New alloy promises to boost rare earth production while improving energy efficiency of engines

June 3, 2016 by Leo Williams
These are alloyed metals being poured from a furnace into a ladle, to be used to fill molds. Credit: Zachary Sims, ORNL

Researchers at the Department of Energy's Oak Ridge National Laboratory and partners Lawrence Livermore National Laboratory and Wisconsin-based Eck Industries have developed aluminum alloys that are both easier to work with and more heat tolerant than existing products.

What may be more important, however, is that the alloys—which contain cerium—have the potential to jump-start the United States' production of rare earth elements.

ORNL scientists Zach Sims, Michael McGuire and Orlando Rios, along with colleagues from Eck, LLNL and Ames Laboratory in Iowa, discuss the technical and economic possibilities for aluminum-cerium alloys in an article in JOM, a publication of the Minerals, Metals & Materials Society.

The team is working as part of the Critical Materials Institute, an Energy Innovation Hub created by the U.S. Department of Energy (DOE) and managed out of DOE's Advanced Manufacturing Office. Based at Ames, the institute works to increase the availability of rare earth metals and other materials critical for U.S. energy security.

Rare earths are a group of elements critical to electronics, alternative energy and other modern technologies. Modern windmills and hybrid autos, for example, rely on strong permanent magnets made with the neodymium and dysprosium. Yet there is no production occurring in North America at this time.

One problem is that cerium accounts for up to half of the rare earth content of many rare earth ores, including those in the United States, and it has been difficult for rare earth producers to find a market for all of the cerium mined. The United States' most common rare earth ore, in fact, contains three times more cerium than neodymium and 500 times more cerium than dysprosium.

Green sand mold of an aerospace engine head. Molten metal is poured in and allowed to cool. Credit: Zachary Sims, ORNL

Aluminum-cerium alloys promise to boost domestic rare earth mining by increasing the demand and, eventually, the value of cerium.

"We have these rare earths that we need for energy technologies," said Rios, "but when you go to extract rare earths, the majority is cerium and lanthanum, which have limited large-volume uses."

If, for example, the new alloys find a place in internal combustion engines, they could quickly transform cerium from an inconvenient byproduct of rare earth mining to a valuable product in itself.

"The aluminum industry is huge," Rios explained. "A lot of aluminum is used in the auto industry, so even a very small implementation into that market would use an enormous amount of cerium." A 1 percent penetration into the market for aluminum alloys would translate to 3,000 tons of cerium, he added.

Rios said components made with aluminum-cerium alloys offer several advantages over those made from existing aluminum alloys, including low cost, high castability, reduced heat-treatment requirements and exceptional high-temperature stability.

"Most alloys with exceptional properties are more difficult to cast," said David Weiss, vice president for engineering and research and development at Eck Industries, "but the aluminum-cerium system has equivalent casting characteristics to the aluminum-silicon alloys."

Aluminum–cerium–magnesium engine head. Image credit: Carlos Jones, ORNL

The key to the alloys' high-temperature performance is a specific aluminum-cerium compound, or intermetallic, which forms inside the alloys as they are melted and cast. This intermetallic melts only at temperatures above 2,000 degrees Fahrenheit.

That heat tolerance makes aluminum-cerium alloys very attractive for use in internal combustion engines, Rios noted. Tests have shown the new alloys to be stable at 300 degrees Celsius (572 degrees Fahrenheit), a temperature that would cause traditional alloys to begin disintegrating. In addition, the stability of this intermetallic sometimes eliminates the need for heat treatments typically needed for aluminum alloys.

Not only would aluminum-cerium alloys allow engines to increase fuel efficiency directly by running hotter, they may also increase fuel efficiency indirectly, by paving the way for lighter engines that use small aluminum-based components or use aluminum alloys to replace cast iron components such as cylinder blocks, transmission cases and cylinder heads.

The team has already cast prototype aircraft cylinder heads in conventional sand molds. The team also cast a fully functional cylinder head for a fossil fuel-powered electric generator in 3D-printed sand molds. This first-of-a-kind demonstration led to a successful engine test performed at ORNL's National Transportation Research Center. The engine was shown to handle exhaust temperatures of over 600 degrees Celsius.

"Three-dimensional printed molds are typically very hard to fill," said ORNL physicist Zachary Sims, "but aluminum-cerium alloys can completely fill the mold thanks to their exceptional castability."

The were jointly invented by researchers at ORNL and Eck Industries. Colleagues at Eck Industries contributed expertise in aluminum casting, and LLNL researchers analyzed the aluminum-cerium castings using synchrotron source X-ray computed tomography.

ORNL is managed by UT-Battelle for the Department of Energy's Office of Science, the single largest supporter of basic research in the physical sciences in the United States. DOE's Office of Science is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

Explore further: Scientists create cheaper magnetic material for cars, wind turbines

More information: Zachary C. Sims et al. Cerium-Based, Intermetallic-Strengthened Aluminum Casting Alloy: High-Volume Co-product Development, JOM (2016). DOI: 10.1007/s11837-016-1943-9

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19 comments

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Eikka
3 / 5 (2) Jun 03, 2016
So why hasn't it been done before?

Turns out it's kind of tricky to make the alloy, because it requires extremely high pressures.

http://www.pnas.o...6/8/2515

Applying 15 GPa or 2.18 million PSI of pressure allows the cerium and aluminium to combine.
gculpex
5 / 5 (3) Jun 03, 2016
So why hasn't it been done before?

Turns out it's kind of tricky to make the alloy, because it requires extremely high pressures.

http://www.pnas.o...6/8/2515

Applying 15 GPa or 2.18 million PSI of pressure allows the cerium and aluminium to combine.


The team has already cast prototype aircraft cylinder heads in conventional sand molds. The team also cast a fully functional cylinder head for a fossil fuel-powered electric generator in 3D-printed sand molds. This first-of-a-kind demonstration led to a successful engine test performed at ORNL's National Transportation Research Center. The engine was shown to handle exhaust temperatures of over 600 degrees Celsius.

no high pressure needed....
IronhorseA
3.7 / 5 (3) Jun 03, 2016
"and it has been difficult for rare earth producers to find a market for all of the cerium mined"
So warehouse it until there is a use for it, and add the storage cost onto the rare earth metals that you're actually using.
Da Schneib
5 / 5 (7) Jun 04, 2016
So why hasn't it been done before?

Turns out it's kind of tricky to make the alloy, because it requires extremely high pressures.
...
Applying 15 GPa or 2.18 million PSI of pressure allows the cerium and aluminium to combine.
Errr, I don't see any mention of this pressure being required anywhere to do with intermetallic cerium aluminum alloys. It's required for a substitutional alloy of Al and Ce, because Ce atoms are far larger than Al atoms; the pressure makes their sizes close enough to make a substitutional alloy out of them, rather than an interstitial alloy.

Your paper has processing being done at 300K; that's 25C, or 77F. These guys are *melting* the alloy at like 2000F. They're *casting it in sand molds*, dude.

None of the people listed as authors of the paper you linked have anything to do with this project at ORNL as far as I can see.

I'm calling BS.
Eikka
3.7 / 5 (3) Jun 04, 2016
I'm calling BS.


Alright, so it's back to the original question: why hasn't this been done before?

They've put all sorts of stuff into aluminium, and someone's got to have tried adding cerium, so why just now? What's the problem with it?
ab3a
3 / 5 (2) Jun 04, 2016
Most aircraft engine cylinders are made of nitrided steel. They can operate at temperatures of as much as 400 C, though the cylinder longevity won't be as good at that temperature.

Normally aircraft engines are run at cylinder head temperatures of about 325 to 350 C. 300 is a bit low. At that temperature, the lead scavenging agents in aircraft gasoline are not that effective.

There is a push toward newer lead-free aviation fuels. Unfortunately, Tetra-Ethyl-Lead is very hard to beat as an octane booster, and the piston engines used in aircraft often run right at the edge of detonation limits. Perhaps with lower power engines using lead free gasoline, these alloys may make sense. However it will take a lot of testing to get them certified for production use.

ab3a
1 / 5 (1) Jun 04, 2016
Most aircraft engine cylinders are made of nitrided steel. They can operate at temperatures of as much as 400 C, though the cylinder longevity won't be as good at that temperature.

Normally aircraft engines are run at cylinder head temperatures of about 325 to 350 C. 300 is a bit low. At that temperature, the lead scavenging agents in aircraft gasoline are not that effective.

There is a push toward newer lead-free aviation fuels. Unfortunately, Tetra-Ethyl-Lead is very hard to beat as an octane booster, and the piston engines used in aircraft often run right at the edge of detonation limits. Perhaps with lower power engines using lead free gasoline, these alloys may make sense. However it will take a lot of testing to get them certified for production use.

Eikka
4 / 5 (2) Jun 04, 2016
Unfortunately, Tetra-Ethyl-Lead is very hard to beat as an octane booster,


It isn't. TEL actually only boosts octane by a small amount, turning marginal low quality fuel into usable fuel. Other additives such as ETBE have a much greater effect.

The main reason why it's sill in use is legislative paralysis. Unleaded avgas is available and there's almost three decades of experience in using it. The other reason is that there are still some engines with soft valve seats in use that would fail without the lead, and so leaded avgas has to be kept available as a "safety" measure so people wouldn't need to fit valve seat inserts.

Most small planes run perfectly well on 91/96UL which is unleaded. Older planes that were designed to run on the now-depreciated 80/87 actually don't run so reliably on the leaded 100LL because it ends up fouling the spark plugs, and they would run better on the unleaded avgas.
Eikka
5 / 5 (1) Jun 04, 2016
https://en.wikipe...ki/Avgas

In 1991, Hjelmco Oil introduced unleaded avgas 91/96UL (also meeting leaded grade 91/98 standard ASTM D910 with the exception of transparent colour) and no lead[citation needed] in Sweden. Engine manufacturers Teledyne Continental Motors, Textron Lycoming, Rotax, and radial engine manufacturer Kalisz have cleared the Hjelmco avgas 91/96UL which in practice means that the fuel can be used in more than 90% of the piston aircraft fleet worldwide.


TEL in avgas is practically displaced already, except for a number of historical planes and other antiques. 100LL is used because it hasn't been banned yet.

The FAA found Swift Fuel to have a motor octane number of 104.4, 96.3% of the energy per unit of mass, and 113% of the energy per unit of volume as 100LL, and meets most of the ASTM D910 standard for leaded aviation fuel. Following tests in two Lycoming engines, the FAA concluded it performs better than 100LL in detonation testing
Eikka
5 / 5 (1) Jun 04, 2016
Most of the quibble about unleaded aviation fuel is about small percentage point differences in performance such as energy density - not really of the octane and detonation performance - or of slightly higher price, which would presumably end up losing the industry billions across the entire fleet.

Thing is, the problems from spraying lead into the environment are many times more expensive to deal with in terms of public health and sanitation.
Da Schneib
5 / 5 (3) Jun 04, 2016
I'm calling BS.


Alright, so it's back to the original question: why hasn't this been done before?

They've put all sorts of stuff into aluminium, and someone's got to have tried adding cerium, so why just now? What's the problem with it?
Actually I'm not as sure as you seem to be that it's been tried. I did a lot of poking around and didn't find much material on Al-Ce alloys; the article is paywalled so there's no way to look at their exact processing. Maybe someone will show up who knows more than we do.
Captain Stumpy
3 / 5 (4) Jun 04, 2016
the article is paywalled so there's no way to look at their exact processing
know of anyone with access to the journal?

the authors list has a contact e-mail to Orlando Rios - though considering the .gov extension it is far more likely you would have better chances getting information from talking to a random passing vehicle on I-5

fmfbrestel
5 / 5 (1) Jun 04, 2016
"and it has been difficult for rare earth producers to find a market for all of the cerium mined"
So warehouse it until there is a use for it, and add the storage cost onto the rare earth metals that you're actually using.


more specifically
add the storage cost onto


The reason there are no rare-earth mines in NA is that they are too expensive to operate at a profit. The Chinese mines have a tough to beat combination of cheap labor PLUS unique geology allowing for much cheaper production. You cant just add more cost to an already unprofitable activity.

You know, unless you want to nationalize the mines and run them at a loss subsidized with tax dollars.
ab3a
1 / 5 (1) Jun 04, 2016
The point of my post was mostly about temperature of operation. Cylinder head temperatures of 350 C are routine in aircraft engines. An alloy that can only handle 300 degrees means that the engine will have to retuned to run at lower power output levels. Thus any savings in weight from using this alloy will be negated by the lower power output.

--and don't forget to leave a margin for the engine to run hotter in case the timing or heat dissipation isn't everything one would expect.
KBK
1 / 5 (2) Jun 05, 2016

The reason there are no rare-earth mines in NA is that they are too expensive to operate at a profit. The Chinese mines have a tough to beat combination of cheap labor PLUS unique geology allowing for much cheaper production. You cant just add more cost to an already unprofitable activity.

You know, unless you want to nationalize the mines and run them at a loss subsidized with tax dollars.


Even with their low labour costs, that is basically what the Chinese are doing.

Our problem is that it takes an average minimum of 2+ years to re-open a mothballed rare earth mine in north america

Which we have plenty of.

So, if we ever get into a situation of not being able to get any tungsten from China, for example, we're screwed.

The US defense industry, space industry, and military, etc... is very uncomfortable with this situation.
24volts
3 / 5 (4) Jun 05, 2016
They might have casted airplane cylinder heads but small engines for various yard tools and generators... would be a much bigger market.

I guess I'm going to have to rebuild my home aluminum smelting setup if this stuff get's popular. 2000 degrees F is about 800 degrees f higher temp than what the regular aluminum alloys I normally smelt and cast need to melt at.
Da Schneib
5 / 5 (1) Jun 05, 2016
@24V, if you intend to do this you should probably invest forty bucks in the paper. They probably discuss methods in there, and I suspect they might be a bit complicated. I'd love to see you accomplish this and hear about the results!
24volts
5 / 5 (1) Jun 20, 2016
@24V, if you intend to do this you should probably invest forty bucks in the paper. They probably discuss methods in there, and I suspect they might be a bit complicated. I'd love to see you accomplish this and hear about the results!


I would love to if I had the money but I don't. If it gets used though I'll start seeing info about it in the casting forums. Then I will find out how it has to be handled.
Captain Stumpy
5 / 5 (1) Jul 07, 2016
I would love to if I had the money but I don't
@24
try crowdfunding... it should be relatively easy to come up with the cost that way
If it gets used though I'll start seeing info about it in the casting forums. Then I will find out how it has to be handled.
true enough
is there a guild in your area you can query?

while you are at it, check out some of the other smithies, small engine shops, jewelry or etc...
they typically use similar smelting and metal forming techniques and if this is utilising a rare earth metal you may pick up interesting testable techniques from the others that will help you

then there is also aircraft manufacturing plants in your area- if there are any, you can query either their safety inspector or similar Tool Shop or Foundry workers ... they may know more about it

what are you smelting at home?
is it self-employed?
Would love to know more about your set-up - considering building a forge out here for steel, etc

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