Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Extra-large ’atoms’ allow Penn physicists to solve the riddle of why things melt

01.07.2005


Physicists at the University of Pennsylvania have experimentally discovered a fundamental principal about how solid materials melt. Their studies have shown explicitly that melting begins at defects within the crystalline structure of solid matter, beginning along the cracks, grain boundaries and dislocations that are present in the otherwise orderly array of atoms. Their findings, which will appear today in the journal Science, answer longstanding fundamental questions about melting and will likely influence research in physics, chemistry, materials science and engineering, as well as studies of biological importance.

"Melting is one of the most fundamental phenomena in physics and is one of the phase transitions most frequently seen in daily life," said Arjun Yodh, a professor in Penn’s Department of Astronomy and Physics. "Yet major details about the mechanisms that drive the melting of an ice cube are missing. Superficially, the principle is straightforward. As a solid heats up, molecules within the ice acquire more energy and jiggle around more, driving the transition from a solid to a liquid. This is true in part, but reality is richer and more complex."

In the Science paper, the Penn physicists show direct evidence for a leading theory of melting, the notion that the start of melting – premelting – occurs at imperfections in the orderly structure of solid crystals. Premelting occurs in areas where the alignment of atoms is not perfect, especially at the boundaries within crystals where the patterns of atoms shift much like imperfections in the grain of a piece of wood.



One problem with proving theories of how things melt is size; one simply cannot see the atoms in a solid structure as it melts. Not only are the atoms very small, but the solid matter tends to obscure what goes on inside. To get around these problems, Yodh and his Penn colleagues made atoms bigger.

"We created translucent three-dimensional crystals from thermally-responsive colloidal spheres. The spheres are like small beads visible in an optical microscope," said Ahmed Alsayed, a doctoral student in the Department of Astronomy and Physics and lead author of the study. "The spheres swell or collapse significantly with small changes in temperature, and they exhibit other useful properties that allow them to behave like enormous versions of atoms for the purpose of our experiment."

As they raised the temperature of the colloidal particle crystal, the researchers could record changes within the crystal by following the motions of many individual spheres using a microscope and a video recorder.

"When we raised the temperature, we could track the vibrational movement of the spheres," Alsayed said. "Premelting was first revealed as an increased movement along the lines of defects in the crystal. These motions then spread into the more ordered parts of the crystal. We could see that the amount of premelting depended on the type of crystal defect and on the distance from the defect."

The researchers believe these observations will lead to a better understanding of the melting process and enable more quantitative predictions of just how a substance might melt.

"The existence of premelting inside solid materials implies that liquids exist within crystals before their melting temperature is reached," Yodh said. "Understanding this effect will provide insight for the design of strong materials that are more or less impervious to temperature changes and could also apply to our theories of how natural materials, such as water, evolve in our environment."

Other Penn researchers involved in this study are Mohammad Islam, Jian Zhang, and Peter Collings, who is also a professor of physics at Swarthmore College.

Greg Lester | EurekAlert!
Further information:
http://www.upenn.edu

More articles from Physics and Astronomy:

nachricht When fluid flows almost as fast as light -- with quantum rotation
22.06.2018 | The Henryk Niewodniczanski Institute of Nuclear Physics Polish Academy of Sciences

nachricht Thermal Radiation from Tiny Particles
22.06.2018 | Universität Greifswald

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

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

Im Focus: Temperature-controlled fiber-optic light source with liquid core

In a recent publication in the renowned journal Optica, scientists of Leibniz-Institute of Photonic Technology (Leibniz IPHT) in Jena showed that they can accurately control the optical properties of liquid-core fiber lasers and therefore their spectral band width by temperature and pressure tuning.

Already last year, the researchers provided experimental proof of a new dynamic of hybrid solitons– temporally and spectrally stationary light waves resulting...

Im Focus: Overdosing on Calcium

Nano crystals impact stem cell fate during bone formation

Scientists from the University of Freiburg and the University of Basel identified a master regulator for bone regeneration. Prasad Shastri, Professor of...

Im Focus: AchemAsia 2019 will take place in Shanghai

Moving into its fourth decade, AchemAsia is setting out for new horizons: The International Expo and Innovation Forum for Sustainable Chemical Production will take place from 21-23 May 2019 in Shanghai, China. With an updated event profile, the eleventh edition focusses on topics that are especially relevant for the Chinese process industry, putting a strong emphasis on sustainability and innovation.

Founded in 1989 as a spin-off of ACHEMA to cater to the needs of China’s then developing industry, AchemAsia has since grown into a platform where the latest...

Im Focus: First real-time test of Li-Fi utilization for the industrial Internet of Things

The BMBF-funded OWICELLS project was successfully completed with a final presentation at the BMW plant in Munich. The presentation demonstrated a Li-Fi communication with a mobile robot, while the robot carried out usual production processes (welding, moving and testing parts) in a 5x5m² production cell. The robust, optical wireless transmission is based on spatial diversity; in other words, data is sent and received simultaneously by several LEDs and several photodiodes. The system can transmit data at more than 100 Mbit/s and five milliseconds latency.

Modern production technologies in the automobile industry must become more flexible in order to fulfil individual customer requirements.

Im Focus: Sharp images with flexible fibers

An international team of scientists has discovered a new way to transfer image information through multimodal fibers with almost no distortion - even if the fiber is bent. The results of the study, to which scientist from the Leibniz-Institute of Photonic Technology Jena (Leibniz IPHT) contributed, were published on 6thJune in the highly-cited journal Physical Review Letters.

Endoscopes allow doctors to see into a patient’s body like through a keyhole. Typically, the images are transmitted via a bundle of several hundreds of optical...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Munich conference on asteroid detection, tracking and defense

13.06.2018 | Event News

2nd International Baltic Earth Conference in Denmark: “The Baltic Sea region in Transition”

08.06.2018 | Event News

ISEKI_Food 2018: Conference with Holistic View of Food Production

05.06.2018 | Event News

 
Latest News

Graphene assembled film shows higher thermal conductivity than graphite film

22.06.2018 | Materials Sciences

Fast rising bedrock below West Antarctica reveals an extremely fluid Earth mantle

22.06.2018 | Earth Sciences

Zebrafish's near 360 degree UV-vision knocks stripes off Google Street View

22.06.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>