Page 48 - Curriculum Visions Dynamic Book

(Left) Magnetic ceramics are used in some loudspeakers.
(Below) Ferrite rod aerial from a radio.
move around. The movement of electrons produces an electric current.
Quartz is the most important natural material that has piezoelectric properties. Many synthetic ceramics have also been made with these properties.
Such materials are extremely widely used. Thin disks of a crystal can be made to vibrate extremely accurately. They form the heart of a quartz watch.
Sonar (detecting objects under water) and ultrasonic cleaning (as in a dentist’s plaque-cleaning drill) also use piezoelectric crystals. Even pick-ups on record
players and microphones use such disks. In the home doorbells and gas cooker
igniters work using piezoelectric effects of ceramics.
Magnetic ceramics
Some metal oxides behave just like iron magnets. They are called ferrites. A common
use for ferrites has been as cores in aerials (ferrite rods) for portable radios and in tuning
coils mounted on circuit boards. Most coils are tuned by moving their ferrite rods. Other uses for
ferrites include permanent magnets, loudspeakers, transformers, and recording and playback heads on
camcorders, VCRs, and tape recorders.
If you think that a magnet made out of rock is
strange, then look at a piece of natural lodestone. This naturally magnetic rock (geologists call it magnetite) is a naturally occurring iron oxide. It is not a piece of iron.
Metals other than iron can also be turned into magnetic ceramic materials.
Ferrites are made using iron oxide, nickel-iron oxide, and manganese-iron oxide. The powders are pressed into shape and then fired so that sintering takes place in just the same way as in other ceramics.
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Ceramic magnets