SIEMENS

Green products are gaining ground so quickly that materials scientists are sounding the alarm. Permanent magnets for wind turbines are a case in point because they require rare-earth metals, including neodymium, praseodymium, and dysprosium. When these materials are optimally combined, their energy density — the unit of storable magnetic energy — exceeds 400 kilojoules per cubic meter (kJ/m3). That value is so high that magnetic systems, compared to conventional magnetic materials, can be made substantially smaller or significantly more powerful.

The designation “rare earth” is actually somewhat misleading, because several of these metals, such as neodymium, aren’t really rare. They are even more common in the Earth’s crust than lead, for example. The problem is that few sizeable deposits have been discovered.

Many rare earths can be found in Inner Mongolia, Western Australia, Greenland, Canada, and the U.S. But 97 percent of the worldwide production of rare-earth elements is presently concentrated in China. “So we’re facing a resource problem,” warns Dr. Thomas Scheiter, Head of the global technology field for Material Substitution and Recycling at Siemens Corporate Technology (CT).

And such resources are hard to do without. For instance, magnets containing only four percent of the silver-gray heavy metal dysprosium enjoy a level of temperature stability that makes them ideal for use in wind energy systems. But today, dysprosium is found only in low-yield deposits, and alternative deposits probably won’t be developed for another five years or more, making supply bottlenecks almost inevitable.

Other rare earth deposits, however, such as those at the Mountain Pass mine in California, may soon become available. More remote is exploitation of the rare-earth deposits that were discovered in mid-2011 under the Pacific Ocean floor, not far from Hawaii and Tahiti.

Hooked on Rare Earths. The core of the problem is the fact that rare-earth metals are required for many high-tech products, including electric motors, cell phones, laser devices, and LCD television sets. And the introduction of energy-saving light bulbs, whose fluorescent materials also require rare-earth elements, has further increased demand. “The excellent properties of rare-earth elements have led to development of new products, which have boosted the market further,” explains Dr. Ulrich Bast, who is in charge of Technology Innovation at CT in Munich.

Electric motors, for instance, can operate either with two-coil magnets or with one coil and one permanent magnet. Synchronous machines equipped with permanent magnets are a separate class of motors and generators. They can substantially reduce the weight of wind turbines. “Use of conventional materials, such as iron and copper, results in a heavy machine,” says Dr. Gotthard Rieger, who heads Magnetic Materials Development at CT. A much more elegant solution would be to equip the external rotors, which “tap” the rotational energy of such a turbine, with thin neodymium-iron-boron magnets that induce an electrical field in the coils. In conventionally- designed wind energy systems, a massive gear set converts relatively slow rotation into fast rotation, which then generates electric power in the generator. New versions, however, are designed to use permanent magnets based on rare-earth elements to generate power directly from the slow rotation. The advantages are that no gear set is needed, weight is reduced, and less maintenance is required, which is an advantage in offshore applications. Siemens already offers gearless turbines in 3-megawatt and 6-megawatt systems.

What this means is that demand for rare-earth elements will continue to increase. What’s more, China is going to play a steadily expanding role in wind turbines and electric vehicles, so it will consume more of its own resources. Siemens is addressing this challenge in the context of an advanced project. For instance, researchers led by Thomas Scheiter are conducting an analysis of the key materials the company uses and in what quantities. They will then analyze current market data to determine whether there are raw materials whose use should be considered critical with regard to their availability.

If the answer is affirmative, the roughly 200 materials scientists at CT will face the task of developing alternatives. Given the impending shortage of rare-earth elements, the company has launched a project designed to develop new kinds of powerful permanent magnets. Such magnets will have to be produced either without any rare-earth elements or with only very small amounts of them.

“In order to use dysprosium more efficiently than has been done in the past, for example, we are no longer going to distribute it throughout all the material in a magnet,” says Rieger. “Instead, we will create a structure in which this element is concentrated only along the crystallite boundaries within the neodymium-iron-boron part of each magnet.” This can be achieved by applying a thin dysprosium layer on the finished magnet, and then using a heat treatment to diffuse it along the grain boundary into the interior. This approach drastically reduces dysprosium use, while leaving needed properties unchanged or even improving them.

Iron Age. Other concepts are aimed at producing motors that are made entirely without rare-earth elements. Permanent magnets composed of iron oxides with admixtures of other oxides already exist. The problem here, however, is that without special pretreatment these sintered ceramic magnets have, on average, only one tenth of the energy density of magnets made with rare earths, making them unsuitable for many motor and generator applications.

In order to minimize the need for rare-earth elements, a Siemens team is therefore working on an innovative material based on an iron-cobalt compound in which nanometer-size magnetic rods, strung together like a string of pearls, are enclosed in a matrix. “We will be able to use such nanostructures to create an optimized permanent magnet, and eventually to develop an alternative to rare-earth elements,” says Rieger. At Siemens in Munich there is already a laboratory facility for synthetizing and investigating such innovative magnetic materials. But isn’t the new solution a kind of regression to an “iron age”? “In principle, iron is an excellent magnetic material,” says Rieger. But it’s still too soon to tell whether the energy density of this material will eventually rival or even surpass that of rare-earth magnets.

Another possible way of achieving sustainable utilization of rare-earth elements is to recycle these materials from electric motors. But so far there are no practical methods for doing so. Instead, electric motors usually wind up in smelters. “It’s true the material is recycled, but the rare earths get mixed in with the rest and are simply lost,” says Bast. With this in mind, Siemens researchers have begun to develop a process that begins with removal of magnets from motors and comprises several phases of recycling. “In the simplest case you just remove magnets from an old motor and install them in a new one,” explains Bast. But that wouldn’t always work because the magnets usually don’t fit. Efforts are therefore underway to design products from the very start in a way that will make it possible to remove permanent magnets from a motor with relative ease for recycling. For this project, which is supported by the German Ministry of Research, partnerships with institutions and companies are also used to develop processes for selectively concentrating magnetic materials from smelters in slag, and for recovering rare-earth metals from it. Researchers estimate this process will be ready for industrial use in a few years.

Thrifty use of rare-earth elements or their substitution would also benefit the environment. “It’s already clear today that it will be possible to manufacture magnets more sustainably in the future,” asserts Dr. Ute Liepold, Project Manager in the Materials Substitution and Recycling unit at Siemens.

A Natural Solution. Even though rare-earth elements presently have been assigned the highest priority among critical raw materials, other substances are arousing concern as well. “The particularly robust refractory metals are also problematic because of potential delivery bottlenecks,” reports Liepold. These metals include niobium, tungsten, and molybdenum, which are used in X-ray tubes, switches, and other applications that require high heat resistance combined with a certain degree of malleability and conductivity. “There certainly won’t be any across-the-board solution for this problem,” says Liepold. “Instead, we need to take a hard look at whatever alternatives are available for each of these materials.”

Other critical materials include metals such as platinum, palladium, indium, gallium, and germanium. The outlook in terms of supplies of gold, silver, and copper is somewhat less dramatic, although their prices will most likely continue to rise. The prospect of higher prices for many key materials is thus being addressed by Siemens researchers. For example, one project is already focused on using aluminum (which costs about half as much as copper) in place of copper in electric conductors. “About 20 percent of copper can be replaced by aluminum during the first phase,” says Liepold. In another project, which is aimed at obviating the need for silver solder, laser welding is being investigated (see Pictures of the Future, Fall 2008, The Mother of Invention).

Siemens is also conducting research with the objective of producing plastics from sources that are more sustainable than petroleum. Its current focus is on biopolymers that can be produced from oil-containing fruits such as the castor-oil plant.

Siemens is presently using conventional thermoplastic polymers, for instance in special-purpose lamps, for applications in medical technology, and for sorting baskets in automated mail applications. In Liepold’s view, using bioplastics to replace these polymers in the future would be a logical next step. “As a green company we have to pay special attention to the issue of raw materials,” Liepold says.