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Mica

What is Mica ?
The mica is group of sheet silicate (phylloscilicate) mineral that includes several closely related materials having highly perfect basal cleavage. The highly perfect cleavage, which is the most prominent characteristic of mica, is explained by the hexagonal sheet-like arrangement of its atoms.

The word "mica" is thought to be derived from the Latin word micare, meaning "to glitter", in reference to the brilliant appearance of this mineral (especially when in small scales).

Uses :
In the manufacturing of electronic devices, a mica insulator is a die-cut punched insulator of natural or "block" mica splittings.

Mica slices are used in electronics to provide electric insulation between an electronic component which can generate heat and the heat sink used to cool it. Mica is used because it can be split into very thin slices, and this keeps its thermal resistance low while retaining sufficient dielectric strength to prevent current from flowing across it at moderate voltages. The insulation is usually necessary when the heat sink is earthed while the electronic component's metal surfaces will be connected to a power supply or signal line. If they were in direct contact this could form a short circuit. Heat sink insulation can also be necessary to prevent the heat sink from acting like an antenna if the component is connected to a rapidly varying signal.

The same term ("mica insulator") is sometimes used by technicians to designate a synthetised gum (usually blue or grey) used for the same purpose, but not actually composed of the silicate mineral at all.

Micas are a group of aluminium phyllosilicate minerals which are found worldwide. Commercial deposits are found in India and Madagascar. It is mined in the form of "blocks" or rocks, which are then rifted to arrive at thin flexible natural mica splittings. When these are die-cut specifically for the transistor industry, the resultant product is called a "mica insulator".

Resin bonded mica or micanite or built up micanite from splittings or agglomerated micanite made from pulped mica powder are called micanites. All these products have additives, like resins, and the resultant products, while having inferior insulation properties to natural "mica insulators" are called micanites or micafoliums.

Properties, know Mica better :
Mica has a high dielectric strength and excellent chemical stability, making it a favoured material for manufacturing capacitors for radio frequency applications. It has also been used as an insulator in high voltage electrical equipment, and between the bars of commutators in Direct Current motors and generators. It is also birefringent and is commonly used to make quarter and half wave plates.

Illites or clay micas have a low cation exchange capacity or 2:1 clays. K+ ions between layers of mica prevent swelling by blocking water molecules.

Because mica can be pressed into a thin film, it is often used on Geiger-Muller tubes to detect low penetrating alpha particles.

Some brands of toothpaste include powdered white mica. This acts as a mild abrasive to aid polishing of the tooth surface, and also adds a cosmetically-pleasing glittery shimmer to the paste. The shimmer from mica is also used in makeup, as it gives a translucent "glow" to the skin or helps to mask imperfections.

Mica is used in the production of pearlescent pigments. Many metallic looking pigments are composed of a substrate of mica coated with another mineral, usually titanium dioxide (TiO2). The resultant pigment produces a reflective color depending on the thickness of the coating. These products are used to produce automobile paint, shimmery plastic containers, high quality inks used in advertising and security applications.

Mica sheets are used to provide structure for heating wire (such as in Kanthal or Nichrome) in heating elements and can withstand up to 900 C (1,650 F).

Another use of mica is in the production of ultraflat thin film surfaces (e.g. gold surfaces) using mica as substrate. Although the deposited film surface is still rough due to deposition kinetics, the back side of the film at mica-film interface provides ultraflatness, when the film is removed from the substrate.

Muscovite mica is the most common substrate for sample preparation for the atomic force microscope . Freshly-cleaved mica surfaces have been used as clean imaging substrates in atomic force microscope.

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