Mica is a natural occurring mineral that is based on a collection of silicate minerals and composed of varying amounts of potassium, iron, aluminum, magnesium and water. It is found having thin-sheet like or plate-like structure with various composition and physical properties. Mica forms flat six-sided monoclinic crystals along with an extraordinary split in the direction of larger surfaces. This allows the mineral to be easily cleaved into optically flat films. High in silica, this stone has the extensive capacity to remain elastic and tough even at high temperatures. This helps the people to handle and work with the stone in those places with high and humid temperatures. A superior insulator and a biaxial birefringent crystal, Mica possesses average refractive index and its visible spectrum is about 1.6. Due to this nature Mica can be used to cause a point delay between two orthogonal elements of an input linear polarization and therefore can also be used as a retardation device. However, the birefringence is not constant and because of this very reason the optical and physical thickness will vary. It has the absorption of 2 to 5% in the perceptible range. The best part is Mica can resist nearly all mediums like chemicals, acids, gasses, alkalis, and oils
Properties Of Mica
Physical:Mica is translucent, easily split into thin films along its cleavage, optically flat, colorless in thin sheets, elastic and incompressible.
Chemical: It is a compound hydrous silicate of aluminum, which also contains iron, magnesium, potassium, sodium fluorine, lithium and also few traces of numerous other elements. It is constant and entirely static to the action of water, acids (except for hydrofluoric and concentrated sulphur), alkalies, conventional solvents, bases, and oil. It remains almost unchanged by atmospheric action.
Electrical: Mica has the exclusive combination of uniform dielectric steadiness, capacitance stability, enormous dielectric power, high Q factor and lower power loss, high electrical resistance and low temperature coefficient. It is highly regarded for its resistances to arc and corona discharge without causing any lasting injury.
Thermal: It is highly fire proof, incombustible, non- flammable, infusible, and also can resist temperatures of up to 1000 degrees Celsius/1832 degrees Fahrenheit. However this depends on the type and variety of Mica used. It has excellent thermal stability, lower heat conductivity, and can be easily exposed to high temperatures without visible effect.
Mechanical: Mica is highly tough, having high tensile strength, elastic, and along with being flexible. It has immense compression power and can be machined, die-punched, or hand cut.
Joint Compound
The primary use of ground mica is in joint compound used to finish seams and blemishes in gypsum wallboard. The mica serves as a filler, improves the workability of the compound and reduces cracking in the finished product.
Paint
Ground mica is used as a pigment extender in paint. It helps keep pigment in suspension; reduces chalking, shrinking and shearing of finished surface; reduces water penetration and weathering and brightens the tone of colored pigments. In some automotive paints tiny flakes of mica are used to produce a pearlescent luster.
Drilling Mud
Ground mica is an additive to drilling mud that helps to seal porous sections of the drill hole to reduce circulation loss.
Plastics
The auto industry uses ground mica to improve the performance of plastic parts. In plastics, particles of ground mica serve as an agent to absorb sound and vibration. It can also improve mechanical properties by increasing stability, stiffness and strength.
Rubber
Ground mica is used as an inert filler and mold release agent in the manufacture of molded rubber products such as tires and roofing. The platy grains if mica act as an antisticking agent.
Asphalt Roofing
Dry-ground mica is used as a surface coating on asphalt shingles and rolled roofing. The flat mica particles coat the surface and act as an antistick agent. The mica does not absorb the asphalt and stands up well to weathering.
Cosmetics
Some of the highest quality ground mica is used in the cosmetics industry. The pearly luster of ground mica makes it an important ingredient in blushes, eyeliner, eye shadow, foundation, hair and body glitter, lipstick, lip gloss, mascara, and nail polish.
Uses of Sheet Mica
Sheet mica is used in a number of electrical and electronic appliances in different shapes and sizes. As an insulating material it is used in equipment like condensers, transformers, sheostats, radio and electronic tubes and radar circuits. It is used in the form of washers, discs, tubes and plates. Nowadays mica is finding increasing use in equipment that encounters very high temperatures like rockets, missiles and jet engine ignition system. It is reported that in the manufacture of Telestar transmission satellites, good use of mica has been made. Phlogopite is used in spark plugs. Sheet mica, however, is not always available in required size as demanded by the industry. Great progress has been achieved in making built-up mica called micanite. Mica films are placed with alternate layers of binding materials like shellac, alkyl, or silicon resin and then pressed and baked. Micanite is in common use now. It is convenient to cut or punch micanite according to requirements. In the electronic-field, natural mica is mainly used in the manufacture of capacitors such as bridge-spacers in electronic valves and as panel-board where heat-resistance and low-loss peoperties at high frequencies are required. In such delicate equipment, mica of thinness varying from 0.015 inch and below are used. The mica of thickness in the range of 0.007" to 0.015" is used in bridge-spacers. Even thinner films, between 0.004" to 0.006", are used as backing plates for capacitors and further thinner films in the range of 0.0007" to 0.002" as dielectric. The splittings of such fine thickness are made with the help of pin and knife only.
