can be used to cause a phase delay between two orthogonal components of an input linear polarization and thus can be used as a retardation device. For same physical thickness, optical thickness of Mica can vary because its birefringence is not constant. Mica has absorption of 2 to 5% in the visible spectrum.

Physically: Mica is transparent, optically flat, easily split into thin films along its cleavage, colorless in thin sheets, resilient and incompressible.

Chemically: It is a complex hydrous silicate of aluminum, 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 hydrofluoric and concentrated sulphuric), bases, 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 resistance or resitivity 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, non- flammable and can resist temperatures of up to 1000 degrees Celsius/1832 degrees Fahrenheit, 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 highly elastic, flexible and tough, having high tensile strength. It has great compression strength and can be hand cut, machined or die-punched.

Typical End uses of natural sheet Mica:

• Electrical apparatus, heaters, hair dryers, etc.
• Electric heating appliances
• Electrical controls
• Electrical lighting equipment
• Industrial electric heating appliances
• Radio, radar, television etc.
• Motors, generators, load centers, etc.
• Transformers