They are characterised by nanostructured surfaces with pores measuring only a few nanometres in diameter. An international research team including Dr Daria Andreeva of Bayreuth University (department of Physical Chemistry II) has successfully developed a heavy-duty and cost-efficient ultrasound procedure for the design and production of such metallic structures.
In this process, metals are treated in an aqueous solution in such a way that cavities of a few nanometres evolve, in precisely defined gaps. For these tailor-made structures, there is already a broad spectrum of innovative applications, including air cleaning, energy storage or medical technology. Particularly promising is the use of porous metals in nanocomposites. These are a new class of composite materials, in which a very fine matrix structure is filled with particles ranging in size up to 20 nanometres.
The new technique utilises a process of bubble formation, which is termed cavitation in physics (derived from lat. "cavus" = "hollow"). In seafaring, this process is feared due to the great damage it can cause to ship propellers and turbines. For at very high rotation speeds, steam bubbles form under water. After a short period under extremely high pressure the bubbles collapse inwardly, thus deforming the metallic surfaces. The process of cavitation can also be generated using ultrasound. Ultrasound is composed of compressional waves with frequencies above the audible range (20 kHz) and generates vacuum bubbles in water and aqueous solutions. Temperatures of several thousand degrees centigrade and extremely high pressures of up to 1000 bar arise when these bubbles implode.
A precise control of this process may lead to a targeted nanostructuring of metals suspended in an aqueous solution – given certain physical and chemical characteristics of the metals. For metals react very differently when exposed to such sonication, as Dr Daria Andreeva together with her colleagues in Golm, Berlin and Minsk has shown. In metals with high reactivity such as zinc, aluminium and magnesium, a matrix structure is gradually formed, stabilised by an oxide coating. This results in porous metals that can for instance be further processed in composite materials. Noble metals such as gold, platinum, silver and palladium however behave differently. On account of their low oxidation tendency, they resist the ultrasound treatment and retain their initial structures and properties.
The fact that different metals react in dramatically different fashion to sonication can be exploited for innovations in materials science. Alloys can be converted in such a way to nanocomposites in which particles of the more stable material are encased in a porous matrix of the less stable metal. Very large surface areas thus arise in very limited space, which allow these nanocomposites to be used as catalysts. They effect particularly fast and efficient chemical reactions.
Together with Dr Daria Andreeva, the researchers Prof Dr Andreas Fery, Dr Nicolas Pazos-Perez and Jana Schäferhans, also of the department of Physical Chemistry II, contributed to the research results. With their colleagues at the Max Planck Institute of Colloids and Interfaces in Golm, the Helmholtz-Zentrum Berlin für Materialien und Energie GmbH and the Belarusian State University in Minsk, they have published their latest results online in the journal "Nanoscale".
Publication:Ekaterina V. Skorb, Dmitri Fix, Dmitry G. Shchukin, Helmuth Möhwald, Dmitry V.
Christian Wißler | Universität Bayreuth
New value added to the ICSD (Inorganic Crystal Structure Database)
27.03.2017 | FIZ Karlsruhe – Leibniz-Institut für Informationsinfrastruktur GmbH
Argon is not the 'dope' for metallic hydrogen
24.03.2017 | Carnegie Institution for Science
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
27.03.2017 | Earth Sciences
27.03.2017 | Life Sciences
27.03.2017 | Life Sciences