'Space metals' aid perfection quest

By Jonathan Amos
Science reporter, BBC News

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Gail Iles shows how a "spongy" metal ignites

Gail Iles dips a spatula into a jar and smears its contents across a piece of tissue. "Just wait," she says, "this is cool."

It starts as an isolated twinkle and then rapidly becomes a cascade of flashes as the black powder dries and reacts with air.

Titanium aluminide is one of the materials being assessed

This is raney nickel, a material so riddled with holes they sometimes call it "spongy nickel". It has a colossal surface area. Just one gram of the stuff may have an effective surface of tens of square metres.

It's what makes the powder so reactive, and the perfect candidate for a catalyst.

It is being used to coat the electrodes of hydrogen fuel cells; and being a very common element, nickel is a lot cheaper than the platinum-based coatings that have traditionally been used for the same job.

But Dr Iles, a research fellow with the European Space Agency (Esa), and colleagues would like to improve the nickel's performance.

The quest is part of a project that has the grand acronym of IMPRESS - Intermetallic and Material Processing in Relation with Earth and Space Solidification.

Simply put, IMPRESS is drawing on space science to develop new materials on Earth, not just for use in catalysts but also in the manufacture of turbine blades in jet engines.

"They sound like two completely different areas, but they both employ what are known as 'intermetallics' which are similar to alloys but are different in that they are actually chemical compounds, in the same way that water is a compound," explains the Esa project leader, Dr David Jarvis.

These new metal combos are interesting because they display a range of mechanical and chemical properties that would put them ahead of conventional alloys - but only if their known shortcomings can be overcome.

Small scales

The intermetallic titanium aluminide, for example, is considerably lighter than the alloys used to make current aero-engine blades; and lowering the weight of components should reduce significantly the environmental impact of planes.

"[Titanium aluminide] is easy enough to make but we have a stumbling block which is oxidation at high temperatures," says Dr Iles.

"What happens is that the oxygen starts to creep in at the surface and what this does is form small cracks which can lead to larger cracks in a process we call embrittlement."

The intention is to try to make turbine blades from intermetallics

No-one wants to use components inside a hot engine that are liable to crack.

The scientists hope to find a way around these kinds of problems. A "sprinkling" of impurities such as the elements tantalum and niobium is one answer.

To really understand how such alterations work, though, you need to look very closely - at the scale of individual groups of atoms.

That has brought the project to the European Synchrotron Radiation Facility (ESRF) in Grenoble, France.

This is a giant circular machine that produces an intense, high-energy light (X-rays) that can pierce just about any material, revealing its inner structure at very high resolutions.

A "sister" facility on the same site, the Institut Laue-Langevin (ILL), is providing complementary information.

Big pull

IMPRESS will scrutinise its materials here at various stages of preparation, eventually taking the lessons back into the industrial process.

If you are wondering why Esa is so interested in all of this, it's because the agency has expertise in working in the weightless conditions found in space - and the near absence of gravity (microgravity) has a profound influence on the way molten metals come together to form intermetallics and "standard" alloys.

The ESRF facility is used to probe the very fine structure of materials

With no "up" and "down" in the space environment, a melt doesn't rise and sink as it would at the planet's surface and that means solidification can turn out very differently.

"Gravity induces a lot of segregation of the elements," explains IMPRESS scientist Dr Guillaume Reinhart.

"For instance, tantalum and niobium are heavy atoms and in doing the solidification process on the ground, they will segregate in different places and produce a very heterogeneous material.

"If you do this in microgravity, you obtain a very homogenous material because you prevent separation; and you have a much more efficient material, mechanically."

Smooth blend

IMPRESS is producing small amounts of intermetallics and other materials in weightless conditions.

They are made in a tiny furnace launched on a sounding rocket, or deployed in a "drop tower" or on the parabolic flights of special planes. Just a few seconds or minutes of microgravity are needed to make a model sample.

EUROPEAN LIGHT SOURCE

Electrons are fired into a linac, or straight accelerator. They're boosted in a small ring before entering the storage ring. The superfast particles are corralled by a train of magnets. Energy lost by turning electrons emerges as intense light (X-rays).

The 850m-circumference ring has 32 magnet clusters, or cells. Electrons turned by plain magnets produce 'standard' X-rays. Particles 'wiggled' at undulator magnets emit stronger X-rays. X-rays can't turn with electrons and head straight down beamlines.

Experiment 'hutches' receive the most intense X-rays in Europe. The light probes materials on the atomic and molecular scale. Robots can place many samples in the beam for rapid science. ESRF data leads to new materials, drugs, electronics, etc.

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"The aim is to obtain the perfect material that we can compare with the samples we produce on the ground. We investigate them by performing characterisation with neutrons and X-rays, in order to get a full description of the materials," says Dr Reinhart.

Dr Iles adds: "How these materials form can change entirely the end product and the end properties. How the atoms bond together, how they decide to solidify; how they blend is critical to their performance."

Ultimately, IMPRESS is the type of project that will be pursued in Europe's Columbus science laboratory, recently added to the space station.

A materials science facility, complete with furnace, is likely to be incorporated into Columbus in the near future.

Experiments on the space station have the advantage over sounding rockets and drop towers in that they can last for weeks or even months; and be repeated over and over again. Many samples, and in larger quantities, can be produced.

IMPRESS is funded through the European Commission's Framework Programme. It draws together the academic and industrial expertise of more than 40 research groups across the EU and Russia.

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