Magnetic Composites

June 17, 2016

Magnetic composites are formed from two separate components, the combination of which produces a magnetic field that has enhanced mechanical strength and corrosion resistance over traditional magnetic materials.

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Magnets can levitate trains and allow them to move at extremely high speeds. Elon Musk's Hyperloop technology utlizes magnets in a low-pressure tube to propel a vessel at speeds nearing 700 mph.

Magnetic composites are materials formed from two separate components, or phases, the combination of which produces a magnetic field. These materials can produce enhanced properties, such as mechanical strength and corrosion resistance, over traditional ferromagnetic materials.

Injection-molded Magnets

Injection-molded magnets are formed by dispersing magnetic powders in a bulk phase (generally resin), which allows for complex shapes to be formed for specific applications. Generally injection-molded magnets offer only weak magnetic strength, and have physical properties similar to plastics.

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An example of injection-molded magnets.

Flexible Magnets

Flexible magnets are formed by mixing a high-coercivity (resistance to demagnetization from an external magnetic field) ferromagnetic compound with a plastic binder. The magnets are then extruded in sheets and magnetized with a line of powerful permanent magnets. The permanent magnets are arranged in a stack with alternating poles (N, S, N, …) facing up, impressing the sheet with alternating magnetic poles. These magnets also have weak magnetic strength, but can have a large degree of flexibility depending on the type of binder used.

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An example of a flexible magnet.

Ceramic (Ferrite) Magnets

Ceramic, or ferrite, magnets are formed from a composite of powdered iron oxide and either a barium or strontium carbonate ceramic. These types of magnetic composites are fairly cheap and can be easily mass-produced in a variety of shapes. Ferrite magnets retain the physical properties of ceramics and are therefore quite brittle but are non-corroding.

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An example of ceramic or ferrite magnets.

Alnico Magnets

Alnico magnets are formed by casting or sintering iron, aluminum, nickel, cobalt, and trace elements that serve to enhance the magnet’s properties. Casting these materials allows for higher magnetic strengths and for the creation of more complex shapes. On the other hand, sintering these materials allows for much better mechanical properties. These types of magnets have better physical properties than ferrite magnets, but not as high as a metal’s mechanical properties. Alnico magnets also offer significant corrosion resistance.

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An example of alnico magnets.

Of these four types of magnets, ceramic and flexible magnets are the cheapest to produce, but also offer the weakest magnetic fields. All magnets will become demagnetized once heated above the Curie point temperature and will need to be remagnitized even after it is cooled. Alnico magnets can be used at the highest temperatures (around 1,000ºF) and flexible magnets reach their Curie point at the lowest temperatures (about 280ºF). These values can vary significantly based on the quality of the magnets used.

Magnetic composites allow magnetism to be used for new applications that require complex material shapes and in situations that require enhanced mechanical properties and corrosion resistance. With continued research, magnetic composites can be created with higher Curie temperatures, allowing for more widespread use in high temperature applications.

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