MICA
WHAT IS MICA?
Mica is a naturally occurring material that belongs to a group of silicate minerals composed of varying amounts of aluminum, potassium, magnesium, iron, and water. It has a thin, sheet-like or plate-like structure with diverse compositions and physical characteristics.
All types form flat, six-sided monoclinic crystals with remarkable cleavage along large surfaces, allowing them to be easily split into optically flat films. When divided into thin layers, they remain tough and elastic, even at high temperatures.
It possesses an exceptional combination of chemical, physical, electrical, thermal, and mechanical properties that are unmatched by any other insulating material.
As a biaxial birefringent crystal, its average refractive index in the visible spectrum is around 1.6. Due to this birefringence, it can introduce a phase delay between two orthogonal components of linear polarization, making it suitable for use as a retardation device.
TYPES OF MICA
MUSCOVITE MICA
KAl2(AlSi3O10)(OH)2
Properties:
- Superior Dielectric Strength: Exceptional electrical insulation capabilities
- Temperature Resistance: Stable performance up to 600°C
- Chemical Stability: Excellent resistance to acids and alkalis
- Mechanical Durability: Outstanding tensile and compressive strength
Applications:
- Electrical insulation components
- Electronics manufacturing
- Motor and generator parts
- Capacitor elements
- Low-voltage switchgear
There are two types of mica, muscovite and phlogopite. The type of mica used is determined by your application and temperature requirement.
Muscovite mica is the most commonly used type of mica in electrical insulation, as it has the best electrical properties among all mica varieties. High-quality samples cleave most easily into the thinnest sheets and show the fewest imperfections, even at atomic or near-atomic scale under AFM or TEM instrumentation. Muscovite mica is commonly divided into two color groups:
- Ruby Muscovite: varies in color from clear to pink to red/brown.
- Green Muscovite: varies in color from pale green to olive to dark green.
Both ruby and green mica have excellent cleavage capabilities permitting it to be split into the thinnest desired film without risk of cracking. Use is a matter of preference and application.
Muscovite mica is harder than phlogopite mica, making it ideal for use in electrical and electronic devices.
Phlogopite mica is a hydrous potassium magnesium aluminium silicate. The calcination temperature reached is about 800°C. Phlogopite mica has superior thermal characteristics, providing essential solutions for high temperature applications.
It is commonly called amber mica and varies in color from light silver to dark brown.
Phlogopite mica is softer than muscovite mica, making it suitable for the manufacture of commutator Micanite; used in commutators of flush running designs. When compared to muscovite mica, it has poor electrical properties and chemical resistance.
PHLOGOPITE MICA
KMg3(AlSi3O10)(OH)2
Properties:
- Superior Dielectric Strength: Exceptional electrical insulation capabilities
- Temperature Resistance: Stable performance up to 600°C
- Chemical Stability: Excellent resistance to acids and alkalis
- Mechanical Durability: Outstanding tensile and compressive strength
Applications:
- Electrical insulation components
- Electronics manufacturing
- Motor and generator parts
- Capacitor elements
- Low-voltage switchgear
PHLOGOPITE MICA
KMg3(AlSi3O10)(OH)2
Properties:
- Superior Dielectric Strength: Exceptional electrical insulation capabilities
- Temperature Resistance: Stable performance up to 600°C
- Chemical Stability: Excellent resistance to acids and alkalis
- Mechanical Durability: Outstanding tensile and compressive strength
Applications:
- Electrical insulation components
- Electronics manufacturing
- Motor and generator parts
- Capacitor elements
- Low-voltage switchgear
Phlogopite mica is a hydrous potassium magnesium aluminium silicate. The calcination temperature reached is about 800°C. Phlogopite mica has superior thermal characteristics, providing essential solutions for high temperature applications.
It is commonly called amber mica and varies in color from light silver to dark brown.
Phlogopite mica is softer than muscovite mica, making it suitable for the manufacture of commutator Micanite; used in commutators of flush running designs. When compared to muscovite mica, it has poor electrical properties and chemical resistance.
COMPARING MUSCOVITE MICA AND PHLOGOPITE MICA
| Properties | Units | Muscovite | Phlogopite |
|---|---|---|---|
| Color | Ruby/ Green/ White | Amber/ Silver/Green | |
| Density | gm/cm3 | 2.6 – 3.2 | 2.6 – 3.2 |
| Specific heat | 0.21 | 0.20 | |
| Hardness | Moh scale | 2.8 – 3.2 | 2.3 – 3.0 |
| Shore Test | 80-105 | 70-100 | |
| Breakdown voltage | KV/mm | 120 – 200 | – |
| Coefficient of expansion per °C perpendicular to cleavage plane | 9 x 10-6 – 36 x 10-6 | 30 x 10-6 – 60 x 10-6 | |
| Thermal conductivity perpendicular to cleavage plane | Gm.cal/sec/cm2/°C/cm | about 0.0013 | about 0.0010 |
| BTU/hr/ft2/0f/ft | about 0.31 | about 0.24 | |
| Thermal conductivity parallel to cleavage plane | Gm.cal/sec/cm2/°C/cm | about 0.012 | |
| BTU/hr/ft2/0f/ft | about 3.0 | ||
| Water of Constitution % | 4.5 | 3.0 | |
| Moisture Absorption | Very low | Very low | |
| Volume Resistivity | 25°C (77°F) ohm cm | 40 x 1013 -2 x 1017 | 1 x 1012 -1 x 1012 |
| Acid Reaction | affected by hydrofluoric acid | affected by sulphuric acid | |
| Insulation resistence | x1013ohm/cm | 4-20000 | 0.1 – 10 |
| Calcining temp | °C | 700-800 | 900-1000 |
| Max. operating temp | °C | 500-600 | 800-1000 |
| Optic axial angle | degrees | 55 – 75 | 5 -25 |
| Tensile strength | MN/m2 | 175 | 1000 |
| Shear strength | MN/m2 | 220 – 270 | 1000-1300 |
| Compression strength | MN/m2 | 190 – 285 | – |
| Modulus of Elasticity | Kgfcm2 x 10-3 lbf/in2 x 10-6 | 1400 – 2100 20 – 30 | 1400 – 2100 20 – 30 |
| Loss tangent | x10-4 | 1-4 | 10-50 |
| Permittivity at 15°C (60°F) | 6 – 7 | 5 -6 |
PHYSICAL PROPERTIES
| Specific gravity | 2.82 |
| Index of refraction | 1.58 |
| Hardness (Moh’s scale) | 2.5 |
| pH value (BS 3483) | 7.7 |
| pH for distilled water | 5.2 |
| Oil Absorbtion | 60-90 g/oil |
| (BS 3483) | 100g Mica |
| Water Soluble | Not more |
| (BS 1765) | than 0.5% |
| Effect by common acids | Slight |
| Phericity Factor | 0.01 |
| Softening point | 2800°F |
CHEMICAL COMPOSITION
| Silica (SiO2 ) | 45.70% |
| Alumina (Al2 O3 ) | 33.10 |
| Potassium Oxide (k2O) | 09.87% |
| Ferric Oxide (Fe2O3) | 02.48% |
| Sodium Oxide (Na2O) | 00.62% |
| Titanium Oxide (TiO2) | Trace |
| Calcium Oxide (CaO) | 00.21% |
| Magnesia (MgO) | 00.38% |
| Moisture @ 100 °C | 00.25% |
| Phosphorous (P) | 00.03% |
| Sulphur (S) | 00.01% |
| Graphitic Carbon (C) | 00.44% |
| Loss on ignition (H2O) | 02.74% |