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Forschungszentrum Jülich - Research in Jülich 3_2012

Research in Jülich 3|201212 T he sample, which is about 3 cm in size, does not look different from any old piece of metal: it is dark grey, hard, smooth, and shiny. Chemical- ly, however, the material is very special, explains Dr. Michael Feuerbacher from the Peter Grünberg Institute: “The struc- ture is highly complex, and the iron and aluminium atoms are situated in clearly defined locations.” Experts call this a complex alloy. Ordinary metal alloys, in contrast, have a very simple structure. In industry, palladium, a rare and therefore very expensive noble metal, is the material of choice for this purpose today. Together with colleagues from the Max Planck Institute for Chemical Phys- ics of Solids in Dresden and LMU Mu- nich, the Jülich researchers tested the promising iron–aluminium compound to find out whether it could be used as an alternative. Both iron and aluminium abound on earth, which is why they are much cheaper than palladium. The scientists were excited when the lab experiments showed that the com- pound performs just as well in the reac- tion as palladium. “And that this was the result of our very first experiment,” says Feuerbacher. The tried and tested palla- dium catalyst underwent countless opti- mization cycles during the last few decades, whereas the aluminium–iron crystal resembles an uncut diamond in comparison. However, a little develop- ment work is likely to make this material as effective or even better than palladi- um. “It’s almost like the alchemist’s dream come true,” says Feuerbacher, “Making gold out of something less valu- able.” IT’S ALL IN THE STRUCTURE The crystal’s trump card is the inter- nal arrangement of aluminium atoms and iron atoms. The conversion from ethyne to ethene exclusively occurs at the iron atoms. However, this works only if they keep a certain distance from each other. If two iron atoms are located too closely together, the reaction overshoots the target: the ethene formed is convert- ed into ethane, which cannot form poly- mer chains. If the distance between the iron atoms is too great, however, there is no reaction at all. “The properties of a material are closely associated with its structure,” explains his colleague Dr. Marc Heggen. “Materials this complex are bound to have interesting properties.” It just turned out once more that this is indeed the case. The iron-aluminium crystal de- veloped at Jülich is perfectly suited as a catalyst – an auxiliary substance – for mediating a certain reaction that is ex- tremely important in industry. TEAR-RESISTANT INNOVATION This reaction converts ethyne, also referred to as acetylene, into ethene (ethylene). These two compounds are very similar. But while countless ethene molecules strung together form polyeth- ylene, the tear-resistant plastic material used for supermarket carrier bags, the presence of ethyne results in a material that tears with even the smallest loads. Industrial-grade ethene, however, always contains small amounts of ethyne, which have to be converted into ethene before being used for any plastic material. What have crystals got to do with plastic bags? Quite a lot actually! A crystal made of iron and aluminium de- veloped at Jülich could help fabricate polyethylene in future – the material used for plastic carrier bags and other packaging. The aluminium–iron crystal with the complex structure can be fabricated from a glowing melt of the two metals.

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