Mischmetal
Mischmetal (from German: Mischmetall – "mixed metal") is an alloy of rare earth elements. It is also called cerium mischmetal, rare earth mischmetal or misch metal. A typical composition includes approximately 50% cerium and 25% lanthanum, with small amounts of neodymium and praseodymium. Its most common use is in the ferrocerium "flint" ignition device of many lighters and torches, although an alloy of only rare-earth elements would be too soft to give good sparks. For this purpose, it is blended with iron oxide and magnesium oxide to form a harder material known as ferrocerium. In chemical formulae it is commonly abbreviated as Mm, e.g. MmNi5.
Carl Auer von Welsbach was not only the discoverer of neodymium and praseodymium, and co-discoverer of lutetium, but was also the inventor of the light-mantle (using thorium), and of the rare earth industry. After extracting necessary thorium content from monazite sand, a lot of lanthanides were left over, for which there was no commercial use. He began exploration for applications to which the rare earths might be put. Among his first discoveries/inventions to bear practical fruit was mischmetal.
Historically, mischmetal was prepared from monazite, an anhydrous phosphate of the light lanthanides and thorium. The ore was cracked by reaction at high temperature either with concentrated sulfuric acid, or with sodium hydroxide. Thorium was removed by taking advantage of its weaker basicity relative to the trivalent lanthanides, its daughter radium was precipitated out using entrainment in barium sulfate, and the remaining lanthanides were converted to their chlorides. The resulting "rare earth chloride" (hexahydrate), sometimes known as "lanthanide chloride", was the major commodity chemical of the rare earth industry. By careful heating, preferably with ammonium chloride or in an atmosphere of hydrogen chloride, the hexahydrate could be dehydrated to provide the anhydrous chloride. Electrolysis of the molten anhydrous chloride (admixed with other anhydrous halide to improve the melt behavior) led to the formation of molten mischmetal, which would then be cast into ingots. Any samarium content of the ore tended not to be reduced to the metal, but accumulated in the molten halide, from which it could later be profitably isolated. Monazite-derived mischmetal typically was about 48% cerium, 25% lanthanum, 17% neodymium, and 5% praseodymium, with the balance being the other lanthanides. When bastnäsite started being processed for rare earth content in about 1965, it too was converted to a version of rare earth chloride, and on to mischmetal. This version was higher in lanthanum and lower in neodymium.
...
Wikipedia