~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The Raelian Movement
for those who are not afraid of the future : http://www.rael.org
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Source: http://www.newscientist.com/article/mg21628882.100-loss-of-attraction-were-running-out-of-magnets.html?full=true
Loss of attraction: We're running out of magnets
- 30 October 2012 by Richard Webb
Magnets help us drive around, call our friends and power the planet, so the fact that supplies are dwindling concerns us all
Editorial: "We will succeed in creating magnetic miracles"
LAURA LEWIS sighs. "We've always had a hard time with magnets," she says. "People think, 'yeah yeah, they're on the refrigerator, big deal'."
Lewis, who develops new magnetic materials at Northeastern University in Boston, knows a different story. Far from just novelty objects on the fridge, or inscrutable shepherds of iron filings in school experiments, permanent magnets - hunks of metal capable of creating their own magnetic field - lie at the heart of much technology that underpins our modern lives.
That includes personal gadgets from smartphones to headphones, which owe their sleek and compact forms to the latest supremely effective magnets. But the influence of magnets extends much further. "Our world runs on energy: cars, turbines, computers, satellites, transportation," says Steve Constantinides of Arnold Magnetic Technologies, a company based in Rochester, New York. "They all need magnets."
And now a crisis is looming. Buoyed by the world's insatiable appetite for energy, an unprecedented boom in demand for the best magnets is underway. Trouble is, we have no idea where those magnets are going to come from. Suddenly Constantinides, Lewis and their ilk are finding people are interested in their work like never before.
It's not easy to make a good magnet. In the 19th century, the classical theory of electromagnetism taught us that magnetic fields arise whenever electric charges are on the move, and that the field of a naturally occurring magnet can be used to set electric charges in motion. That knowledge was enough to put massive lumps of iron, nature's most obvious magnetic material, at the heart of core electrical technologies such as motors, generators and transformers. There they stored energy and converted mechanical work to electrical currents and vice-versa - and continue doing so to this day.
But explaining how a permanent magnet such as iron acquires and retains the ability to produce and respond to magnetic fields required a good dose of 20th-century physics. It all comes down to the doings of atomic electrons within solids. Apply quantum principles and the precepts of Einstein's relativity to these electrons, and you can show that each one behaves something like a tiny bar magnet, the alignment of which, north-south or south-north, depends on the value of the electron's quantum-mechanical spin.
In most materials, there are equal numbers of electrons with the two opposing spin alignments, so there is no overall magnetic effect. But for a few elements such as iron and its close neighbours in the periodic table, cobalt and nickel, the energy of the whole arrangement can be lowered if the atoms' outermost electrons, the ones involved in chemical bonding, line up with the same spin. Firmly lock these electrons into a solid structure in which they can do that, and then apply a magnetic field, and your material will take away its own field for keeps. You have made a permanent magnet.
A magnet, yes, but is it a good one? "I have a list of what makes a good magnet," says Constantinides. "It's kind of a longish list." Modern iron-based or ferrite magnets tick the boxes of cheapness and abundance of their raw materials. They are also relatively strong and peerlessly resistant to corrosion. But they have one overriding disadvantage: a low energy density, which means you need an awful lot of ferrite to create a large magnetic field. "Ferrite magnets are big and clunky and chunky," says Lewis.
That is OK for the hefty machines used in industry and for large-scale power generation, but in this era of pared-down electronics, we need something a little more svelte. But how to make it? The interactions of the myriad electrons and their spins in a solid material are too complex for theorists to second-guess their behaviour with any certainty. So fabricating better magnets has largely depended on the metallurgist's dark arts: mixing up concoctions of promising elements, putting them in magnetic fields and seeing what happens.
This suck-it-and-see approach has often worked. Aluminium-cobalt-nickel or "Alnico" magnets concocted in the 1930s more than doubled the energy density of the best ferrites. But the real breakthroughs came from the 1970s onwards, with the discovery of the magnetic potential of the lanthanide or rare earth elements. These elements are cast adrift in their own row at the bottom of the periodic table, and they have an unusually large number of electrons that can be coaxed into a common spin alignment. Magnets made from a mixture of cobalt and the rare earth element samarium can store more than twice the energy of Alnico magnets.
The undoubted stars of the show, however, are magnets made of the rare earth element neodymium plus iron and boron. By the 1990s, these Neo magnets had come so far that one the size of a fingertip could create a magnetic field several thousand times stronger than that of Earth's iron core. "At room temperature, Neo is the most powerful magnet we know," says Constantinides.
At room temperature. Early Neo magnets had an annoying weakness - thermal jiggling had a habit of disrupting the carefully aligned spins, so they demagnetised and lost power at temperatures higher than 100 °C. But with a bit more tinkering, a ready fix emerged. For a more thermally robust structure, you just replaced a small proportion - just a few per cent - of the neodymium atoms with those of its heavier rare earth cousin, dysprosium.
And so the stage was set for a magnetic revolution. Anywhere magnets were needed to generate the biggest fields with the smallest bulk, Neo marched in: for power steering in cars; for the spindle motors that keep hard discs, CDs and DVDs rotating for reading; to move the diaphragm that converts electrical pulses into audible sound waves in loudspeakers and headphones; to generate the incredibly intense fields used in medical magnetic resonance imaging. By 2010, while cheap-and-cheerful ferrites still dominated sales in terms of weight, in terms of dollars spent, neodymium-based magnets trumped all others by a factor of 2 to 1.
That's when the problems began. "When Neo was invented, the trouble was in a sense it was too good," says William McCallum, a magnetics researcher at Iowa State University. "It drove up demand to the extent that the availability of rare earths was a problem."
Rare earths are not actually rare- they are present in parts per million in Earth's crust - but they are not easy to find. In the past decade, almost all the world's supply has come from mines in China. But China needs the elements to feed its own economic and consumer boom, and has recently begun slapping on hefty export tariffs - just when there is a global surge in demand.
Greedy green
The culprit this time is not personal consumer electronics. "If you look at a computer, we have maybe 50 grams of magnets in each," says McCallum. Over millions of devices, that adds up to a lot. But it is small beer compared with the quantities now being swallowed by green energy technologies. Motors for wind turbines, and for electric cars and bicycles, must be powerful and lightweight - and only Neo magnets give the performance we need. Every motor in an electric car needs about 2 kilograms of the stuff; for a wind turbine capable of producing a megawatt of power, you need about two-thirds of a tonne. Demand for neodymium magnets for wind turbines alone is projected to increase more than sevenfold between 2010 and 2015 (see diagram).
Some of the shortfall may be met thanks to a reopened mine at Mountain Pass in California and new mines in Australia, but there is a big catch. The high operating temperatures in the motors of electric cars, wind turbines or anywhere torque is being generated mean that Neo magnets need that crucial pinch of dysprosium to keep them stable. And dysprosium is just what the US and Australian ores now coming on stream do not have; only the Chinese ones do.
Hence the pressing need for new super magnets. In the US, the Department of Energy is spearheading an initiative to develop them. Dubbed REACT, for "Rare Earth Alternatives in Critical Technologies", 14 separate teams have received a total of $22 million to come up with magnets that use far less of the problematic rare earth elements - or ideally none at all.
Lewis's team is one of them. They are trying to squeeze improved magnetic performance from iron and nickel mixed together. Normally when you bring together these two potentially magnetic elements they subside into a random structure from which it is difficult to coax a preferred spin alignment. An exception is a mineral structure called tetrataenite in which the iron and nickel atoms are organised in tidy layers with a strong preference to align magnetically.
It is very unlikely that the atoms of a solid structure would naturally diffuse into such an ordered configuration over any useful timescale. Indeed, tetrataenite is not the product of earthly processes: the only known natural examples come from a handful of meteorites. "They derive from asteroids that are big, big, big, big, and they have taken a billion years to cool into their structure," says Lewis.
A billion years is just what we don't have. Lewis's work is all about trying to coax iron and nickel atoms into forming this magnetic structure somewhat more briskly, by adding impurities of different elements to induce them to realign in the right way. "We're trying to fool it into thinking it can access the structure in a more stable manner," she says.
It's a tough ask. "Each of the REACT projects is what I refer to as a one, two or three-miracle scenario," says McCallum. "[Lewis] has to get something to form in minutes or hours that has previously taken eons to form. That's her miracle."
His own is getting cerium to play magnetic ball. Although cerium is a rare earth element, it is far and away the most abundant in the Mountain Pass ore - by weight it makes up half of the rare earths there. "That would change the whole economics of rare earth production," says McCallum. But there is a problem. Each cerium atom has a single electron that can be aligned to make something magnetic, but as soon as you stabilise the electron by binding it in a structure with something else, it gives that electron away. Its magnetisation is highly unstable, especially at those critical higher temperatures.
McCallum's work focuses on introducing atoms of elements into the structure that are sufficiently foreign to make the cerium atoms less profligate with their electrons. Even if that succeeds, cerium is never going to make magnets as good as Neo - but then it doesn't have to. "If you look at the difference between rare earth magnets and non-rare earth magnets, there is a tremendous gap," he says. Any magnet made of friendlier materials that sits anywhere in the gap will take some of the heat from neodymium - and above all from dysprosium.
Constantinides has a similar goal. "We don't need to replace Neo," he says. "We need other materials with a complementary price, performance and ability." His company is following two broad approaches. One is to use computational muscle to try out tweaks to existing non-rare-earth magnets such as Alnico. The other is what he describes as a greenfield approach, using complex algorithms to mix up nature's limited library of magnetic elements in different structures and analyse the results for magnetic stardom. "We've had nickel, iron and cobalt for a long time, but the question is how we can combine these elements in a clever way and come up with something really good," he says. He is by no means assured of quick success: "It takes a lot of teraflops."
Everett Carpenter of Virginia Commonwealth University in Richmond and his team, meanwhile, is investigating a more unlikely character: carbon. Graphite and diamond are not known for their magnetic properties, and adding carbon to iron to make steel diminishes the material's magnetic properties. Bind together tiny nanoscale grains containing carbon and other elements, however, and the picture is very different. "We actually get enhanced properties," says Carpenter. "Significantly enhanced." He thinks such magnets might eventually pack enough punch to beat Neo, and at a much cheaper price - the main problem being how to scale them up to anything like the right size.
At the moment neither he nor any of the other projects under the REACT umbrella can claim a breakthrough. So how does Lewis rate her chances? "Oh my god, very small," she says. Given the pull magnets have over our electrically powered lives, though, we should all have our fingers crossed for a miracle. "If we note even a hint that we can make it, it is going to be huge."
Richard Webb is a feature editor at New Scientist
--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
"Ethics" is simply a last-gasp attempt by deist conservatives and
orthodox dogmatics to keep humanity in ignorance and obscurantism,
through the well tried fermentation of fear, the fear of science and
new technologies.
There is nothing glorious about what our ancestors call history,
it is simply a succession of mistakes, intolerances and violations.
On the contrary, let us embrace Science and the new technologies
unfettered, for it is these which will liberate mankind from the
myth of god, and free us from our age old fears, from disease,
death and the sweat of labour.
Rael
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Tell your friends that they can subscribe to this list by sending an email to:
subscribe@rael-science.org
- - -
To unsubscribe, send an email to:
unsubscribe@rael-science.org
- - -
0 ความคิดเห็น:
แสดงความคิดเห็น