What is mica?
Mica is the name given to a group of 37 minerals that are similar in chemical composition. All mica minerals are silicate minerals, which means they all contain silica. Mineralogists refer to micas as sheet silicates because their molecules form in very distinct, sheet-like layers. Micas are relatively light and soft, and the sheets and flakes of mica are thin, flexible and transparent.
Types of mica minerals
There are several varieties of mica minerals, but the primary ones are muscovite, phlogopite and biotite and lepidolite.
Muscovite, or “white mica”, is the most common form of mica and is often used for electrical insulation and as a substitute for glass.
Phlogophite contains 25-30% magnesia and is preferred for use in the manufacture of dynamos and motors as it is more durable than most commercial muscovite.
Biotite, or “black mica”, is 25% iron, which is the reason for its usual black colour. This high concentration or iron lowers its thermal insulation properties. As a result, it is not usually found in commercial electrical applications.
Lepidolite is used in the manufacture of lithium carbonate, lithium metal, lithium medicines and toughened glass.
Properties of mica
The properties of mica sheets include:
- Chemically inert (stable and unreactive);
- Dielectric (does not conduct electricity);
- Hydrophilic (a special affinity for water);
- Platy (resembling plates);
- Resilient; and
- Transparent to opaque.
Two key qualities of mica minerals are that they are heat-resistant and will not conduct electricity. Combined with its flexibility and resilience, these properties make mica the perfect solution for a wide range of industrial and commercial applications.
Mining for mica
Mica and thermal management
Mica is used in a range of electronic products because of its exceptional properties as an insulator and dielectric material. Many such products depend on sound thermal management in order to function reliably and safely while dealing with excess heat, and mica can support an electrostatic field whilst expending minimal heat energy. In fact, mica can be split to a thickness of between 0.025mm to 0.125mm without losing any of its electrical management properties.
Mica has excellent heat-resistant properties and is stable up to 500 °C (932 °F). Phlogopite mica remains stable at even higher temperatures (to 900 °C (1,650 °F)), meaning it is ideal for use in products where stability and electrical properties are required at high temperatures.
Uses of mica
In its rigid form, mica is ideal for product design and manufacture. In fact, the next time you use a hairdryer, microwave or toaster, turn on your TV or put up Christmas decorations, you are likely to be benefiting from mica’s high temperature insulation properties in one form or another.
Many of the consumer appliances that we use every day only work if they have the capacity to reach high temperatures without malfunctioning or risking the safety of the person using them. Mica offers superb thermal, electrical and fire resistance, is highly durable and can withstand rapid heat transfer. As a result, mica is the ideal material to use in such applications.
Sound thermal insulation makes products more energy-efficient, ensuring they can compete effectively in a crowded market while offering consumers consistent and safe product performance.
Mica is used in the manufacture of a huge number of products and materials, including:
- Alloys (lithium from lepidolite);
- Aluminum production;
- Artificial snow;
- Asphalt roofing felts and shingles (protective coating and weather proofing);
- Batteries (lithium from lepidolite);
- Beauty products casting (mica strainer used in producing bronze, brass and aluminium castings);
- Ceiling tiles
- Christmas ornaments (flocking material and glitter effects);
- Concrete block fillers, refractory bricks and gypsum board (reinforcing structures, fire resistance, sound absorption and corrosion protection);
- Condenser plates (mica is covered with silver to make capacitors);
- Explosives (as an absorbant);
- Foundry works, enamels, mastics and adhesives (improves physical properties and reduces cracking);
- Glass (lithium from lepidolite);
- Guided missiles;
- Heating elements (wire is wrapped around the mica in toasters, irons, kettles and hair dryers);
- Insulators (wires, toasters, irons, etc.);
- Lasers (lithium from lepidolite);
- Liquid level indicators (as mica is unaffected by high temperature and pressure, it is ideal for checking boilers for liquid level and steam pressure);
- Microwave windows;
- Ornamental stone;
- Paint (improves physical properties and durability, adhesion and water proofing);
- Pearlescent pigments (provides lustre in paints, lipstick and other materials);
- Plaster (improves acoustic properties);
- Plastics, such as Fluorosint PTFE (improves thermal and dielectric properties, impact strength and heat resistance);
- Rocket propellants (lithium from lepidolite);
- Rubber (prevents adhesion of rubber compound to the mould during vulcanisation);
- Soldering irons;
- Spark plugs;
- Television tubes (mica spacers hold tube elements in position and are insulated from one another and lithium from lepidolite);
- Transistors (heat and electric insulator);
- Welding electrodes, cables and wires (improves dielectric properties and electrical and mechanical strength of protective coatings);
- Welding rods (lithium from lepidolite); and
- Windows (kerosene lamps and furnaces).
Substitutes and alternative sources
Vermiculite, diatomite and perlite are lightweight mineral and rock materials that are similar to mica minerals and can be used in place of them.
A number of manufactured materials can also be used instead of mica in electronic applications, including styrene, polyester, Teflon and Plexiglass. In addition, pager constructed from ground mica can be used in place of sheet mica for thermal insulating applications.
Origin of the word ‘mica’
The word “mica” is derived from the the Latin word “mica”, which means a “crumb”, “morsel” or “grain”. The naming of the mica group of minerals was probably influenced by the word “micare”, which means “to flash, glitter”.