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).
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
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
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
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.