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% |
MICA FAQ
Mica is a naturally occurring mineral prized for its unique properties, including its ability to be easily split into thin, flexible, transparent sheets. This characteristic, combined with its heat resistance and electrical insulation capabilities, makes mica indispensable in various industries. From electronics to cosmetics, mica’s versatility is unmatched. Understanding the different types of mica and their specific applications is crucial for maximizing its benefits and minimizing environmental impact. You can see the qualities shine in various applications.
However, ethical concerns surrounding mica mining practices have led to increased scrutiny and a growing demand for sustainable sourcing. This guide aims to provide a comprehensive overview of mica, covering its properties, uses, and the importance of responsible sourcing.
By exploring the diverse applications of mica and promoting sustainable practices, we can ensure its continued use while minimizing its negative impact on the environment and communities involved in its extraction.
Frequently Asked Questions
-
FAQ: What exactly is mica and how is it formed?
Mica is a group of sheet silicate minerals characterized by their perfect basal cleavage, allowing them to be easily split into thin, flexible sheets. Mica forms through metamorphic processes involving the alteration of igneous and sedimentary rocks under high pressure and temperature. These conditions cause the crystallization of mica minerals from silicate-rich fluids. The specific type of mica formed depends on the chemical composition of the original rock and the metamorphic conditions. This process often occurs deep within the Earth's crust. These unique formations give distinct visual effect to many products.
Real Results: Geological surveys show that mica deposits are often found in regions with a history of intense tectonic activity and metamorphism.
Takeaway:
Mica's formation is a result of complex geological processes that give rise to its unique structure and properties. -
FAQ: What are the different types of mica minerals?
There are several types of mica minerals, with muscovite and phlogopite being the most common and commercially important. Muscovite is a potassium aluminum silicate known for its excellent electrical insulation properties and colorless appearance. Phlogopite is a magnesium aluminum silicate characterized by its brown or amber color and higher heat resistance. Other mica types include biotite (iron-rich), lepidolite (lithium-rich), and sericite (fine-grained muscovite). Each type has slightly different properties that make it suitable for specific applications. These differences stem from their varying chemical compositions and crystal structures.
Real Results: Muscovite accounts for approximately 70% of the global mica production, while phlogopite makes up around 20%.
Takeaway:
Different types of mica offer a range of properties, allowing for tailored applications in various industries. -
FAQ: What are the key physical properties of mica?
Mica's key physical properties include perfect basal cleavage, high dielectric strength, thermal stability, and chemical inertness. Its perfect cleavage allows it to be easily split into thin, flexible sheets. Mica's high dielectric strength makes it an excellent electrical insulator. It can withstand high temperatures without degrading, and it resists chemical reactions. These properties, combined with its lightweight nature, make mica a versatile material for various applications. The mineral's hardness ranges from 2.5 to 4 on the Mohs scale.
Real Results: Mica sheets can be as thin as 0.025 mm while still maintaining their structural integrity and insulating properties.
Takeaway:
Mica's unique combination of physical properties makes it a valuable material in numerous industrial applications. -
FAQ: How does mica's cleavage affect its applications?
Mica's perfect basal cleavage, the ability to split into thin, flexible sheets, is crucial for many of its applications. This property allows mica to be used as a thin film in electronics, as a reinforcing agent in paints, and as a shimmering pigment in cosmetics. The thin sheets can conform to various shapes and surfaces, providing insulation, reinforcement, or visual effects. Without this cleavage, mica would be less versatile and less valuable. The cleavage planes are parallel to the base of the crystal structure.
Real Results: In electronics, thin mica sheets are used as insulators in capacitors, allowing for smaller and more efficient devices.
Takeaway:
Mica's cleavage is a defining characteristic that enables its use in a wide range of applications. -
FAQ: What is the chemical composition of different mica types?
The chemical composition of mica varies depending on the type, but all micas are hydrous phyllosilicate minerals. Muscovite has the chemical formula KAl2(AlSi3O10)(F,OH)2, indicating it is a potassium aluminum silicate. Phlogopite is a magnesium aluminum silicate with the formula KMg3(AlSi3O10)(F,OH)2. Biotite contains iron and magnesium, giving it a darker color, with a formula close to K(Mg,Fe)3(Al,Si)4O10(F,OH)2. The presence of different elements influences the properties of each mica type. These variations determine their suitability for different applications.
Real Results: The iron content in biotite can range from 10% to 28%, affecting its magnetic properties and color.
Takeaway:
The chemical composition of mica directly influences its properties and determines its suitability for specific applications.