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Muscovite or Phlogopite? Which mica is best for your application?

June 9, 2020

Of the various varieties of naturally occurring mica, muscovite and phlogopite mica occur most prominently. Muscovite is a hydrated silicate of aluminum and potassium while phlogopite is a magnesium and potassium bearing hydrated silicate. The differing chemical compositions of muscovite and phlogopite mica impact their physical properties and capabilities. Muscovite is ruby, green, or white in color while phlogopite is amber, silver, or green in color.
 
Muscovite:
Muscovite has greater dielectric strength than any other insulating material. Muscovite is widely recognized as the best mica for electronic devices due to its thermal endurance, mechanical strength, moisture resistance, transparency, and perfection of cleavage. It surpasses all mica in toughness, strength and hardness which contributes to its near insensitivity to atmospheric weathering. Muscovite has tremendous electrical properties and chemical resistance which makes it a mainstay in the electrical insulation industry.
 
Phlogopite:
The maximum operating temperature of phlogopite ranges from 800-1000 degrees Celsius. The ability to tolerate extremely high temperatures allows phlogopite to insulate the foundry and steel industry. Phlogopite mica sheet grades are also utilized to provide heat resistant protection, thermal runway, and flame-retardant protection in the transportation sector. Phlogopite is soft which allows it to adapt to many applications across different industries.
 

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 0.2
Breakdown voltage KV/mm 120 – 200
Moisture Absorption Very low Very low
Acid Reaction Affected by hydrofluoric acid Affected by sulphuric acid
Calcining temp °C 700-800 900-1000
Max. operating temp °C 500-600 800-1000
Shear strength MN/m2 220 – 270 1000-1300
Compression strength MN/m2 190 – 285
Permittivity at 15°C (60°F) 6 – 7 5 — 6

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