hard magnetic materials2

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HARD MAGNETIC MATERIALS

Hard Magnetic Material can be permanently

magnetized by a strong magnetic field. Steel and

special alloys such as Alcomax, Alnico, and

Ticonal, which contain various amounts of

aluminium, nickel, cobalt, and copper, are usedto make permanent magnets.


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The strongest permanent magnets areceramic, made under high pressure and athigh temperature from powders of various

metal oxides.


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Iron is an example of a natural hard magnetic material. Its magnetic

properties are due to its atomic structure. The electrons in the outer orbit of

an iron atom behave as an electric charge and produce a strong magnetic

field. In a magnetized piece of iron millions of individual iron atoms, called a

domain, are aligned in the same direction. The domains have a north and a


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HISTORY ABOUT HARD MAGNETC MATERIALS

It is believed that permanent magnets have been used for

compasses by the Chinese since ~2500BC. However, itwas only in the early twentieth century that high carbonsteels and then tungsten/chromium containing steelsreplaced lodestone as the best available permanentmagnet material.

These magnets were permanent magnets due to thepinning of domain walls by dislocations and inclusions. Themovement of dislocations within a material is often hindered

by the same factors that effect the motion of domain wallsand as a consequence these steels are mechanically veryhard and are the origin of the term hard magnetic. Thesemagnets had an energy product of approximately 8kJm-3


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APPLICATIONS OF HARD MAGNETIC MATERIALS


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Automotive:

Starter motors, Anti-lock braking systems (ABS), Motor drives for

wipers, Injection pumps, Fans and controls for windows, seats

etc, Loudspeakers, Eddy current brakes, Alternators.


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Telecommunications:

Loudspeakers, Microphones, Telephone ringers,

Electro-acoustic pick-ups, Switches and relays.


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Data Processing:

Disc drives and actuators, Stepping motors,

Printers.


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Consumer Electronics:

DC motors for showers, Washing machines, Drills, Low

voltage DC drives for cordless appliances, Loudspeakers

for TV and Audio, TV beam correction and focusingdevice, Compact-disc drives, Home computers, Video


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Electronic and Instrumentation:

Sensors, Contactless switches, NMR spectrometer,

Energy meter disc, Electro-mechanical transducers,

Crossed field tubes, Flux-transfer trip device, Dampers.


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Industrial:

DC motors for magnetic tools, Robotics, Magnetic

separators for extracting metals and ores, Magnetic

bearings, Servo-motor drives, Lifting apparatus, Brakesand clutches, Meters and measuring equipment.


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Astro and Aerospace:

Frictionless bearings, Stepping motors, Couplings,

Instrumentation, Travelling wave tubes, Auto-compass.


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Biosurgical:

Dentures, Orthodontics, Orthopaedics, Wound closures,

Stomach seals, Repulsion collars, Ferromagnetic probes,

Cancer cell separators, Magnetomotive artificial hearts, NMR /

MRI body scanner.

hard magnetic materials2

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