Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Pulsating chemistry

20.06.2003


A shows the catalytic foil in a relatively smooth state, image B shows a state with many folds.
Photo: Fritz-Haber-Institut


Researchers at the Fritz-Haber Institute in Berlin have recently discovered chemical-thermal-mechanical oscillations that show, indirectly, the rate of certain reactions.

The pattern formation of a catalytic surface reaction is influenced by the temperature at which the reaction takes place. If the temperature of the surface is changed, then the course of the chemical processes changes as well. In extreme cases this change can lead to front formation, i.e. patterns, or, for example, to the overheating of the catalysts. Scientists in the research group led by Professors Harm Hinrich Rotermund and Gerhard Ertl at the Fritz-Haber Institute in Berlin have recently begun to study these processes.
In particular, they have investigated more precisely the influence of heat production during catalytic surface reactions between oxygen and carbon monoxide and pattern formations using an ultra-thin platinum catalyst. During the investigation it was established that, like a beating heart, the platinum foil began to pulsate mechanically during the reactions. With mathematical models and computer simulations the scientists were able to show that the elastic deformations of the foil were in fact due to the oscillation of the chemical reaction itself. This effect can now be used to precisely measure the amount of heat created during these chemical reactions (Science, 20 June, 2003).


Initially, the goal of the researchers (G. Ertl, H.H. Rotermund M. Schunack, Jp. Wolff) was merely investigating the influence of the reaction-induced heat on the pattern formation (spiral waves, standing waves, solitons, etc.) in catalytic surface reactions. The heating of a platinum catalyst during the creation of carbon dioxide is hardly measurable under normal conditions. This means working at a constant temperature with very small pressures (on the order of one-millionth of the normal air pressure) of oxygen and carbon monoxide, the experimental gases which are used, and a sample thickness of approximately 1 mm. In order to be able to fully investigate the temperature effects in spite of the difficulties in measuring, an ultra-thin (0.0002 Millimeter) platinum foil was used as the catalyst. The thickness of the foil is crucial because the heat from the reaction can not be conducted away or neutralized by the metal.
The heat pattern of the reaction is observed using a highly sensitive infrared camera. The resulting pictures clearly showed how, during the reaction, the temperature of the ultra-thin foil fluctuated by several degrees Celsius. And, with only a slightly rise in pressure, temperature oscillations of as much as 20 to 30 degrees were observed. The infrared pictures looked surprisingly like the entire foil catalyst was mechanically oscillating and folds were appearing. An explanation finally came with the use of a normal camera: Every three to four seconds the self-supporting foil was drastically deformed. Two pictures of these oscillations are shown in the figure below.

Figure

The underlying reasons for the oscillations remained, however, unclear. The temperature of the thin foil was obviously increased from the heat of the reaction. This rise in temperature then accelerated the reaction, causing the temperature to go up more. At some point it would be expected that no further increase in the temperature would be found because the additional heat from the reaction would equal the heat lost via radiation. What is observed, however, is a sudden and rapid decrease of the temperature, after which the foil becomes once again smooth.

While Prof. I.G. Kevrekidis visited the Fritz-Haber-Institut extensive discussions lead to further investigations of this phenomenon. Additional experiments were carried out in which the foil was not heated through the chemical reaction. Instead, a focused laser beam was used to achieve this purpose. Through this process it was seen that the appearance of the folds in the foil was a direct result of the increase of the foil’s temperature. In order to more fully investigate these mechanical oscillations intensive mathematical simulations were done by two research groups at Princeton University (I. G. Kevrekidis, P. Holmes, J. E. Cisternas). The results of these calculations showed that the oscillations could only appear for a certain restricted set of parameters. For a fixed ratio between the thickness of the foil and its diameter only a small range of reaction parameters like temperature and partial pressure of the gases would produce the observed effects. In other words, the experimenters just had a stroke of luck!

The Princeton modeling revealed a delicate interplay between thermo-chemistry and thermo-mechanics. Transitions from strongly buckled to smooth states of the foil are mainly due to the oscillations of the chemical reaction itself: the creation of large amounts of carbon dioxide leads to the heating and folding of the foil. If the temperature of the catalyst rises, however, more of the carbon monoxide becomes oxidized until it is fully consumed in the immediate surrounding region. Thereafter the production of the carbon dioxide falls off leading to the contraction of the foil. Because of the slow rate of reaction, the lack of carbon monoxide can be replenished by the arrival of additional gas. Therefore, the entire process begins anew.

At the California Institute of Technology (F. Cirak, M. Ortiz) and at Rutgers University (A. M. Cuitiño ) further sophisticated computer calculations on the elastic deformations of an ultra-thin foil were undertaken. The resulting pictures were quite realistic. The fact that the foil folds very irregularly (first occurring when the plate holding the foil experiences a temperature difference of only one degree) is caused by the way in which it was manufactured. The thin foil is stretched over an approximately four-millimeter hole in a platinum holder and attaches itself to the platinum through adhesion alone. Although the foil over the hole is self-supporting, it is not stretched in a uniform manner. This tension works, at first, to stabilize the smooth form of the foil, so that with small temperature increases no folds appear. The computer simulations showed that if the samples were perfectly symmetrical, they would begin to bend with the smallest temperature increases. If the temperature continued to rise the bending would become more extreme, leading finally to a round hump in the sample.

Chemical-mechanical oscillations, although not including heat-coupling through chemical reactions, were first described 130 years ago in the first years of non-linear dynamics by Gabriel Lippmann in the “Annalen der Physik (Annals of Physics).” Then, for the first time, an iron nail in an aqueous oxidizing solution was brought into contact with a drop of mercury resting in a Petri dish, whereupon the mercury drop would begin to pulsate. Because of the resulting heart-shape of the oscillations, the phenomenon came to be called the “Quicksilver Heart.”

The researchers at the Fritz-Haber-Institute have already shown that the mechanical deformation of the catalytic foil can, in principle, also be used for direct measurement of the energy released by a chemical reaction. With a laser they heated a platinum foil just enough that, although no folds appeared, the foil immediately deformed when only one layer of carbon dioxide or oxygen particles reacted with their respective partner. These deformations can be combined with simple optical methods in order to develop ultra-sensitive instruments for the measurement of rates of chemical reactions.

Original Publication:

Fehmi Cirak, Jaime E. Cisternas, Alberto M. Cuitiño, Gerhard Ertl, Philip Holmes, Ioannis G. Kevrekidis, Michael Ortiz, Harm Hinrich Rotermund, Michael Schunack, Janpeter Wolff.

Oscillatory Thermo-Mechanical Instability of an Ultrathin Catalyst Science, 300, 1932-1935, 2003 Published 20th of June

You can find further information here:

Prof. Dr. Harm Hinrich Rotermund
Fritz-Haber-Institut der Max-Planck-Gesellschaft
Faradayweg 4-6, 14195 Berlin (Dahlem) Germany
Tel.: 049-030 - 8413–5129
Fax: 049-030 - 8413-5106
E-Mail: rotermun@fhi-berlin.mpg.de

Prof. Dr. Harm Hinrich Rotermund | EurekAlert!
Further information:
http://w3.rz-berlin.mpg.de/~rotermun

More articles from Life Sciences:

nachricht A new technique isolates neuronal activity during memory consolidation
22.06.2017 | Spanish National Research Council (CSIC)

nachricht CWRU researchers find a chemical solution to shrink digital data storage
22.06.2017 | Case Western Reserve University

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

Im Focus: Optoelectronic Inline Measurement – Accurate to the Nanometer

Germany counts high-precision manufacturing processes among its advantages as a location. It’s not just the aerospace and automotive industries that require almost waste-free, high-precision manufacturing to provide an efficient way of testing the shape and orientation tolerances of products. Since current inline measurement technology not yet provides the required accuracy, the Fraunhofer Institute for Laser Technology ILT is collaborating with four renowned industry partners in the INSPIRE project to develop inline sensors with a new accuracy class. Funded by the German Federal Ministry of Education and Research (BMBF), the project is scheduled to run until the end of 2019.

New Manufacturing Technologies for New Products

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

A new technique isolates neuronal activity during memory consolidation

22.06.2017 | Life Sciences

Plant inspiration could lead to flexible electronics

22.06.2017 | Materials Sciences

A rhodium-based catalyst for making organosilicon using less precious metal

22.06.2017 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>