Nav: Home

Birth of a hybrid

December 14, 2018

Materials scientists from NUST MISIS and the Merzhanov Institute of Structural Macrokinetics & Materials Science have developed a new method for producing bulk MAX-phases -- layered materials which simultaneously possess the properties of metals and ceramics. By combining the methods of self-propagating high-temperature synthesis and high-temperature shear deformation, it was possible to obtain sufficiently large samples of mixed titanium and aluminum carbide, which in the future can be used as high-temperature heating elements, according to the research paper published in Ceramics International.

Despite the fact that people have been making and working with ceramic materials for about 30 thousand years, scientists are still developing new methods for its production. MAX-phases are layered ceramic materials which contain three elements in their composition: M-metal (most often theses are elements of transition metals), A -- metal/nonmetal (as a rule, these are elements from the 13th and 14th groups, i.e. 3A or 4A -- in a short-period version from the periodic table), and X -- nitrogen or carbon. The resulting nitrides or carbides have the common formula Mn+1AXn (n being from one to three), and have a hexagonal layered structure, thereby acquiring a rather unusual combination of physical properties. These substances have properties of both metals and ceramics: in particular, they have high electrical and thermal conductivity, but resistance to sudden changes in temperature and significant mechanical loads. Materials from this family were first obtained in the 1960s, but scientists have only begun to actively study them over the last decade. Recently various methods have been developed to obtain these materials, the most popular of which being chemical or physical vapor deposition, spark plasma sintering, and hot isostatic pressing. At the same time, the materials are often synthesized in the form of small samples, so a separate technological task based on the MAX phase is necessary to obtain the material in bulk. For this purpose, various options for sintering powder materials are used but all the existing methods are either too technologically complex and therefore expensive, or require several long additional stages to increase the density of the initially porous materials, which does not allow scientists to achieve a sufficient share of the MAX phase in the final material.

The research team from NUST MISIS, led by Denis Kuznetsov, a Candidate of Technical Sciences, has proposed a new method of single stage MAX phase synthesis with a composition of Ti3AlC2 -- a promising material for use as a high-temperature heating element. To obtain it, scientists used a combination of already known methods of self-propagating high-temperature synthesis and shear deformation under pressure. The researchers have also compared two methods of pressing: extrusion pressing, during which the presses' powder was squeezed into a special form, creating rod-like elements, and uniaxial compression, in which the pressed powder was simply squeezed when heated, turning it into plates. The temperature was about 1700 degrees Celsius during pressing, and the whole process lasted about 20-25 seconds.

As a result of this proposed approach, the materials scientists were able to obtain two types of samples with fairly similar characteristics. Both in plates and rods, the density exceeded 95 percent, relative to the powdered material, and the Ti3AlC2 content ranged from 67 to 82 percent.

At the same time, this method's mechanical and physical parameters slightly beat out the samples obtained by extrusion: the compressive strength of those materials was 720 megapascals, while samples obtained through compression only registered a compressive strength of 641 megapascals. Additionally, the samples' registered a better Young`s modulus -- 221 gigapascals to 198, and thermal conductivity -- 22.9 watts per meter when heated by one degree to 22.1 than the compression samples.

According to the researchers, the main advantage of their proposed method is the ability to quickly obtain a relatively bulk material in just one stage -- it doesn't require high temperatures and long hours of sintering. In such a case, the share of MAX-phase in the final substance is quite high, so in the future these materials can be used in devices operating at high temperatures (around 1500 degrees Celsius), such as heating elements or coating for electrical contacts.

National University of Science and Technology MISIS

Related Thermal Conductivity Articles:

Understanding river thermal landscapes
The BioScience Talks podcast features discussions of topical issues related to the biological sciences.
Granular material conductivity increases in mysterious ways under pressure
In a recent study published in EPJ E, a French team of physicists made systematic measurements of the electrical resistance -- which is inversely related to conductivity -- of metallic, oxidized granular materials in a single 1-D layer and in 3-D, under compression.
Understanding a river's 'thermal landscape' may be the key to saving it
Inexpensive sensor technologies have enabled an explosion in the availability of river temperature data and in statistical models for understanding them.
Reducing down to one-third of thermal resistance by WOW technology for 3-D DRAM application
Researchers at Tokyo institute of Technology presented a design guide for reducing 30 percent of thermal resistance for three-dimensional stacked devices compared with the conventional ICs using solder bump joint structure.
Building a market for renewable thermal technologies
A Yale-led analysis concludes that renewable thermal technologies have significant market potential in the state if supported by appropriate public policy and financing tools.
More Thermal Conductivity News and Thermal Conductivity Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Teaching For Better Humans
More than test scores or good grades — what do kids need to prepare them for the future? This hour, guest host Manoush Zomorodi and TED speakers explore how to help children grow into better humans, in and out of the classroom. Guests include educators Olympia Della Flora and Liz Kleinrock, psychologist Thomas Curran, and writer Jacqueline Woodson.
Now Playing: Science for the People

#535 Superior
Apologies for the delay getting this week's episode out! A technical glitch slowed us down, but all is once again well. This week, we look at the often troubling intertwining of science and race: its long history, its ability to persist even during periods of disrepute, and the current forms it takes as it resurfaces, leveraging the internet and nationalism to buoy itself. We speak with Angela Saini, independent journalist and author of the new book "Superior: The Return of Race Science", about where race science went and how it's coming back.