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  (Source: Supercond. Sci. Tech/Univ. of Cambridge)
New superconducting material could open the door to commercial viability in some applications

A new superconductor made by an international team of researchers from the University of CambridgeFlorida State University (FSU), and the Boeing Comp. (BA) have bumped the record for strongest superconductor to 17.6 Tesla (T), breaking the previous held record by 0.36 T, or roughly 2.1 percent.  While that may not sound like much, it's the first increase in the mark in more than a decade, with the last record (17.24 T) set in 2003.

The new superconductor is about 550,000 times stronger than the Earth's relatively low-density field, about 3,500 times the density of a fridge magnet, and over the twice as strong as the CMS Magnet of the Large Hadron Collider.  Previously, even small bumps have led to new commercialization prospects for superconductors.  And given the well-documented and carefully thought out manufacturing process, this study has given those looking to commercialize a pretty clear roadmap.

I. Superconductors -- The Road to Discovery

Superconductivity is a phase transition that causes electrical resistance to reduce to zero, as the title suggests.  The phase transition occurs due to quantum effects, but there's a catch -- it can only operate in very pure, homogenous materials and in most known superconductors is only observed at very low temperatures.

Most metals react to form oxides and other compounds.  A notable exception is mercury, which behaves somewhat like a noble gas due to its filled electron shell.  As a result, mercury forms weak bonds and is relatively easy to extract in pure elemental form.  When chilled to 4K it starts to superconduct.

To get there you need something to cool to such a low temperature, which required the invention of the refrigeration cycle.  Gases when they are throttled -- allowed to expand in volume in order to reduce pressure -- see an increase in entropy (disorder) and a decrease in temperature, if the throttling is done in a very well-insulated system.  This is the Joule–Thomson effect.  The cooled gas can then be used to cool another substance -- like your food.

The catch is that you have to expand the gas at below a certain temperature -- its so called "inversion temperature" (Ti), where the gas begins to behave ideally.  For any given gas, this temperature is equal to about 27/4th of the critical temperature (TC), the temperature above which liquid and gas coexist at the same density to form a homogeneous single-phase fluid. 

For diatomic nitrogen at standard pressure (N@ 1 atm), Ti = 621 K, or a little more than twice as hot as room temperature (273.14 K).  For diatomic oxygen (O2 @ 1 atm), Ti = 764 K [source].  So at room temperature air -- composed primarily of oxygen and nitrogen -- can be directly compressed and expanded to make it a liquid and provide cooling.

II. Cooler Than Ice

But where things get tricky is helium.  Its inversion temperature is 51 K.  But scientists devised a way around that -- the Hampson–Linde cycle.  The Curious Physicist has a good overview of how this technology works -- but in short the key trick is to just do basically everything you'd do with the standard Siemens cycle except it's all done on a vapor, which is allowed to slowly liquify in one part of the cycle.

The method was first devised independently by not one, but two researchers in 1895 -- German Professor Carl von Linde of Technische Hochschule München (Univ. of Munich) and William Hampson, a UK lawyer turned self-educated scientist and engineer.
JT Cooler
Another diagram of a cooler using the Linde-Hampson cycle [Image Source: Wikimedia Commons]

A little over a decade after Hampson–Linde cycle came on the scene in the lab, they became available to other researchers.  In 1908 a Dutch physics professor by the name of Professor Heike Kamerlingh Onnes began to experiment with the idea of liquifying helium -- which has a super-cold temperature of around 4 K (with the "around" bit being due to isotopal impurity).  Working in his lab at the University of Leiden he quickly succeeded in becoming the first to liquify helium, recording a temperature of around 4.2 K sometime in 1908.

Professor Onnes
Professor Heike Kamerlingh Onnes [Image Source: Wikimedia Commons]

What he would witness two years later, in 1911, was an amazing, if accidental discovery.  Mercury is in liquid form at room temperature, but freezes at ~234 K.  Like all metals the resistance decreases as temperature decreases.  But in 1911 there was still a lively debate among physicists over whether the conductivity reached some non-zero minima at absolute zero temperature -- as the slope of the resistance vs. temperature plot would suggest.  Others believed that the resistance would drop sharply to zero as you approached absolute zero.

The helium cooling provided a perfect means to solidify a sample of supercooled metal mercury in order to find out which hypothesis was correct.  But at 4.2 K something even more remarkable was witnessed -- the sample showed no electrical resistance at all, something no one had predicted.

In his lab notebook he wrote:

Mercury has passed into a new state, which on account of its extraordinary electrical properties may be called the superconductive state.

Recognizing the importance, in 1911 he published his discovery [PDF] (it's a good read -- especially the part where he recognizes a young Albert Einstein's Planck-vibrator theories were key to the phenomena he was witnessing).  In 1913, for the work he was awarded the Noble Prize in physics. His student Professor Willem Hendrik Keesom -- who he groomed as his successor -- was the first to solidify helium in 1926, the same year his mentor passed away.

The liquification of helium and Professor Onnes' pioneering findings were intriguing, but the only immediate discovery was the superconductance of lead in 1913.  These discoveries shed light on one early promise -- magnetic field generation.  Zero resistance is one properties of superconductors that has led to commercialization.  Current passing through a wire loop creates a magnetic field, a kind of a nonpermanent magnet called a solenoid.  

With superconductors you can channel vast amounts of current through the material.  You're only limited by the creation of thermal instabilities that can heat and melt a material.  Hence superconductors are today used in most of the world's most powerful magnets, including the CMS magnet used in the LHC experiment, the world's strongest magnet.

III. Type II Superconductors, High Temperature Superconducting, and Magnetic Field Storage

A discovery in 1933 by Professor Fritz Walther Meissner and another German scientist -- Robert Ochsenfeld -- discovered the so-called "Meissner effect" -- which holds part of the key to a second kind of superconductivity's commercialization and the one that's directly relevant to the University of Cambridge team's new work.

The potential of the Meissner effect was fully understood nearly a decade layer.  In 1941, niobium nitride was found to superconduct at 16 K.  Researchers would later discover that this material differed from the lead and mercury pure metal superconductors in another way; it could store magnetic fields.  The previously discovered superconductors resisted weak magnetic fields.  When they were exposed to a very strong magnetic field, they underwent a phase transition and broke down.

NbN was a little different.  It would resist weak fields, but as the field strength intensified, it formed so-called "magnetic vortices" trapping the field.  This was incredibly important as it meant that superconductors could store magnetic energy on a thin layer non-superconducting phase on their surface.  The only catch was that if you exposed this kind of superconductor to progressively stronger magnetic fields, it would reach a point where eventually superconductivity broke down as it did in lead and mercury.

Soviet physics Professor Alexei Alexeyevich Abrikosov theorized the existence of Type I and Type II superconductors.  Type I were the non-magnetic ones like solid lead or mercury.  Type II were the ones capable of storing moderately strong magnetic fields on their surface, like NbN.  The theory he applied actually predated the discovery of NbN, so the neat part here was that physicists actually predicted the possibility of these substances before they discovered them.

Superconductors began to see commercial applications in the 1960s and 1970s and a number of compounds and elemental metals were found to superconduct.  In 1986 it was discovered that cuprate oxides doped with certain other metals, including rare earth metals, were capable of acting as Type II superconductors at much higher temperatures.  The first such superconductor to be found was cuprate lanthanum barium copper oxide (BCO) La2-xBaxCuO4 which at a Tc of 35 K shattered the previous record of 23 K.

The race was on, and since even higher temperature cuprate oxides in this class have been found.  In a sort of beautiful symmetry the current record holder is actually a mercury derived BCO -- HgBa2Ca2Cu3O8+x.  It superconducts at below 135 K at ambient (standard) pressure, or at 153 K if you crank the pressure up to 150 kilobar (roughly 148,000 times standard pressure).

In 2008 a team claimed to see superconduction at Tc=185.6 K (-125.6 ºF) in (Sn1.0Pb0.5In0.5)Ba4Tm5Cu7O20 under a much lower pressure -- 1.000 to 1.250 kilobars.  However, claims regarding that indium superconductor remain controversial.

While much glory has been awarded in the temperature race as scientists continue to try to find a room temperature superconductor (or at least one capable of superconducting at the temperature of frozen water), others have focused on commercializing the strengths of Type II superconductors -- lossless current transmission, magnetic field generation, and magnetic field storage.

IV. A Superconductive Silver Lining

The Cambridge team focused their efforts on the latter application.  Their formulation uses a slightly different kind of BCO superconductor is made of gadolinium barium copper oxide (GdBCO) doped with bits of AgO2 -- silver oxide.

Like all BCO superconductors, the metal oxides act as a superconducting quantum lattice at low temperatures, with the other compounds (typically barium and rare earth metals) acting as spacers.

The progress of the superconductor was supervised by Cambridge Professor Yun-Hua Shi -- an expert in the field.  Professor David Cardwell led the overall design and testing effort and was the senior author of a paper on the work.  Professor John Durrell -- a Cambridge research associate -- was the first author of the paper.

A whopping total of 8 other researchers also contributed to the study and the paper on it.  Among them were a researcher from Boeing (the company who also cofunded the study) and FSU Professor Eric Hellstrom.  The growth, assembly of the finished superconductor structures, and testing was performed at FSU's National High Field Magnet Laboratory.

Superconductor disc
One of the prepared superconductor alloy discs. [Image Source: Univ. of Cambridge]

To coax their formulation into reaching the record field strength, the team first used an unusually high silver percentage -- 15 percent by weight.  This allows for an increase in so-called "flux-pinning centers" in the material.  Prof. Shi describes:

The development of effective pinning sites in GdBCO has been key to this success.

Samples of the carefully controlled metal mix were grown using top-seeded melt growth, which preserves single grains of metal, capable of storing much stronger fields.  Metal grain crystals were machined into discs 3 mm thick (about one-third as thick as that smartphone you might have in your pocket) and 24 mm in diameter.  Two discs were stacked with measurement equipment in between.

Superconductor stack
The finished steel-reinforced record setting stack [Image Source: Supercond. Sci. Tech./Univ. of Cambridge]

Aside from the extra silver and growth technique the other trick to breaking the record involved heating a stainless steel 304 ring and affixing it around the stack.  That techniqued allowed a reinforcing prestress of 250 megapascals (MPa) (2500 bar, or roughly 2500 times standard pressure).

V. Storing Over 500,000 Times the Earth's Magnetic Field in Two Tiny Metal Discs

The researchers then set out to find how much field the construct could store.  At 28 K the team exposed the samples to a field strength of 16 Tesla.  When the field was shut off one sample managed to retain a field strength of 15.4 T, while the other cracked, leading to it storing a weaker 10 T.

Looking to get a higher storage, they bumped the temperature next down to 17.6 K.  That proved the trick.  At 17.8 Teslas -- almost 560,000 times the Earth's magnetic field strength/flux density -- one of the samples managed to store 17.6 Teslas, after the source field was deactivated.

Superconducting Graph
[Image Source: Supercond. Sci. Tech./Univ. of Cambridge]

The team continued to study that star stack and found it stored 10 T at 55 K and extrapolating from their data that it could potentially continue to store 17.6 T all the way up to 32 K, with careful controls.

The storage was quite long-term.  Even after about an hour it had only dropped to around 17.5 Tesla -- still more than the previous record.  The field strength was steady for that sample, also, at 16 mm using Hall sensors, where as it dropped off sharply in the broken samples.  That indicated that careful growth is necessary not only to ensure an attractive field storage, but also to ensure that the range of the field is sufficient to make it commercially useful.

The sample was remagnetized and cracked at 18 Tesla at 26 K, leading the researchers to conclude that the achieved storage -- 17.6 Tesla was around the maximum possible before the brittle sample was overcome by stresses.

The team suggested that while the stainless steel ring method was likely unable to be improved upon do to the unparalleled yield strength and stiffness of the 304 alloy, that future samples could maybe store more field if they were internally reinforced (the previous record from Professor Masato Murakami of the Shibaura Institute of Technology in Japan had used a somewhat similar 26 mm two-disc stack of YBa2 Cu3O7-X (YBCO) reinforced with carbon fiber.

So there's at least one clear route with the record setting material to reaching even more impressive storage.

VI. The Final Frontier -- Commercial Energy Storage

The study on the work was published [PDF] in the field's most prestigious journal, Superconductor Science and Technology.

Professor Cardwell says of the work:

The fact that this record has stood for so long shows just how demanding this field really is.  There are real potential gains to be had with even small increases in field.

This work could herald the arrival of superconductors in real-world applications.  In order to see bulk superconductors applied for everyday use, we need large grains of superconducting material with the required properties that can be manufactured by relatively standard processes.

This record could not have been achieved without the support of our academic and industrial colleagues and partners.  It was a real team effort, and one which we hope will bring these materials a significant step closer to practical applications.

And what does all this mean?  Well you could induce current from various was -- solar photovoltaics, steam from nuclear energy driving induced current, etc. -- and then use a superconducting magnet to fill the superconducting stack with intense magnetism, which you could then harvest by using the field to induce electrical current later in the day, once you've stopped producing.

In terms of time to market, clearly we're a ways off, given that the team struggled to have the sample survive a handful of magnetization cycles.  But if the reinforcement and growth techniques could be simplified, this could bump superconductors a lot closer to becoming a cheap, reliable form of power storage, hence eliminating the problems from sporadic power generation methods like solar and wind.  For now we're stuck with batteries, but superconductors like this one loom as a bright and promising solution on the horizon.

Edit: A previous version of the piece referred to the superconductor as doped with gold oxide (AuO2).  It's actually doped with silver oxide (AgO2).  The article has been corrected.

Sources: Superconductor Science and Technology [PDF], University of Cambridge [press release]

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So let me see if I have this right...
By CaedenV on 7/3/2014 9:40:39 AM , Rating: 2
The idea is that you could have a generator that literally runs on the magnetic charge as fuel? Is that what I am reading here?

Electronics are not my strong suit, but don't generators have a certain amount of resistance between the magnet and induction coil, and wouldn't something like this kind of storage essentially be impractical to harvest the energy from once charged? Or do I have that entirely wrong?

Still, the ability to have relatively long-lasting and high powered electronic super magnets have plenty of other applications in the medical and manufacturing fields that make this tech pretty amazing.

... on another note; how many kids are going to think that "One Tesla" of magnetic power means enough magnetic power to lift one car...

RE: So let me see if I have this right...
By JasonMick on 7/3/2014 10:05:02 AM , Rating: 4
The idea is that you could have a generator that literally runs on the magnetic charge as fuel? Is that what I am reading here?
"Fuel" typically implies stored chemical energy, but your meaning is correct. A better analogy might be that the magnet and supporting electronics replaces a large battery pack.


For a schematic of how it'd work (in one implementation).

RE: So let me see if I have this right...
By Nightbird321 on 7/3/2014 11:31:38 AM , Rating: 2
Anyone know if as storage this would work more like a capacitor or battery?

By M'n'M on 7/3/2014 11:53:53 AM , Rating: 2
More like a capacitor I'd say. A cap stores energy as a virtue of it's electric field. This uses a magnetic field, like an inductor would. Drawing energy from either would reduce the field's magnitude whereas a battery has a more or less constant voltage as it's energy is depleted.

RE: So let me see if I have this right...
By Murloc on 7/3/2014 2:57:03 PM , Rating: 1
capacitors and inductors are the opposite of each other.

A charged capacitor in open circuit has energy stored in its electric field.
Electric field is generated by the charges placed on the plates. Putting those charges there and thus creating the field requires energy.

A charged inductor in closed circuit has a continously flowing current and energy stored in a magnetic field.
Getting the current to flow to regime level requires energy because the magnetic field has to be generated.

Go read the hydraulic analogy on wikipedia if you aren't practical, it helps.

By EricMartello on 7/4/2014 2:22:45 PM , Rating: 1
capacitors and inductors are the opposite of each other.

The simple explanation is that capacitors resist changes in voltage while inductors resist changes in current.

A charged capacitor in open circuit has energy stored in its electric field.

A charged inductor in closed circuit has a continously flowing current and energy stored in a magnetic field.

The key difference is that when an inductor discharges its stored current, the voltage can be substantially higher than the input voltage that charged the inductor. A capacitor will discharge at about the same voltage that was used to charge it or lower.

Go read the hydraulic analogy on wikipedia if you aren't practical, it helps.

So you basically paraphrased what you read on wikipedia so you could appear smart despite not actually knowing what you're talking about? Good job!

RE: So let me see if I have this right...
By m51 on 7/3/2014 6:10:41 PM , Rating: 2
One of the caveats of storing energy in a magnetic field is the huge mechanical stress it creates. It is in fact the same stress as if you stored the same amount of energy via compressed gas in a pressure tank the size and shape of your solenoid.

The advantage is you can more efficiently recover the stored energy with the magnetic field.

The strength of materials tends to be the limiting factor though for large energy storage systems like this.

RE: So let me see if I have this right...
By AntDX316 on 7/6/2014 5:28:26 AM , Rating: 2
but what is the point of this kind of discovery?

what real world uses will develop from this discovery?

By MrBlastman on 7/7/2014 12:06:07 PM , Rating: 2
It will potentially be a cheap way to store excess power during the day for use at night. That is, once they increase the durability of the compound and it's ability to withstand the structural shock of charging and discharging.

By TheDoc9 on 7/3/2014 10:32:43 AM , Rating: 2
It seems kind of dangerous for that guy to be handling raw mercury with thin nitrile gloves.

RE: hmmm...
By JasonMick on 7/3/2014 10:52:09 AM , Rating: 2
It seems kind of dangerous for that guy to be handling raw mercury with thin nitrile gloves.
Agreed, but then again, according to my father, in the 1950s and 1960s dentists would give children small droplets of mercury to play with in their hands. As young scientists he and his brother all did it.

Of course back then they also marched soldiers into nuclear sites back then.

I think the truth lies somewhere in between the somewhat uninformed, laissez-faire approach to biohazards that was practiced a half decade ago and the hyper-paranoid approach extrapolated and inflated from a greater knowledge base that we have today.

If you show me one more study where they give rats some food chemical like taurine or caffeine and "PROVE" it causes cancer (by giving rats 1,000, even 10,000 times the food grade dose) I'm going to lose it -- people often forget that a good deal of what makes up our bodies is toxic and would kill us in sufficient quantities.

As for playing with mercury with thin gloves -- not a good idea to do regularly, but the skin is a relatively strong barrier. The biggest danger is ingestion, typically via environmental contamination. Skin exposure can be a danger, but generally requires repeated long term exposure (e.g. a mercury-containing alloy in a metal bracelet, perhaps).

RE: hmmm...
By Digimonkey on 7/3/2014 11:43:08 AM , Rating: 2
From my understanding the biggest threat of handling mercury are the vapors and residue. I don't think mercury in it's pure elemental form can penetrate skin at all.

RE: hmmm...
By fic2 on 7/3/2014 1:37:53 PM , Rating: 3
I grew up in the 60's and yeah, played with mercury when a thermometer would "accidentally" break.
Definitely cool stuff.
Didn't have access to thin gloves though.

RE: hmmm...
By Kefner on 7/3/2014 2:55:55 PM , Rating: 2
When I was a kid, I remember a buddy of mine having mercury that we would play with. Literally would dump it in our hands, and watch the little bead roll around in our palm. Nothing wrong with me! (that I know of lol)

RE: hmmm...
By Nexos on 7/4/2014 7:07:20 AM , Rating: 2
Playing with a bit of liquid mercury is quite safe, since the absorbtion through the skin is very low. Even if ingested in liquid form its unlikely to cause systematic toxicity. Just make sure some sand is on hand to handle spills, and dont play with it in a unventilated space.

Mercury compounds though, they are no joke. Wouldnt handle those without full hazmat protection.

Mercury non-conductive?
By HoosierEngineer5 on 7/3/2014 10:10:18 AM , Rating: 2
I never knew that. Quite surprising.

RE: Mercury non-conductive?
By JasonMick on 7/3/2014 10:45:28 AM , Rating: 2
I never knew that. Quite surprising.
No it is, that was a mistake. Fixed.

It does become more conductive as a solid as you decrease the temperature.

The debate was among Lord Kelvin and rival physicists over whether the resistance dips sharply to zero at absolute zero or continues its trend to some non-zero minima. The resistance dropping to zero at well above absolute zero (4.2 K) was a happy surprise.

RE: Mercury non-conductive?
By superflex on 7/3/2014 2:58:29 PM , Rating: 3
Nice article Mick.
Happy 4th.

RE: Mercury non-conductive?
By JasonMick on 7/3/2014 6:14:24 PM , Rating: 2
Thanks, you too!! :)

Something is wrong here
By Concillian on 7/3/2014 3:23:22 PM , Rating: 2
Metal grain crystals were machined into discs 3 mm thick (about 3 times that smartphone you might have in your pocket) and 24 mm in diameter.

I'm not really up on the latest smartphone technology, but I think I'd have heard about 1mm thick phones.

Perhaps these units should be cm? Or what's inside the parens should read about 1/3rd the thickness of the smartphone?

I don't know which is correct, but it's one of the two, as either case would put a phone at about 9-10mm thick, which sounds much closer to reality than than 1mm thick.

RE: Something is wrong here
By Cheesew1z69 on 7/4/2014 11:14:04 AM , Rating: 2
I think I'd have heard about 1mm thick phones.
I don't think so. The iphone is 7.6MM, a 1mm phone would be to thin to hold any battery I would think.

RE: Something is wrong here
By PrinceGaz on 7/4/2014 11:39:20 AM , Rating: 2
A 1mm thick phone would be almost as thin as a credit card (I've just measured mine and they are 0.8mm thick).

By Grimer21 on 7/3/2014 12:31:40 PM , Rating: 2
I wish I could work in a magnetic research field. I think magnets are amazing and have so much untapped potential. Some day we're going to see unimaginably amazing things happening that involve magnets.

RE: Magnets!
By PrinceGaz on 7/4/2014 11:32:00 AM , Rating: 2
Yes, magnets have already been used to create all kinds of innovative creations, like a perpetual-motion motor and generator which can create free electricity. At least that's what the website says, anyway :p

There could be all manner of applications which could be developed from study of subatomic particles and the various forces interacting between them, but most of them are likely to be some way in the future yet (even things like FTL drives are probably somewhere down that route eventually).

For now I doubt a superconducting device is likely to find any domestic application (not until we find higher temperature superconductors, perhaps with a peltier cooler), but nuclear fusion powerstations may well use superconducting magnets.

Some Corrections
By m51 on 7/3/2014 6:00:42 PM , Rating: 2
3mm is about 1/3 the thickness of a typical 9mm thick smart phone, not 3 times.

1 bar is standard pressure. So 2500 bar is 2500 times standard pressure, not 250 times.

By Armageddonite on 7/5/2014 1:26:00 PM , Rating: 2
AgO2 is silver oxide, not gold oxide. Gold is Au.

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