Ceramic knife
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A ceramic knife is a knife made out of very hard ceramic, often zirconium dioxide. These knives stay sharp longer than steel knives. They are also extremely brittle and will shatter or crack when used to pry. They chip on the edge if used roughly. Usually, though, the edge will merely chip when dropped. Although porcelain is a type of ceramic material, unlike porcelain, ceramic knives do not shatter easily.
Zirconia is very hard, for example it comes in at 11 on the Mohs scale of mineral hardness, compared to 7 to 8 for hardened steel, and 15 for diamond. As such, they cannot be resharpened the same way as steel blades, and will require sharpening with a diamond sharpener at the factory. Ceramic kitchen knives normally come with a complimentary resharpening service.
The company Kyocera also offer a so-called 'black' blade made by an extra firing or sintering in a hot-isostatic press (HIP). These black knives are said to be 'tougher'.
They are used by chefs, Explosive Ordinance Disposal (they are not conductive and not magnetic), divers (they will not rust in salt water), and people with certain allergies (chemically inert).
Ceramic knives present a conceptual problem to the security industry since ceramics are not picked up by metal detectors. To solve this many manufacturers on non-military knives include a quantity of metal in each knife to ensure they are detectable with standard equipment. Ceramic knives can be detected by extremely high frequency scanners, although (as of 2006) these scanners are not yet in widespread use.
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