in movies, when there is a battle between soldiers and blades, there are always all kinds of special effects of electric fire. But if you shoot with an ordinary sword, it's hard to get such a cool spark effect.

to get a spark, you need a special metal-- a mixed rare earth alloy (Mischmetal), to be exact. This is a mixture of a variety of rare earth metals, and it is difficult to quantify its chemical composition, but roughly the most important element is cerium, which accounts for about half of the total, and contains about 25% lanthanum. And a smaller proportion of neodymium and praseodymium.

this alloy is easy to produce bright and hot sparks when quickly scraped with something such as a knife. This is mainly related to cerium, which reacts easily with oxygen in the air. If it is a large piece of metal cerium or alloy, the oxide film formed on the surface will hinder the oxidation reaction, while the scraped fine metal fragments will quickly react with oxygen and exothermic, resulting in bright sparks.

because of this property, rare earth alloys are used to make ignition devices in places such as lighters, as well as film special effects. But the alloy itself was so soft that in 1903 chemist Carl Auer von Welsba added iron to it to produce a more suitable Ferrocerium.

(sparks from lighters, high-speed photography. Slow Mo Lab)

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Natural rare earth elements are often associated with each other, and people begin to understand rare earths from the state of the mixture and separate them one by one. Now rare earth metals are far from being as simple as ignition tools, they have important uses in many fields. For example, neodymium magnets with strong magnetism, the famous high-temperature superconductors (high temperatures are relative, meaning that cooling with liquid nitrogen is enough, at least not with colder liquid helium) yttrium barium copper oxide, all of which are inseparable from rare earth elements.

many of the sound and visual effects of movies are actually exaggerated and do not match the reality, but they do provide a very cool experience for the audience, so they have been used all the time. The sound effects of movies also have many tricks, such as using coconut shells to imitate the sound of horseshoes, adding the sound of crushing walnuts where they are beaten, and so on, which are actually quite interesting. Source: Andres Tretiakov

Source: Chemistry in Pictures