If you follow the alternative energy issues (windmills, solar cells, ethanol for fuel, etc) you have very likely encountered discussions about rare earth elements. This posting is designed to provide the reader a little background. Rare earths are used in lights, batteries, motors, lasers, and many other electronic applications. In addition some of them are used as oil refinery catalysts, in metal alloys and glass polishing and coloring applications just to mention a few non-electronic uses. There are 17 rare earth elements on the periodic table. What makes these metals rare is that they are not often found in concentrations that can be profitably mined. According to Wikipedia, one of them “Cerium” is the 25th most abundant element in the Earth’s crust, however they are widely dispersed. China has the best mines in the world it would seem. China sold these elements at prices low enough to shut down most of the other mines in the world.
The magnets that can be made from several of the elements are vastly more powerful that those made from cobalt, the previous best permanent magnet making metal. Two of the rare earths commonly used are Neodymium and Samarium. They are alloyed with other metals to form permanent magnets. These magnets are replacing non-rare earth alloy magnets in electric motor assemblies because of their magnetic field strength. These rare earth alloy magnets can be made smaller to reduce weight and still create high magnetic flux for electric motors. It is said that the magnetic attraction is so powerful that if your finger is between two of these magnets you will likely experience a fractured finger.
Pure Neodymium has a low Curie temperature so it is only magnetic at low temperatures. Above the Curie point it’s parallel alignment of the magnetic field lines become disordered and it loses its magnetism. To overcome this problem, Neodymium is alloyed with boron and iron to make a permanent magnet that can operate up to approximately 300 C. The rare earths are also vulnerable to corrosion. This problem is resolved by plating.
Although Samarium has a higher Curie temperature, it plays a smaller role than Neodymium because it is more expensive and creates a weaker magnetic field. It is commonly alloyed with Cobalt.
The price and geopolitics are playing a role in the use of rare earths. According to a November 16, 2011 NYTimes article, the prices of rare earths are dropping:
International prices for some light rare earths, like cerium and lanthanum, used in the polishing of flat-screen televisions and the refining of oil, respectively, have fallen as much as two-thirds since August and are still dropping. Prices have declined by roughly one-third since then for highly magnetic rare earths, like neodymium, needed for products like smartphones, computers and large wind turbines.
A chart of the price versus time for Neodymium is shown below:
The price for Neodymium appears to be at about $350 per kilogram.
There are some geopolitical ramifications surrounding rare earths: Again from the Times posting:
China mines 94 percent of the rare earth metals in the world. Through 2008, it supplied almost all of the global annual demand outside of China of 50,000 to 55,000 tons. But it cut export quotas to a little more than 30,000 tons last year and again this year and imposed steep export taxes, producing a shortage in the rest of the world.
Together with a two-month Chinese embargo on shipments to Japan during a territorial dispute a year ago, the trade restrictions and shortage resulted in prices outside China reaching as much as 15 times the level within China last winter. That created a big incentive for companies that use rare earths in their products to move factories to China or find alternatives.
The US had some working rare earth working mines before the advent of the Chinese. I have read that one in California is planning to resume production now that the prices have reached a point where working the mine is economical.