Researchers based at Nagoya University discover ceramic material that contracts on heating by more than twice the previous record-holding material
Machines and devices used in modern industry are required to withstand harsh conditions. When the environmental temperature changes, the volume of the materials used to make these devices usually changes slightly, typically by less than 0.01%. Although this may seem like a trivial change, over time this thermal expansion can seriously degrade the performance of industrial systems and equipment.
A layered ruthenate Ca2RuO4-y ceramic body contracts on heating, or exhibits negative thermal expansion (NTE). The sintered-body structure shows colossal NTE when extremely anisotropic thermal expansion of the crystal grains produces deformation, consuming open spaces (voids) on heating. The total volume change related to NTE reaches 6.7 percent at most, the largest reported so far.
Credit: Koshi Takenaka
Materials that contract on heating, or negative thermal expansion materials, are therefore of great interest to industrial engineers. These materials can be mixed with normal materials, which expand on heating, with the final aim of producing a composite material with its thermal expansion adjusted to a particular value, typically zero, and maintained even at the extremely low operating temperatures used in cryogenic and aerospace engineering.
In a new study published in Nature Communications, Nagoya University-led researchers report a reduced ruthenate ceramic material, made up of calcium, ruthenium and oxygen atoms, that shrinks by a record-breaking 6.7% when heated.
This is more than double the current record for a negative thermal expansion material, and the bulk material expands again when it is cooled. The results may provide industrial engineers with a new class of composite materials that can be used to increase the accuracy of processes and measurements, to improve the stability of device performance, and to prolong device lifetimes.
The size of the volume change, as well as the operating temperatures for negative thermal expansion can be controlled by changing the composition of the material. When the ruthenium atoms are partially replaced by iron atoms, the temperature window for negative thermal expansion gets much larger. This window extends to above 200 °C for the iron-containing material, which makes it particularly promising for industrial use.
Noting that the volume changes were triggered at the same temperature that the reduced ruthenate material changed from a metallic to a non-metallic state, the researchers looked at changes in the arrangement of the atoms using X-ray techniques. They saw dramatic changes on heating, with the internal atomic structure expanding in some directions but contracting in others.
Although the internal structure showed a net contraction, the crystallographic changes were not big enough to explain the giant volume changes in the bulk material. Instead, the researchers turned their attention to the material's overall structure, and found empty voids around the ceramic grains.
"The non-uniform changes in the atomic structure seem to deform the microstructure of the material, which means that the voids collapse and the material shrinks," study corresponding author Koshi Takenaka says. "This is a new way of achieving negative thermal expansion, and it will allow us to develop new materials to compensate for thermal expansion."
Their article, "Colossal negative thermal expansion in reduced layered ruthenate" was published in Nature Communications at DOI: 10.1038/ncomms14102
Koomi Sung | EurekAlert!
The stacked colour sensor
16.11.2017 | Empa - Eidgenössische Materialprüfungs- und Forschungsanstalt
Counterfeits and product piracy can be prevented by security features, such as printed 3-D microstructures
16.11.2017 | Karlsruher Institut für Technologie (KIT)
The formation of stars in distant galaxies is still largely unexplored. For the first time, astron-omers at the University of Geneva have now been able to closely observe a star system six billion light-years away. In doing so, they are confirming earlier simulations made by the University of Zurich. One special effect is made possible by the multiple reflections of images that run through the cosmos like a snake.
Today, astronomers have a pretty accurate idea of how stars were formed in the recent cosmic past. But do these laws also apply to older galaxies? For around a...
Just because someone is smart and well-motivated doesn't mean he or she can learn the visual skills needed to excel at tasks like matching fingerprints, interpreting medical X-rays, keeping track of aircraft on radar displays or forensic face matching.
That is the implication of a new study which shows for the first time that there is a broad range of differences in people's visual ability and that these...
Computer Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. In PNAS, a team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometers. The first test application: Together with colleagues from the University of Kassel and Helmholtz-Zentrum Geesthacht the researchers analyzed the locomotory system of a velvet worm.
During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles....
The quantum world is fragile; error correction codes are needed to protect the information stored in a quantum object from the deteriorating effects of noise. Quantum physicists in Innsbruck have developed a protocol to pass quantum information between differently encoded building blocks of a future quantum computer, such as processors and memories. Scientists may use this protocol in the future to build a data bus for quantum computers. The researchers have published their work in the journal Nature Communications.
Future quantum computers will be able to solve problems where conventional computers fail today. We are still far away from any large-scale implementation,...
Pillared graphene would transfer heat better if the theoretical material had a few asymmetric junctions that caused wrinkles, according to Rice University...
15.11.2017 | Event News
15.11.2017 | Event News
30.10.2017 | Event News
17.11.2017 | Physics and Astronomy
17.11.2017 | Health and Medicine
17.11.2017 | Studies and Analyses