Physical Properties
In general, mischmetal is soft and brittle. However, because rare earths readily oxidize and absorb hydrogen and nitrogen, it is extremely difficult to produce a thoroughly pure sample of mischmetal in order to test it for mechanical and electrical properties. According to Jiangxi Xinji Metals, a leading Chinese manufacturer of mischmetal, even rare earth metals offered to 99.99999% commercial purity may only contain 99.99% rare earth metal in the delivered condition, with up to 10,000 parts per million oxygen impurities in the alloy.
These impurities create lattice defects and microstructural inclusions that negatively impact strength, toughness, ductility and conductivity properties. As a result, no significant and reliable physical property data on the various commercial mischmetals is published by industry or in research literature.
History
Mischmetal was originally called Auer's metal, after Carl Auer von Welsbach who created the alloy from remnant material from his experiments in creating the thorium-powered light-mantle in 1885. His thorium source was monazite sand, of which some 90-95% was composed of other rare earth metals. None of these at the time had commercial value.
By 1903, von Welsbach had optimized the fusion electrolysis procedure to produce a void-free cerium alloy with approximately 30% iron. The iron addition added significant hardness to the cerium, which is a pyrophoric rare earth. He had created Auermetall, now known as ferrocerium, which is the basic material used for flints in fire starters and lighters.
From this discovery, von Welsbach realized that he could separate the various rare earths from a given ore using electrolytic processes. By carefully using the different solubility properties of the various rare earths to his advantage, he could isolate them from their naturally occuring chloride forms. This was the beginning of the rare earth metals industry -- now the various pure elements could be evaluated and used for new commercial applications.
Mischmetal in the Marketplace and Industry
Mischmetal is not traded as a commodity on major exchanges, but is consumed through multiple channels of industry. China is the largest producer in the world, and Molycorp in California sits on the only other known commercially viable bastanite mine in the world, from which mischmetal can be obtained. The alloy is used in the production of all pure rare earth metals and many rare earth alloys.
It is also directly consumed in industrial applications:
- As an oxygen getterer in vacuum tube manufacturing.
- In batteries relying on metal hydride technology.
- As a spark source to start fires and flames, as well as in movie special effects.
- By steel and non-ferrous metals manufacturers to improve castability and mechanical properties in certain alloys.