Mica
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Profile
Mica
is a general term for hydrated aluminum silicate
minerals with a layered structure and containing
metallic elements such as lithium, sodium, potassium,
magnesium, aluminum, zinc, iron, and vanadium.
Muscovite, biotite, phlogopite, and lepidolite are the
most common types of mica. Sheet and ground muscovite
and phlogopite are the most common forms of mica used as
industrial raw materials, and sericite is also used.
Muscovite is used in the greatest quantities, followed
by phlogopite. Mica is a good electrical insulator, is
transparent, separates into flakes easily, has excellent
chemical stability, has good elasticity, and can
maintain its superior physical and chemical properties
even at high temperature.
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Mica is an extremely important insulating
material, and is widely used in electronics, electrical
machinery, telecommunications, electrical devices,
aerospace, transportation, instruments, metallurgy,
building materials, light industry, defense, and other
high-tech areas. Due to growing demand for capacitors
and electrical device insulation and support materials
and dielectric materials starting in the 1970's, sheet
mica was overtaken by the replacement mica paper made
from crushed mica. The emergence of integrated circuits
induced a fundamental change in consumption; although
demand for sheet mica fell sharply, demand for crushed
mica rose steadily. Thanks to ongoing progress in
technology, mica is now used in a growing range of
applications, including building materials, geological
prospecting, lubricants, paints, foods, and cosmetics.
Crushed mica and sericite have very bright futures.
Chemical
composition: Muscovite has the chemical formula
KAl2(AlSi3O10)(OH)2; magnesium-rich muscovite has the
formula (Fe2+, g)(Fe3+,Al3+)(AlSi7O20)(OH)4; sericite
has the formula KAl2(Si,Al)4O10(OH,F) 2; and phlogopite
has the formula KMg3(AlSi3O10)(F,OH)2.
Mica is an aluminum silicate mineral with
a continuous tetrahedral silicate structure. Thin
flexible sheets are easily peeled from pieces of mica;
these sheets are soft, transparent, and colorless. Large
pieces of mica are translucent and sometimes grayish,
brownish, pale green, or pale red in color. Mica has a
vitreous to silky or pearly luster; hardness is 2.5-3
and specific gravity 2.75~3.0. It is resistant to acids.
Mica Powder
Profile
Mica's
superior dielectric performance includes relatively high
insulating strength and electrical resistance,
relatively low dielectric losses, and good anti-arcing
and anti-corona characteristics. It is resistant to high
temperatures and sudden temperature changes; it is heat
resistant, a thermal insulator, resistant to acids and
alkalis, compression resistant, and peels readily into
sheets. Furthermore, mica has a hard texture, good
mechanical strength, a good luster, stable physical and
chemical characteristics, and possesses excellent
flexibility, toughness, heat resistance, sound
insulating characteristics, and a small thermal
expansion coefficient. Sheets of mica are smooth and
glossy, and have a regular form, a high diameter to
thickness ratio, and strong bonding ability. Mica powder
has even better sliding and properties. Due to their
many excellent properties, mica and mica powder are
widely used in the electronics, aerospace, and
electrical machinery industries. They are also commonly
used in paints, coatings, plastics, linoleum, paper, oil
drilling, and cosmetics. The addition of mica to paint
can prevent UV radiation, light, or heat from damaging
the paint film, increase acid and alkali resistance,
enhance insulating performance, boost resistance to
freezing, increase corrosion resistance, toughness, and
tightness, reduce air permeability, and prevent spotting
and crazing. Mica powder can also be added to external
building materials to enhance rain resistance and
warming/cooling insulation. Mica powder mixed with
mineral wool and a resin coating can be applied to
concrete, stone, or brick outer walls for a decorative
effect. Mica powder is also used in linoleum, mortar,
and adhesives. Mica can be added to rubber products as a
lubricant and mold release agent. It is used as a filler
boosting electrical insulation, heat resistance, and
acid/alkali resistance. Mica is also used to make mica
paper, mica panel, mica ceramics, pearl mica pigments,
and cast mica products.
Uses
Mica
powder is widely used as a raw material in mica
ceramics, a filler in plastic, rubber, building
materials, and paints, as a protective layer on welding
rods, as an additive in drilling mud, and also in
coatings, paints, fire safety products, linoleum, paper,
oil drilling products, and cosmetics.
1. Acts as a sealant when
used as a drilling mud additive.
2. In building surface
materials, it protects against rain, insulates against
the heat or cold, and provides decorative effects.
3. A coating of mica powder
mixed with mineral wool and resin can provide a
decorative layer on concrete, stone, and masonry outer
walls.
4. Used in the protective
layers on welding rods, wires, and cables.
5. Used as a filler in
linoleum, pipe mortar, and adhesive. It can be used to
make decorative coatings and sound-a sorting plaster.
Used as a filler in ceiling panels and concrete and
cement mortar; increases the strength of cement mortar.
6. When used as a filler in
rubber products, mica acts as a lubricant and provides
electrical insulation, heat resistance, and acid/alkali
resistance. It serves as a covering agent in tire
reconditioning, and can provide lubrication between tire
and inner tube. Increases mechanical strength,
toughness, adhesion, and anti-aging and anti-corrosion
properties when used in rubber and plastic.
7. When used in paint, mica
can increase reflectivity and heat resistance, reduce
damage from UV radiation, light, and heat, boost
resistance to acids and alkalis, increase electrical
insulation, and provide a bright and attractive paint
layer. It can also enhance their ability, corrosion
resistance, toughness, and tightness, reduce air
permeability, and prevent spotting and crazing. It
increases resistance to oil and water, and prevents
pigments from settling. It is an important filler in
anti-corrosion coatings. It is used in the coating
applied to the model when casting metal, and is also
used in coatings for electroplating tanks. It helps
remove oil when used as a filler in cosmetics. It is an
additive in anti-freezing and anti-sun paints, and is
mixed with sealing paint-on plaster. It is used in the
powder in dry fire extinguishers.
8. Mica can dramatically
enhance the durability of paint and coatings. It
increases water resistance, enhances adhesion between
the paint and the substrate, boosts paint strength, and
improves appearance.
Mica's characteristics are
explained as follows:
Moisture
resistance
Added sericite powder
can significantly increase the water resistance of
paints and coatings with high waterproofing
requirements.
Experimental
results
Iron red containing
no added sericite was soaked starting after 30 hours.
When 5% sericite powder was added, no change had
occurred after 200 hours. Some processes use a 0.5:1
mixture of zinc oxide and sericite powder; 8% of this
mixture added to paints reduces settling, and can take
the place of some barium sulfate and talc powder. This
filler can significantly increase anti-corrosion
properties without changing abrasion resistance, and can
prevent settling. The use of sericite powder is
recommended in heavy anti-corrosion coatings. A
1:0.25:1.25 mixture of zinc phosphate (aluminum
phosphate), zinc oxide, and sericite powder yields the
best results. Sericite powder used in ordinary paints
and coatings can prevent settling. While some
manufacturers use large quantities of organic bentonite
to improve the settling properties of their paints,
excessive organic bentonite can severely degrade the
tightness of paint surface and reduce water resistance.
On the other hand, too little bentonite will do nothing
to prevent settling. The use of sericite instead of
organic bentonite can prevent settling while also
enhancing water resistance. Sericite is easy to use, and
can be added directly. Unlike organic bentonite, there
is no need to use a pre-gelling agent, so sericite can
simplify manufacturing processes.
Anti-covering
applications
Many types of aluminum powder
paints, including oil tank paints and ordinary floating
aluminum powder paint used for protection and
anti-covering, can only be used for approximately one
year before the surface dulls and begins to craze. The
addition of 5%-8% sericite powder can prevent most
discoloration for three years (color may darken
slightly).
Improving
paint durability
Artificial
aging-resistance tests were performed using building
paint with the same formulation and the same pigment
binder ratio but with or without added sericite powder.
The paint without sericite powder began to discolor
after 250 hours. The paint containing 5% sericite powder
began to discolor after 1,000 hours, but did not release
powder.
Note: The foregoing
experiment using paint with the same formulation and the
same pigment binder ratio clearly showed that building
paint with added sericite powder can dramatically boost
the paint's durability indicators. Sericite powder
possesses extremely strong matting and protective
ability, and can reflect close to 90% of UV radiation.
Sericite powder's ability to protect against UV
radiation is chiefly connected with two factors:
Improved mechanical strength and water resistance: The
addition of ultrafine sericite powder made using the wet
method to paint improves the surface luster and
mechanical properties. In particular, addition of
sericite increases water resistance by a factor of three
or more. This is mainly due to the high aspect ratio of
the laminar sericite crystals. Sericite particles retain
a laminar structure regardless of the fineness of the
powder. The effect of inorganic minerals on the film
strength and covering ability of paint is connected with
the physical shape of the mineral particles.
Effectiveness generally decreases in the following
order: laminar > fibrous > columnar > particulate.
Furthermore, sericite powder contains active hydroxyl
groups that readily tight form molecular bonds with
latex and solvents. The parallel, overlapping
arrangement of the sericite particles forms a tight-knit
multilayer network inside the paint film, which
dramatically increases the paint's impermeability and
mechanical strength. Anti-flex performance,
anti-expansion, elongation: The addition of mica powder
to the engineering plastic PVC almost doubles
deformation temperature, but has no significance effect
on mechanical properties, and slightly increases impact
strength. And because PVC is costly, but mica powder
costs much less than PVC, the addition of mica powder to
PVC also offers economic benefits.
Although the addition of 20%
mica powder to nylon 66 slightly degrades mechanical
properties, it significantly improves product appearance
and enhances banding resistance. Mica powder can
significantly improve the insulating ability of rubber
mats. It can boost the expansion resistance, elongation
rate, and perpendicular tear strength of plastic films
to above normal standards. Plastic greenhouse film
containing mica can withstand a temperature 1-3°C higher
than ordinary film.
Conduction:
Antistatic coatings are usually made by adding
conducting matter such as carbon or metal powder to some
kind of polymer. Antistatic coatings containing carbon
are excellent conductors and are widely used in many
applications, including petroleum and chemicals. On the
other hand such coatings provide poor adhesion and
oil-wetting properties, and are available only in
unattractive colors. Antistatic coatings containing
metal powder are costly, heavy, and prone to surface
oxidation of the metal particles. A new solution
consists of a composite material containing mica powder
and with one or several surface layers of
corrosion-resistant conducting material with stable
chemical properties. This material can offer good
conduction, and is a permanent conductor. Chemical
properties are stable, corrosion resistance is
excellent, and colors can be freely adjusted. Light
colors can be readily achieved. Mica can be mixed with
other pigments to obtain antistatic coatings with
different colors. Density is low, and mica and pigments
are readily dispersed in the polymer material. This type
of paint is convenient to use, and can be used for in
the manufacture of electronics, communications, computer
CPUs, pharmaceuticals, chemicals, and precision
instruments.
Comparison with other conducting materials:
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Item Content
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Conducting fibers
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Conducting mica powder |
Conducting metal
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Carbon black, graphite
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Conducting additives |
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Advantages
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Excellent strength, extremely
low oil absorption, very good conduction,
small amounts needed, low-cost.
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Superior conduction,
low-density, low oil absorption, easy to
control resistance, can be very evenly
dispersed within coating layer, consistent
resistance in coating layer
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Extremely good conduction,
low cost |
Extremely good conduction,
low cost |
Low-cost, good dispersion
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Disadvantages
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Poor control of resistance,
easy to cause hazardous breakdown, poor
dispersion, uneven resistance in coating
layer |
Large amount needed, cost
higher than for fibers |
Inherently dark in color,
cannot be made in light colors, high
density, settles readily, poor dispersion,
poor workability, readily oxidized
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Inherently dark in color,
cannot be made in light colors, large oil
absorption, cannot be made as coatings with
high solid content |
Readily lost from migration,
very short-lasting anti-static effect, lasts
only for around six months, only used for
temporary anti-static applications
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Specifications |
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Chemical analysis |
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SiO2 |
53.0% |
-- |
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Al2O3 |
33.0% |
-- |
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K2O |
5.6% |
-- |
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N2O
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0.3% |
-- |
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MgO |
0.18% |
-- |
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CaO |
0.45% |
-- |
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Fe2O3 |
1.8% |
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PH
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7.5±1
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Loss in ignition |
5.0% |
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Physsical properties |
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Whiteness |
65% |
Min
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Oil absorption |
30~45 |
cc/g |
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Moisture Content |
1.0% |
Max |
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Particle size average |
13~14 |
μm |
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Refractive average) |
1.59~1.616
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Specific gravity |
2.67 |
g/cc |
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Mohs |
2.2~2.4 |
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Appearance
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Light gray powder |
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Dispersibility |
Readily disperse in water |
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Explanation |
1. Hardness is greater than that of talc,
but less than that of silica. Can be produced
continuously; will not damage equipment during ball
grinding.
2. Phosphorescent refraction; can be used to increase
the brightness of aqueous paints.
3. Resistant to scratches and abrasion.
4. Heat resistant, UV resistant; laminar structure
provides good thermal insulation.
5. Good adhesive properties. Laminar structure carries a
strong negative charge; hydrophilic, but will not absorb
water; waterproof and rust resistant. |
The foregoing specifications are provided for reference
only. |
