Cleantech: nickel foams become diesel particulate filters

High-temperature nickel foam. Image courtesy www.incosp.com

Now that nickel foams for batteries have become a mass product for cordless phones and power tools, digital cameras and hybrid car batteries, most production has been relocated to Asia – and researchers in Europe are trying to find new applications.  

But metal foams remain expensive to produce, and while they have been adopted in premium applications such as batteries, the foams cannot compete on price with conventional materials in applications such as auto parts.

At the Materials Research Centre of the École des Mines de Paris, in Evry, south of Paris, a research centre composed of 90 researchers and 65 PhD students, deputy director Yves Bienvenu is convinced there is further potential in metal foams. The École des Mines is part of the ParisTech association of leading scientific and technical institutions.

In collaboration with an industrial partner, INCO (one of the world’s leading nickel producers), IFAM , a Fraunhofer Institute in Dresden, Germany, and the Laboratory of Applied Thermodynamics of Aristotle University in Thessaloniki, Greece, Bienvenu and his team have developed diesel particulate filters.

“If we can filter a liquid, why not a gas and even a hot gas?” asks Bienvenu. The challenge was to optimise the efficiency and durability of the filter in the presence of hot exhaust gases and the associated thermomechanical stresses.

According to Bienvenu, “The current generation of diesel particulate filter made of  silicon carbide or other ceramic materials tend to break after some years. Furthermore, their filter function is limited to the surface of the channels, instead of the complete volume, as in a foam”.

With cars with the new metal foam filters are being road tested in Greece currently, and a pilot-scale factory being built by INCO and Süd Chemie (a specialist in catalysts in Germany), commercialisation is near.

This has left the team at the Materials Research Centre searching for yet more applications and partners. “Porous electrodes for fuel cells and for the high temperature electrolysis of water (for hydrogen production) and also electromagnetic shields may use nickel foams,” says Bienvenu.

He also believes that metal foams based on titanium and platinum will have a range of applications healthcare.

The foams are manufactured by melting metals with a foaming agent that releases gas in a controlled way when heated, forming bubbles in the metal that are retained when the metal cools.

The resulting three-dimensional porous structures can conduct electricity and have extraordinary strength (relative to density) as well as exceptional ductility. “To start with, metallic foams can float,” says Bienvenu to underline that one of the main attractions of the foam is its light weight.