Spot-welds stick sliding metals
Metals stick as they slip if pressed together and pushed.
Two smooth, cold, metal surfaces are like pieces of tacky Sellotape. They form tiny spot welds that have to be broken apart before they can slide over each other. This, claim two physicists in California1, is another reason why metals stick as they slip if they are pressed together and pushed.
Such microscopic causes of friction and wear are increasingly important as the scale of mechanical engineering shrinks to below whats visible. Here, conventional methods of lubrication start to fail.
Budakian and Putterman glued one ball, a fifth of a millimetre across, to the tip of an optical fibre. The other, two-millimetre ball they attached to a platform that they could move precisely.
When the small ball moved, the optical-fibre beam moved with it. Thus, the researchers could accurately measure the balls displacement, and the forces acting on it. From changes in an electrical current flowing between the balls, they also deduced the size of the area of contact between them.
First, the duo measured how hard it was to pull the balls apart vertically. They found that this rupture stress increased as the area of contact got bigger.
They concluded that the metal balls are tacky at nanometre scales: held together for several seconds, narrow bridges of gold form between the two surfaces, which stretch and break as the balls are separated. The force needed to break these necks of gold depends on how thick they are.
Then the researchers looked at horizontal sliding motions. They found that the force needed to initiate a slip was the same as the force needed to rupture a gold neck as the balls were pulled apart vertically. In other words, it seems that tiny strings of gold are created, stretched and snapped as the metal surfaces move over one another.
PHILIP BALL | Nature Science News
Astronomers find unexpected, dust-obscured star formation in distant galaxy
24.03.2017 | University of Massachusetts at Amherst
Gravitational wave kicks monster black hole out of galactic core
24.03.2017 | NASA/Goddard Space Flight Center
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
24.03.2017 | Materials Sciences
24.03.2017 | Physics and Astronomy
24.03.2017 | Physics and Astronomy