Ferrite

Ferrite is a hard, brittle, dark gray ceramic that is strongly magnetic. Unlike iron, it barely conducts electricity. That combination is valuable: a magnetic core that doesn't conduct won't waste energy on swirling currents inside it, so ferrite cores work well at the high frequencies used in modern power supplies.

The ferrite in power parts is usually manganese-zinc ferrite. It's made much like pottery, from three ingredients:

• Iron oxide, the main one, roughly 70% by weight;
• Manganese, added as manganese oxide;
• Zinc oxide, which tunes the magnetic properties.

The powders are mixed, heated to around 900 °C so they start to react, and milled very fine. A binder is added, and the powder is pressed in molds into the shapes needed: drums, rings and E-shapes. The parts are then sintered at around 1,200 to 1,400 °C with carefully controlled oxygen. The grains fuse into a dense ceramic with a crystal structure called spinel, and the parts shrink noticeably. Some are ground to exact size afterward.

It forms the cores of the inductors and transformers in the TV. Ferrite was invented in Japan in 1930, and the company TDK was founded in 1935 to make it.