Mischmetal

Mischmetal

Mischmetal (from German: Mischmetall – “mixed metal”) is an alloy of rare-earth elements. It is also called mischmetal, or rare-earth mischmetal. A typical composition includes approximately 55% cerium, 25% lanthanum, and 15-18% neodymium with other rare earth metals following. Its most common use is in the pyrophoric Ferro cerium “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 Ferro cerium. 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 gas 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.

Preparation

Historically, mischmetal was prepared from monazite, an anhydrous phosphate of the light lanthanides and thorium. The ore was cracked by reaction at high temperature with either concentrated sulfuric acid or sodium hydroxide. Thorium was removed by taking advantage of its weaker basicity relative to the trivalent lanthanides, its 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.

As of 2007, the high demand for neodymium has made it profitable to remove all of the heavier lanthanides and neodymium (and sometimes all of the praseodymium as well) from the natural-abundance lanthanide mixture for separate sale and to include only La-Ce-Pr or La-Ce in the most economical forms of mischmetal. The light lanthanides are so similar in their metallurgical properties that any application for which the original composition would have been suitable would be equally well served by these truncated mixtures. The traditional “rare-earth chloride”, as a commodity chemical, was also used to extract the individual rare earths by companies that did not wish to process the ores directly. As of 2007 mischmetal is typically priced at less than 10 USD per kilogram, and the underlying rare-earth chloride mixtures are typically less than 5 USD/kg.

Use

Mischmetal is used in the preparation of virtually all rare-earth elements. This is because such elements are nearly identical in most chemical processes, meaning that ordinary extraction processes do not distinguish them. Highly specialized processes exploit subtle differences in solubility to separate mischmetal into its constituent elements, with each step producing only an incremental change in composition.

(Zinc-aluminum galvanizing) Traces of a cerium and lanthanum mischmetal are sometimes added to the Galfan galvanizing process for steel wire. This is a zinc and 5-10% aluminum coating, with traces of mischmetal.

Description:

Mischmetal is added to nodularisation and offers a number of benefits which include:

• Increased nucleating sites for Graphite precipitation
• Extended effect of the nodularisation treatment
• Nullification of the harmful effects of any trace elements present in the base Iron
• Control of Graphite morphology from vermicular to nodular

Chemical Composition: